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Q23. Why was it necessary to change the basis of classification from atomic mass to atomic number? Q24. Elements A, B and C constitute a Dobereiner’s triad. What is the relationship in their atomic masses? Q25. How many elements were included in the arrangement given by Newland? Q26. Which property of atoms was used by Mendeleev to classify the elements? Q27. How many groups were originally proposed by Mendeleev in his periodic table? Q28. Where in the periodic table are chemically similar elements placed, in a group or in a period? Q29 Mendeleev’s periodic table had some blank spaces in it. What do they signify? Q30. What name was given to the element whose properties were similar to the element eka-aluminium predicted by Mendeleev? SHORT ANSWER QUESTIONS :(2-3 marks each) Q1. The elements of the third period of the Periodic Table are given below: Group → I II III IV V VI Vii Period ↓ 3 Na Mg Al Si P S Cl (a) Which is more non – metallic, S or Cl? (b) Which has higher atomic mass, Al or Cl? (c) What is the formula of an oxide of Al? Q2. Give the symbol for i. a metal of group 2 ii. a metal of group 13 iii. two non- metals of group 16 iv. most reactive non- metal of group 17. Q3. Why does atomic size progressively become smaller (atomic radius decreases from Na to Cl? How does it influence the ionization enthalpy or energy? Q4. Calcium is an element with atomic number 20. i. Is it a metal or a non – metal? ii. Is it more reactive than Mg or less reactive? iii. What will be its valency? iv. What would be the formula of its chloride? [101]

v. Will it be larger than K or smaller? Q5. These questions refer to the elements of periodic table with atomic numbers 3 to 18. i. Which of them are noble gases? ii. Which of them are halogens? iii. Which of them are alkali metals? iv. Which are the elements with valency 4? Q6. An element with atomic number 3 combines with another element with atomic number 17. What would be the formula of the compound? Q7. What is the electronic configuration of the element with atomic number 10? Q8. What is meant by periodic? What are its causes? Q9. (i) Mention one property each of elements in a group and of element in a period in Modern Periodic Table. (ii) What is the number of valence electrons in magnesium and sulphur whose atomic numbers are 12 and 16 respectively? Q10. Elements A, B, C and D have atomic numbers 1, 8, 11 and 19 respectively. Choose the odd element and give reason for your answer. Q11. Out of Li and K, which will have stronger metallic character and why? Q12. X is an element of modern periodic table. It is surrounded by elements having atomic number 17, 34, 36 and 53. (i) What is the atomic number of X? (ii) Predict its position in the periodic table. (iii) Which among these do not belong to the same Group? Q13. The atomic radii of three elements A, B and C of the Periodic Table are 186 pm, 104 pm and 1433pm respectively. Giving a reason, arrange these elements in the increasing order of atomic numbers in the period. Q14. An atom has electronic configuration 2, 8, 7. i. What is the atomic of this element? ii. To which of the following elements would it be chemically similar? N (7), F (9) , P (15) , Ar (18) Q15. (a) Can the following groups of elements be classified as Dobereiner’s triad? (i) . Na, Si, Cl (ii) Be, Mg, Ca Explain by giving reason. (Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40) [102]

(b) Upto which element, the law of octaves was found to be applicable? Q16. How does the tendency to gain electrons changes from Group 1 to Group 17? Give reason for your answer. Q17. The atomic number of elements A, B, C, D and E are given below. Element AB C D E Atomic Number 7 10 12 4 19 From the above table, answer the following questions. (i) Which two elements are chemically similar? (ii) Which element is an inert gas? (iii) Which element belongs to 3rd period of periodic table? (iv) Which element among these is a non-metal? Q18. The atomic number of S and Cl is 16 and 17 respectively and they belong to the same period. i. which one would have smaller atomic size? ii. which one would be more electronegative? iii. to which group would each one belong? Q19. Two elements P and Q belong to the 3rd period of the modern periodic table and are in group 1 and group 2 respectively. Compare their following characteristics in tabular form: ● The number of electrons in their atoms ● The sizes of their atoms ● Their metallic character ● Their tendencies to lose electrons ● The formula of their oxides ● The formula of their chlorides. Q20. Locate the position in Periodic Table of the following elements on the basis of their properties: i. An element which is an inert gas with atomic number 10. ii. An element which is tetravalent and basic element of organic chemistry. iii. A soft metal stored under kerosene and cut with knife. Q21. Two elements X and Y have atomic number 12 and 16 respectively. i. Write the electronic configuration off both. ii. Which type of bond will they form? iii. Write the formula of the compound formed by their combination (in term of X and Y). [103]

Q22. Why do all the elements of the same group have similar properties, same period have different properties? Q23. How does the electronic configuration of n atom of an element relate to its position in the Modern Periodic Table? Explain with one example. Q24. (i) What is a metalloid? (ii) Give the names of the metalloids in the Periodic Table along with their atomic number. (iii) In which groups of the Periodic Table are they located? Q25. An element ‘X’ with electronic configuration (2,8,2) combines separately with two radicals, (NO3) − and (SO4) 2−. i. Is ‘X’ a metal or a non-metal? Write the nature of its oxide ii. Write the formula of the compounds of ‘X’ formed by the combination of these radicals. Are these compounds covalent or electrovalent? Q26. From the part of a periodic table, answer the following questions: 1 2 13 14 15 16 17 Hydrogen Carbon Oxygen Fluorine XP Q YR ZT (i) Atomic number of oxygen is 8. What would be the atomic number of fluorine? (ii) Out of X and Q which element has larger atomic size? Give reason for your answer. (iii) Out of Y and Z which element has smaller atomic size? Give reason for your answer. Q27. Name: (a) three elements that have a single electron in their outermost shells. (b) two elements that have two electrons in heir outermost shells. (c) three elements with filled outermost shells. Q28. In the Modern periodic table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium? Q29. Can the following groups of elements be classified as Dobereiner’s triad? (a) Na, Si, Cl [104]

(b) Be, Mg, Ca Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40. Q30. How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period. Q31. Three elements ‘X’, ‘Y’ and ‘Z’ having atomic numbers 11, 7 and 6 respectively react with oxygen to form their oxides. (a) Arrange these oxides in increasing order of their basic nature. (b) Give reason for your answer. Q32. An element of group 15 has atomic number 15. Write the number of shells in its configuration. Write its configuration and find its valency. Examine if this element will have metallic properties or not. Q33. Halogens are placed in a separate group in the Modern Periodic Table. (a) State their group number. (b) How many valence electrons does each have? (c) What is the type of ions formed by them? (d) Name any two halogens. Q34. Name three elements which have only one electron in their outermost shell. How will their atomic size and metallic property change down the group? Q35. Arrange giving reason for elements in increasing order of their atomic size: Mg, N, P (Given that Mg and P belong to 2nd and 15th group respectively of 3rd period and N belongs to 15th group of 2nd period) . Q36. Consider two elements ‘A’ (Atomic number 17) and ‘B’ (Atomic number 19): (a) Write the positions of these elements in the Modern Periodic Table giving justification. (b) Write the formula of the compound formed when ‘A’ combines with ‘B’. (c) Draw the electron- dot structure of the compound and state the nature of the bond formed between the two elements. Q37. The element Be, Mg, Ca are placed in the second group of the periodic table. Their atomic numbers are 4, 12, 20 respectively. (a) Write the electronic configuration of these elements. (b) Write the valency exhibited by them. (c) Which of the three elements will be most reactive? [105]

Q38. Two elements X and Y belong to group 1 and 2 respectively in the same period of the periodic table. Compare these elements with respect to: (a) number of electrons in their outermost orbit (b) their valencies (c) metallic character (d) their atomic size (e) formula of their chlorides (f) formula of their sulphates. LONG ANSWER (5 MARK QUESTIONS) Q1. Mendeleev’s predicted the existence of certain elements not known at that time and named two of them as Eka- silicon and Eka-aluminium. i. Name the elements which have taken the place of these elements. ii. Mention the group and the period of these elements in the modern periodic table. iii. Classify these elements as metals, non-metals or metalloids. iv. How many valence electrons are present in each one of them? Q2. What is meant by group in the modern periodic table? How do the following changes occur on moving from top to bottom in a group? i. Number of valence electrons ii. Number of occupied shells iii. Size of atoms iv. Metallic character of element v. Effective nuclear charge experienced by valence electrons Q3. Consider two elements A (atomic number = 17) and B (atomic number= 19) i. Write the positions of these elements in the modern periodic table giving justification. ii. Write the formula of the compound formed when A combines with B. iii. Draw the electron dot structure of the compound and state the nature of the bond formed between the two elements. Q4. An element is placed in 2nd group and 3rd period of the periodic Table, burns in presence of oxygen to form a basic oxide. i. Write the electronic configuration. ii. Write a balanced equation when it burns in the presence of air. iii. Write a balanced equation when this oxide is dissolved in water. iv. Draw the electron dot structure for the formation of this oxide. \\ v. Identify the element. Q5. i. Why do we classify elements? ii. What are the two criteria used in the development of Modern Periodic Table? iii. State the position of (a) metals, [106]

(b) non-metals and (c) metalloids in the periodic table. iv. Would you place two isotopes of chlorine; Cl-35 and Cl-37 in different slots of the periodic table because of their different atomic masses or in the same slot because their chemical properties are same? Justify your answer. Q6. i. Why did Mendeleev have gaps in his periodic table? ii. State any three limitations of Mendeleev’s classification? iii. How do electronic configurations of atoms change in a period with an increase in atomic number? Q7. i. What was the basis of Mendeleev’s classification of elements? ii. List two achievements of Mendeleev’s Periodic table. iii. List any two observations which posed a challenge to Mendeleev’s Periodic Law. Q8 i. The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts. ii. Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass. Q9. Explain giving justification the trends in the following properties of elements, on moving from left to right in a period, in the Modern Periodic Table: i. Variation of valency. ii. Change of atomic radius. iii. Metallic to non-metallic character. iv. Electronegative character. v. Nature of oxides. Q10. (a) An element which is an essential constituent of all organic compounds belongs to which group? Account for the following: ● Elements of group 18 are called zero-valent. ● If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride? ● An element X forms a chloride with formula XCI3. The element X would most likely be in the same group of the periodic table as for which of the following ● Na, Mg, AI or Ca. ● Elements of which groups will form acidic oxides? Q11. i. Consider the following elements: Na (11), AI (13), Cl (17), K (19) For the given elements, find out (a) valency (b) period number (c) group number ii. An element X belongs to group 17 and element Y belongs to group 1. What type of bond will they form? Q12. The positions of five elements in the periodic table are shown below: Group 1 Group 2 Group 15 Group 16 [107]

Period 1 A B Period 3 C DE What are the number of valence electrons in B? Identify the element(s) which i. will have the. smallest atomic radius? ii. will be the most metallic? iii. will form basic oxide? iv. will show valency three? v. will show greatest tendency to gain electron? Q13. (a) What is Modern Periodic Law? (b) Atomic masses of nickel and cobalt are respectively 58.7 and 58.9. Which of them should appear first in the Periodic Table? (c) In which groups of the Periodic Table are the elements germanium and strontium present? (d) What is meant by the Law of Octaves? (e) Which has the bigger size:- (i) out of chlorine and bromine? (ii) out of sodium and magnesium? Q14. The elements of a period of the Periodic Table are given below in order, from left to right with one of its element missing. Li Be B C O F Ne i. To which period do these elements belong? ii. One element of this period is missing. Which I the missing element and where should it be placed? iii. Which one of these elements in this period shows the property of catenation? iv. Which one of the above elements belong to the halogen series? v. Identify the noble gas. Q15. An element X which is a yellow solid at room temperature shows catenation and allotropy. X form two oxides which are also formed during the thermal decomposition of ferrous sulphur crystals and are the major air pollutants. i. Identify the element X. ii. Write the electronic configuration of X. iii. Write the balanced chemical of equation for the thermal decomposition of ferrous sulphate crystals. iv. What would be the nature (acidic/ basic) of oxides formed? v. Locate the position of the element in the Modern Periodic Table. Q16. An element X (atomic no. 11) reacts with an element Y (atomic no. 17) to form a monovalent halide. i. Identify the position of X and Y in group and period in the Periodic Table. [108]

ii. State whether these elements are metal or non- metal. iii. Describe nature of oxide of element X. iv. Draw electron dot structure of the halide. Q17. Two elements X an Y have atomic number 11 and 16 respectively. i. Write the electronic configuration of both. ii. Which type of bond will they form? iii. Write the formula of the compound formed by their combination (in terms of X and Y). Q18. Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral. Based on the above information answer the following questions: i. To which group or period of the Periodic Table do the listed elements belong? ii. What would be the nature of compound formed by a combination of elements B and F? iii. Which two of these elements could definitely be metals? iv. Which one of the eight elements is most likely to be found in gaseous state at room temperature? v. If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G. Q19. Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shells. It was found that elements A and G combine to form an ionic compound which can also be extracted from sea water. Oxides of the elements A and B are basic in nature while those of E and F are acidic. The oxide of element D is almost neutral. Answer the following questions based on the information given herein: i. To which group or period of the periodic table do the listed elements belong? ii. Which one of the eight elements is likely to be a noble gas? iii. Which one of the eight elements would have the largest atomic radius? iv. Which two elements amongst these are likely to be non-metals? v. Which one of these eight elements is likely to be a semi-metal or metalloid? READ THE PASSAGE AND ANSWER THE QUESTIONS FOLLOWING IT. Q1) Dimitri Mendeleev in Russia (1869) and Lothar Meyer in Germany (1870) independently recognized that there was a periodic relationship among the properties of the elements known at that time. Both published tables with the elements arranged according to increasing atomic mass. But Mendeleev went one step further than Meyer: He used his table to predict the existence of elements that would have the properties similar to aluminum and silicon, but were yet unknown. Although Mendeleev and Meyer had a long dispute over priority, Mendeleev’s contributions to the development of the periodic table are now more widely recognized [109]

Figure 1. (a) Dimitri Mendeleev is widely credited with creating (b) the first periodic table of the elements. i. Which property of atoms was used by Mendeleev to classify the elements? ii. How many groups were originally proposed by Mendeleev in his periodic table? iii. Where in the periodic table are chemically similar elements placed, in a group or in a period? iv. Mendeleev’s periodic table had some blank spaces in it. What do they signify? v. What name was given to the element whose properties were similar to the element eka- aluminium predicted by Mendeleev? Q2) Mendeleev’s original table positioned the elements according to atomic weight, but in 1913 Dutch amateur theoretical physicist Anton van den Broek suggested that the ordering principle for the periodic table lay instead in the nuclear charge of each atom. Physicist Henry Moseley, working at the University of Manchester, tested this hypothesis, also in 1913, shortly before his tragic death in World War I. Moseley put it, here was proof that “there is in the atom a fundamental quantity, which increases by regular steps as we pass from one element to the next.” This fundamental quantity, first referred to as atomic number in 1920 by Ernest Rutherford, who was then at the University of Cambridge, is now identified as the number of protons in the nucleus. i. According to the modern periodic law the properties of elements are periodic function of which property of theirs? ii. List any two defects of Mendeleev’s periodic table which have been corrected in the modern periodic table? iii. How many group and periods are present in the long form of periodic table? iv. What is the name of the family of elements present in group 2 of the modern periodic table? v. The elements that are present in the right hand portion of the periodic table are metals or non- metals? vi. How many elements are present in 6th period of the periodic table? Q3) The Periodic Table of Chemical Elements is one of the most significant achievements in science, capturing the essence not only of chemistry, but also of physics and biology.It is a unique tool, enabling scientist to predict the appearance and properties of matter on the Earth and in the rest of the Universe. [110]

Study the periodic table and answer the questions that follow. Q3. The atomic number of an element is 16. Predict i. the number of valence electrons in its atom ii. its valency iii. its group number iv. whether it is a metal or a non- metal v. the nature of oxide formed by it vi. the formula of its chloride Q4. (i) How are the following related? a. Number of valence electrons of different elements in the same group. b. Number of shells of elements in the same period. (ii) How do the following change? a. Number of shells of elements as we go down a group. b. Number of valence electrons of elements on moving from, left to right in a period. c. Atomic radius in moving from left to right along a period. d. Atomic size down a group. (iii) Which one of the following statements concerning elements in the Periodic Table is correct? a. Elements of the same group all have the same number of electrons in the outermost occupied electron shell. b. Elements of Group 16 occur as cations in ionic compounds. c. Oxides of elements in Groups 16 and 17 are basic. d. The halogens (Group 17) are all gases at room temperature. e. The Group 13 elements are all metals [111]

BIOLOGY CHAPTER: LIFE PROCESSES MULTIPLE CHOICE QUESTION 1. The amount of the filtrate formed by the kidneys per minute is called glomerular filtration rate (GFR) . GFR in a healthy individual is approximately 125 ml/minute, i.e., 180 litres per day. A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggest that (a) nearly 99 per cent of the filtrate has to be reabsorbed by the renal tubules (b) urine formation is not related to reabsorption (c) Filtrate does not contain water (d) Reabsorption occurs in Bowman’s capsule Read the following passage for the next two questions All the energy required for ‘life’ processes is obtained by oxidation of some macromolecules that we call ‘food’. Only green plants and cyanobacteria can prepare their own food; by the process of photosynthesis they trap light energy and convert it into chemical energy that is stored in the bonds of carbohydrates like glucose, sucrose and starch. We must remember that in green plants too, not all cells, tissues and organs photosynthesis. 2) Photosynthesis occurs in: (a) chloroplast (b) mitochondria (c) cytoplasm (d) protoplasm 3) We know we eat food for energy — but how is this energy taken from food? (a) The breaking of the C-C bonds of complex compounds through oxidation within the cells (b) By storage of simple molecules into complex form (c) Only carbohydrates are oxidised to release energy (d) Only animals need to respire to produce ATP, plants don’t respire. [112]

4) Study the systole and diastole duration of different chambers of heart during a cardiac cycle. Answer the question that follows 5) Which chamber/s of the heart takes rest for a longer duration? (a) Right atrium (b) Right ventricle (c) Both the atria (d) Both the ventricles 6) What is the duration of a heart beat? (a) 0.3 sec (b) 0.4 sec (c) 0.7 sec (d) 0.8 sec 7) Which of the following is absent in lymph? (a) Protein (b) RBC (c) WBC (d) Water 8) Most powerful digestive enzyme occurs in which cell organelles (a) Mitochondria (b) Chloroplast (c) Golgibody (d) Lysosome 9) Which one of the following substance is changed into amino acid after digestion (NTSE) (a) Protein (b) Carbohydrate (c) Fat (d) Nucleic acid 10) Which one of the following substance is changed into amino acid after digestion (NTSE) (a) Protein (b) Carbohydrate (c) Fat (d) Nucleic acid [113]

11) Source of Penicillin antibiotic is (NTSE) (a) Bacteria (b) Fungi (c) Virus (d) Algae 12) Lactic acid is produced when pyruvate is broken down. (NTSE) (a) in presence of oxygen in mitochondria (b) in absence of oxygen in mitochondria (c) in presence of oxygen in muscle cells (d) in absence of oxygen in muscle cells 13) Root pressure is effective way transporting water in xylem. (NTSE) This pressure is generated (a) in bright sunlight (b) during night (c) at very low temperature (d) in high trees 14) Separation of oxygenated and deoxygenated blood. (NSO) I. Fulfils energy requirement of the body II. Ensures the effective transfer of oxygen in the body (a) Both statements are true (b) Statement I is true but statement II is false (c) Statement I is false but statement II is true (d) Both the statements are false 15) Refer to the diagram of the human digestive system. What would be the likely consequence of swapping S and T i.e., from the stomach, food will pass through T to S? (NSO) (a) The digestive enzymes would be denatured. (b) The intestinal contents would be highly alkaline and would damage the wall of T. (c) The intestinal contents would be too dry and unable to pass through S properly. (d) Water absorption would be highly reduced. [114]

ASSERTION- REASON 15. In the following questions a statement of Assertion is followed by a statement of Reason. Mark the correct choice as (a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion. (c) If Assertion is true but Reason is false. (d) If Reason is true but Assertion is false. (e) If both Assertion and Reason are false. 1. Assertion -Arteries are thick walled blood vessels. Reason- Arteries have to carry blood towards the heart. 2. Assertion- Bile juice contains proteolytic enzymes. Reason- Proteolytic enzymes convert proteins into amino acids. 3. Assertion- In human beings, the respiratory pigment is haemoglobin. Reason- Haemoglobin is a protein that has a high affinity for carbon dioxide. 4. Assertion- Pyruvate is a 6 carbon molecule which is formed in the cytoplasm. Reason- Pyruvate is formed as a result of the first step of cellular respiration. 5. Assertion- The opening and closing of the stomatal pore is a function of guard cells. Reason- Exchange of gases is a function of stomata. 6. Assertion-The energy requirement of plants are less than of animals Reason- Plants make their own food by photosynthesis. 7. Assertion: Blood pressure is arterial blood pressure. Reason: It is measured by sphygmomanometer. 8. Assertion: Most fish when out of water, die of suffocation. Reason: Atmospheric air contains far less oxygen content than the dissolved oxygen in water. 9. Assertion: Lipases of bile help in the emulsification of fats. Reason: Lipases can break large fat droplets into smaller ones. 10. Assertion: Kidneys maintain the osmotic concentration of the blood. Reason: Kidneys eliminate either hypotonic or hypertonic urine according to the need of the body. [115]

VSA/SA/LA TYPE- 1. Does the bile juice contain any enzymes? What is its role in digestion? What will happen if bile juice is not produced? 2 (a) Name the three components of gastric juice released in the stomach 3 (b) Bile does not contain any enzymes but still helps in digestion. How? (c) How is the small intestine designed to absorb food? 17. a. All plants give out oxygen during the day and carbon dioxide at night. Do you agree with this statement? Justify your answer. 3 b. What will happen to the rate of photosynthesis in each of the following situations- 3 (i) Cloudy days (ii) Stomata get blocked by 18. Draw a neat, proportionate diagram of the human excretory system and label- (a) Blood vessel that brings nitrogenous waste to the kidney (b) The tubes that carry urine away from the kidneys. (c) The part where urine is stored The part from where urine is excreted 3 19. Mention the function of the following parts of the human excretory system- 3 5 a. Kidney b. Urinary bladder c. Urethra 20 (a) Name the filtration unit of the kidneys. (b) State the two steps of urine formation that occur here. 21. (a) Mention any two components of blood. (b) Trace the movement of oxygenated blood in the body. (c) Write the function of valves present in between atria and ventricles. (d) Write one structural difference between the composition of artery and veins. 22. (a) Define excretion. (b) Name the basic filtration unit present in the kidney. (c) Draw excretory system in human beings and label the following organs of excretory system which perform following functions: (i) form urine. [116]

(ii) is a long tube which collects urine from kidney. 5 (iii) store urine until it is passed out. 23. Draw the human respiratory system and label the trachea, bronchus, bronchioles and alveoli. What is common in the structural design of the lungs and the small intestine. 5 24. Trace the path taken by 4 cubes of cottage cheese(paneer) that you consumed as breakfast in the morning. Enlist the steps of digestion that occur during the process. 5 CASE STUDY/PARAGRAPH BASED 25) Chlorophyll is present in the green plastids chloroplast. Chlorophyll a and chlorophyll b are the green pigments. Other than chlorophyll, carotenoids (orange) and xanthophyll (yellow) pigments are also present in chloroplasts.The portion of spectrum from 400 nm to 700 nm is known as Phtosynthetically Active Region(PAR) . Chloroplasts is the site of photosynthesis. Study the graph given below and answer the questions that follows: (Fig A – Absorption of different wavelength by chlorophyll Fig B- Rate of photosynthesis in different wavelength of light) (i) Which pigment gives green colour to the leaves? Why do leaves appear green? (ii) In which wavelengths is the rate of photosynthesis highest? Why? (iii) In which wavelength is the rate of photosynthesis lowest? Why? (iv) Give the overall equation of photosynthesis? (v) Photosynthesis involves both oxidation and reduction reaction. Justify. [117]

26) This sequential event in the heart which is cyclically repeated is called the cardiac cycle and it consists of systole and diastole of both the atria and ventricles. As mentioned earlier, the heart beats 72 times per minute, i.e., that many cardiac cycles are performed per minute. From this it could be deduced that the duration of a cardiac cycle is 0.8 seconds. During a cardiac cycle, each ventricle pumps out approximately 70 mL of blood which is called the stroke volume. The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output. Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and averages 5000 mL or 5 litres in a healthy individual. The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output. For example, the cardiac output of an athlete will be much higher than that of an ordinary man. During each cardiac cycle two prominent sounds are produced which can be easily heard through a stethoscope. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves whereas the second heart sound (dub) is associated with the closure of the semilunar valves. These sounds are of clinical diagnostic significance. (i) What is the heart composed of? (ii) How are the two heart sounds produced? (iii) What enables our heart to maintain the rhythm of heart beat? (iv) What is cardiac output? (v) What is the function of the following: (a) Tricuspid and bicuspid valve (b) semilunar valves 27) The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme. The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins into proteoses and peptones (peptides). The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. HC1 provides the acidic pH (pH 1.8) optimal for pepsins. Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins. Small amounts of lipases are also secreted by gastric glands. Various types of movements are generated by the muscularis layer of the small intestine. These movements help in a thorough mixing up of the food with various secretions in the intestine and thereby facilitate digestion. The bile, pancreatic juice and the intestinal juice are the secretions released into the small intestine. (i) Name the term that describes the process typed in bold in the second paragraph. (ii) Name the proteolytic enzyme secreted only in infants? Why is it secreted only in infants? (iii) Mention two functions of HCl secreted in gastric juice. [118]

(iv) How do you think milk is digested in adults? 28) ROLE OF OTHER ORGANS IN EXCRETION Other than the kidneys, lungs, liver and skin also help in the elimination of excretory wastes. Our lungs remove large amounts of CO2, (approximately 200mL/ minute) and also significant quantities of water every day. Liver, the largest gland in our body, secretes bile-containing substances like bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs. Most of these substances ultimately pass out along with digestive wastes. The sweat and sebaceous glands in the skin can eliminate certain substances through their secretions. Sweat produced by the sweat glands is a watery fluid containing NaC1, small amounts of urea, lactic acid, etc. Though the primary function of sweat is to facilitate a cooling effect on the body surface, it also helps in the removal of some of the wastes mentioned above. Sebaceous glands eliminate certain substances like sterols, hydrocarbons and waxes through sebum. This secretion provides a protective oily covering for the skin. Do you know that small amounts of nitrogenous wastes could be eliminated through saliva too? (i) Name the glands present in our skin. Also mention the role of the glands. (ii) Which is the largest gland of our body? Why? (iii) Why is the liver known as ‘detoxifying organ” of our body? (iv) How are nitrogenous wastes produced in the body? CHAPTER: HOW DO ORGANISMS REPRODUCE? MULTIPLE CHOICE QUESTIONS 1. Which of the following is not a part of the female reproductive system in human beings? (A) Ovary (B) Uterus (C) Fallopian tube (D) Vas deferens (NTSE) 2. Number of sex chromosomes in human beings are (A) 23 (B) 46 (C) 1 (D) 2 (NTSE) 3. Budding type of Reproduction is found in- (A) Peepal (B) Bryophyllum (C) Rose (D) Sugar Cane (NTSE) 4. The Anther contains – (A) Sepals (B) Ovules (C) Pistil (D) Pollen-grains (NTSE) 5. Which part of the plant’s female reproductive system is responsible for stimulating the germination of pollen grains? (A) Ovary (B) Pollen tube [119]

(C) Generative nucleus (D) Stigma 6. Which of the following is NOT a characteristic feature of sexual reproduction? A) Sexual reproduction involves the fusion of two dissimilar reproductive cells. B) Sexual reproduction is observed in most organisms. C) Fertilization may take place inside or outside the body of the female. D) The offspring represents the characteristics of only one parent. 7. In which of the following labelled parts does ovulation, fertilization and implantation occur? A) Ovulation Fertilization Implantation WX Y B) Ovulation Fertilization Implantation ZW X C) Ovulation Fertilization Implantation YZ W D) Ovulation Fertilization Implantation XY Z 8. Which of the following options are true about sexual and asexual reproduction? Sexual reproduction Asexual reproduction [120]

(i) Involves two individuals (i) Involves only one individual parent (ii) Involves a simple process (ii) Involves a complex process (iii) Involves the union of two types of (iii) Involves a mature parent cell gametes A) Only (i) and (ii) B) Only (i) and (iii) C) Only (ii) and (iii) D) All the three 9. Identify W, X, Y and Z? X Y Z A) W Ovary Uterus Fallopian tube Vagina B) X Y Z W Uterus Vagina Ovary Fallopian tube Z C) X Y W Vagina Fallopian tube Ovary Uterus D) X YZ W [121]

Ovary Fallopian tube Uterus Vagina ASSERTION REASON 10. 1) In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) Assertion is false but the Reason is true. A. Assertion: The uterus prepares itself every month to receive a fertilised egg. Reason: The ovary releases one egg every month. B. Assertion: Ureter forms the common passage for both the sperms and urine. Reason: It never carries both of them at the same time. C. Assertion: Zygote is a diploid cell formed by fusion of sperm with Egg. Reason: Both the sperm and the egg are haploid. D. Assertion: Pollination is the transfer of pollen grain to the anther. Reason: Pollination is carried out by wind, birds and insects. E. Assertion: Contraception is used to avoid unnecessary pregnancies. Reason: Contraception is used by both males and females. VSA/SA/LA TYPE 11. Name the process by which an amoeba reproduces. Draw the various stages of its reproduction in a proper sequence. 2 12. Student is viewing under a microscope a permanent slide showing various stages of asexual reproduction by budding in yeast. Draw diagrams of what he observes in proper sequence. 2 13. (a) What is a carpel? Write the function of its various parts. (b) Define transpiration. List its two functions. 3 14.Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival – the one reproducing [122]

asexually or the one reproducing sexually? Give reason to justify your answer. 3 15.(a) What is translocation? Why is it essential for plants? 3 (b) Where do the substances in plants reach as a result of translocation? 16.Write the function of following parts in human female reproductive system: 5 (i) Ovary (ii) Oviduct (iii) Uterus 5 (b) Describe in brief the structure and function of placenta. 17.What is Pollination? How does it occur in plants? Explain how pollination leads to fertilisation. CASE STUDY/PARAGRAPH BASED 1. Answer the questions on the basis of your understanding of the following paragraph and related studied concepts. 1) The availability of food is an essential situation for food production. India is more or less self- sufficient in cereals but insufficient in pulses and oilseeds. Due to the changes in consumption patterns, demand for fruits, vegetables, dairy, meat, poultry and fisheries has been increasing. Hence, there is a need to raise crop diversification and improve allied activities. In this situation, plant tissue culture offers remarkable opportunities in in-vitro propagations, plant quality improvement and production of plants with desirable agronomical quality and quantity. It’s now possible to develop virus-free plant regeneration, herbicide resistance, salinity tolerance, disease resistance, incorporation of high protein content and genetically engineered plants for desirable traits. Micropropagated plant cells and tissues have been widely used for the production of secondary metabolites, which are the rich source of many pharmaceutical and industrial products. Crop plants play a major role in the human nutrition and health by providing carbohydrates, proteins, fats, minerals, antioxidants, vitamins, phytoconstituents and dietary fibres. (a) Why is tissue culture carried out? (2 points) (b) Mention one advantage of tissue culture over other methods of vegetative propagation. (c) Write one difference between Budding and Fission. (d) How are virus free propagated by tissue culture? 2) The pollen grain germinates on the stigma to produce a pollen tube. The contents of the pollen grain move into the pollen tube. Pollen tube grows through the tissues of the stigma and style and reaches ovary (a) What are the contents present in a pollen grain? (b) Why does the pollen tube have to reach the ovary? (c) What is present inside the ovary? (d) What is present in the ovule? [123]

CHAPTER: HEREDITY MULTIPLE CHOICE QUESTION 1. If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant (rr YY), the seeds produced in F1 generation are A) round and yellow B) round and green C) wrinkled and green D) wrinkled and yellow 2.Which law of Mendel is also known as the law of purity of gametes? A) Law of dominance B) Law of independent assortment C) Law of segregation D) Law of gravitation 3. To avoid self-fertilization Mendel removed the: A) Ovules of the flowers B) Anthers of the flowers C) Petals of the flowers D) Sepals of the flower 4. A trait of an organism which is developed in response to the environment is: A) Acquired trait B) Inherited trait C) Recessive trait D) Dominant trait 5. Which of the following statements appropriately defines the term gene? A) The process by which early organisms of the earth diversified into various new forms. B) Transmission of characteristics from parents to their offspring. C) The study of pattern of transmission of characters from parents to their offspring. D) Stretches of DNA containing coded information for making proteins. 6. If a pea plant with wrinkled seeds and heterozygous tall plants were self-pollinated, what will be the phenotypes of plants of F2 generation. (A) 75% plants will be tall and have wrinkled seeds and other 25% will be dwarf with wrinkled seeds. (B) 50% plants will be tall and have wrinkled seeds and other 50% will be dwarf with wrinkled seeds. (C) 50% plants will be tall and have wrinkled seed and other 50% will be dwarf with round seeds. [124]

(D) 25% plants will be tall and have wrinkled seed and other 75% will be dwarf with wrinkled seeds. (NTSE) 7.Two similar pea plants are growing in two different islands separated by a vast ocean. The phenomenon of geographical isolation will (A) not be seen as the plants get self-pollinated (NTSE) (B) be seen as the plants are growing in isolated regions (C) not be seen as the plants get pollinated by ocean water currents (D) be seen as the plants do not get pollinated and reproduces asexually 8. A Yellow and Round seeded pea plant has genotype YyRr. The gametes produced shall be (A) Yy, Rr (NTSE) (B) YR, yR, Yr, yr (C) YR, yr (D) Y, y, R, r 9. In Pisum sativum (pea plant) , the pods may be inflated (I, dominant) or constricted (i, recessive) . What proportion of the following crosses would be expected to be inflated? (A) II x ii (B) Ii x ii (C) II x II (D) Ii x Ii READ THE FOLLOWING PARAGRAPH FOR THE NEXT TWO QUESTIONS: Gregor Johann Mendel is known as the “Father of Genetics”. He had conducted experiments on pea plant (Pisum sativum) . He always used pure form (homozygous) for the trait for conducting the crosses. F1 generation was produced by cross pollinating two pairs of contrasting traits where F2 generation was produced by self-pollination (selfing). Only one of the parental trait appeared in F1 genration. No intermediate trait were observed by him. He used the term “Factors” as heredity units. Mendel’s factor is now known as ‘gene’.He conducted experiments on considering single pair of traits (monohybrid cross) and 2 pairs of trait (dihybrid cross) . 10. Why did Mendel observe one of the parental trait in F1 generation? (a) Expression of the traits were dependent on temperature and other climatic factors. (b) One allele is dominant over the other. (c) Alternately any of the contrasting traits appeared in F1 generation. (d) Expression of trait is dependent on the female gamete. [125]

11. What is the chemical composition of Mendel’s factor? (a) Protein (b) DNA (c) RNA (d) Gametes ASSERTION REASON QUESTIONS- 12. In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) Assertion is false but the Reason is true. (e) Both assertion and reason are false 1. Assertion-Changes in non-reproductive tissue can be passed on to the DNA of the germ cell. Reason- Inherited traits include the traits developed during the lifetime of an individual that cannot be passed on to its progeny. 2. Assertion- The dominant gene is able to express itself even in the presence of the recessive gene. Reason- The dominant gene is represented by a capital letter. 3. Assertion: The principle of segregation given by Mendel is the principle of purity A of gametes Reason: Gametes are pure for a character. VSA/ SA /LA QUESTIONS- 13. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F1 progeny? 2 14. (a) What are dominant and recessive traits? (b) ‘‘Is it possible that a trait is inherited but may not be expressed in the next generation?’’ Give a suitable example to justify this statement. 3 15. A cross was made between pure breeding pea plants one with round and green seeds and the Other with wrinkled and yellow seeds (a) Write the phenotype of F1 progeny. Give reason for your answer. (b) Write the different types of F2 progeny obtained along with their ratio when F1 progeny was selfed. 3 [126]

16. How many pairs of chromosomes are present in human beings? Out of these how many are sex Chromosomes? How many types of sex chromosomes are found in human beings? 3 17. \"The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it\". Draw a flow chart showing determination of sex of a newborn to justify this statement. 3 18. Guinea pig having black colour when crossed with guinea pig having the same colour produced 100 offspring, out of which 75 were black and 25 were white. Now find out- (a) What is the possible genotype of the guinea pig? (b) Which trait is dominant and which is recessive? (c) What is this cross called as and what is the ratio of F2 progeny obtained from this cross? 5 19. In a cross between plants with purple flowers and plants with white flowers, the offspring of F1 generation had all white flowers. When F1 generation individuals were self-bred, the F1 generation gave rise to 100 individuals, 75 of which had white flowers. Make a cross and answer the following: (a) What are the genotypes of F2 individuals? (b) What is the ratio of white to purple flowered plants in F2 generation? 5 20. Given here is a schematic diagram showing Mendel’s experiment on pea plants with yellow round and green wrinkled seeds. Answer the following questions: (a) Complete the diagram by filling numbers 1-6. (b) Write the phenotypes of F1 progeny, (c) Name the phenotypes produced in F2 progeny upon self pollination of F1 progeny. CHAPTER: OUR ENVIRONMENT MULTIPLE CHOICE QUESTIONS 1. What will happen if deer are missing in the following food chain- Grass Deer Lion a. The population of tigers will increase b. The amount of grass will increase c. The tigers will die d. The tigers will start eating grass [127]

2. Consider the following ecosystems- i. Ponds ii. Forests iii. Aquarium iv. Crop fields Which of the above are artificial? a. i and iv b. ii and iii c. ii and iv d. iii and iv 3. Paper cups were introduced in the railways to serve tea, intead of plastic cups because- a. Paper cups are more aesthetic b. Paper cups are non- biodegradable c. Plastic cups are bio degradable d. Paper cups are bio degradable (NTSE) 4. In the term Homo sapiens, ‘sapiens’ indicates a. Genus name b.Species b. Class name d. Family name 5. Ecological pyramid was first introduced by (NTSE) a. Darwin b. Mendel c, Willam Eltan d. Charles Elton 6. Which is a renewable resource- a. Coal b. Water c. Petrol d. Natural gas 7. The figure given below shows some of the changes that one may notice following discharge of sewage into a river. BOD refers to Biological Oxygen Demand DO refers to dissolved oxygen Select the correct answer based on the given figure BOD DO Justification [128]

(a) Higher low Water is polluted with organic waste (b) low high (c) Higher low Water is polluted with organic waste (d) Low high Water is polluted with organic waste but decomposition has not started There is no relation between BOD, DO and clean water Read the paragraph given below and answer the question that follows: Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere. There should be a balance between production and degradation of ozone in the stratosphere. Of late, the balance has been disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs) . CFCs find wide use as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts. 9. Which one of the following reactions depicts the process of ozone formation in stratosphere? (a) O+O+O O3 (b) O2 +O O3 (c) O2 O+O O+O2 O3 (d) All of the above 10. Which of the following is true for the role of CFC in the degradation of ozone layer? (a) CFC reacts with O3 (b) Cl released from CFC act as a catalyst (c) Cl released from CFC reacts with O3 (d) CFC act as a catalyst 11. Which of the following is true for the role of CFC in the degradation of ozone layer? (a) CFC reacts with O3 [129]

(b) Cl released from CFC act as a catalyst (c) Released from CFC reacts with O3 (d) CFC act as a catalyst ASSERTION REASON QUESTIONS- 1) In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) Assertion is false but the Reason is true. A. Assertion: Polybags and plastic containers are non-bio degradable substances. Reason: They can be broken down by saprophytes like bacteria and fungi. B. Assertion: herbivores are called the first order consumers. Reason: tiger is a top carnivore. VSA/SA/LA QUESTIONS- 13. In a 3-step food chain, state the trophic level at which the concentration of harmful chemicals is maximum. Why is this so? 2 14. Write 2 harmful effects of using plastic bags in the environment. Suggest alternatives to the use of plastic bags. 2 15. List any two eco-friendly practices that can be followed to dispose of the waste produced in our homes. 2 16. Complete the table given below- OXYGEN OZONE FORMULA i. ii. BENEFIT TO BIOTIC iii. iv COMPONENT 2 17 a. Autotrophs are at the first level of food chain. Give reason. b. In a food chain of frogs, grass, insects and snakes, assign trophic level to frogs. To which category of consumers do they belong? c. If the first level in the above food chain has 10,000 kJ of energy, how much energy will be obtained by the last level? 3 [130]

18. a. From the following groups of organisms, create a food chain which is most advantageous for humans in terms of energy- Hawk, Rat, Cereal plant, Goat, Snake, Humans 3 b. State the possible disadvantage if the cereal plant is growing in soil rich in pesticides. c. Construct a food web using the organisms mentioned above. 19 a. How is ozone layer formed? State its importance on all life forms on earth? Why the amount of ozone in the atmosphere dropped sharply in the 1980s? What are the harmful effects of this? b. State the full form of UNEP. 5 20 a. Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why? b. What are decomposers? What will be the consequence if the decomposers are completely eradicated from an ecosystem? Justify your answer. c. State with reason the consequence of decrease in the number of carnivores in an ecosystem. 21. Study the figure given below and answer the question that follows (a) Name and define phenomena depicted in the figure? (b) What type of substance is DDT- biodegradable or non-biodegradable? (c) What is the use of DDT? (d) Give any two reasons for the increase in concentration of DDT in the subsequent level of food chain. 5 [131]

PHYSICS CHAPTER: LIGHT – REFLECTION AND REFRACTION PASSAGE BASED QUESTION: Q1. The refractive index is dimensionless. It is a number that indicates the number of times slower than a light wave would be in the material than it is in a vacuum. The refractive index, represented by the symbol µ, is the velocity of light in vacuum divided by the velocity of light in a medium. The formula of the refractive index is as follows: µ=c/v Where, • µ is the refractive index • c is the velocity of light in a vacuum ( 3 × 108 m/s) • v is the velocity of light in a substance The vacuum has a refractive index of 1. The refractive index of other materials can be calculated from the above equation. Higher the refractive index, the higher the optical density and slower is the speed of light. (i) The speed of light in air 3x10 8 m/s and in glass it is 2x10 8 m/s . The refractive index of glass is ______. (a) 1.5 (b) 0.66 (c) 6 (d) none of these (ii) The speed of light in water is 2.25x10 8 m/s . The refractive index of water is ______. (a) 0.75 (b) 1.33 (c) 6.75 (d) none of these (iii) You are given three media A, B and C of refractive index 1.33, 1.65 and 1.46. The medium in which the light will travel fastest is (a) A (b) B (c) C (d) equal in all three media (iv) “The refractive index of diamond is 2.42”. What is the meaning of this statement in relation to speed of light? Q2. Sign Conventions of Spherical Mirror · All the distances are measured from the pole of the mirror as the origin. · Distances measured in the direction of incident rays are taken as positive. [132]

· Distances measured opposite to the direction of incident rays are taken as negative. · Distances measured upward and perpendicular to the principal axis are taken as positive. · Distances measured downward and perpendicular to the principal axis are taken as negative. 1/f=1/v+1/u …where f, v and u are focal length, image distance, object distance. Linear Magnification: This is the ratio of the height of the image to the height of the object. m=h‘/h …where m = magnification, h = height of image, h’ = height of object. According to Sign Conventions: i. Object distance in case of a concave mirror is taken as ____________. ii. Image distance in case of a concave mirror is taken as ____________. iii. Focal length in case of a concave mirror is taken as ____________. iv. Object distance in case of a convex mirror is taken as ____________. v. Image distance in the case of convex mirrors is taken as ____________. vi. Focal length in case of convex mirrors is taken as ____________. vii. Sign of the real image is considered as ___________. viii. Sign of a virtual image is considered as ___________. ix. m= +1 means image is _________ principal axis. x. m= -1 means image is _________ principal axis. VERY SHORT ANSWER TYPE QUESTIONS (1 MARKERS) 1. Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror. 2. Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror. 3. Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror. [133]

4. Redraw the diagram given below in your answer book and show the direction of the light ray after refraction from the lens. 5. Why does a ray of light bend when it travels from one medium into another? 6. Redraw the diagram given below in your answer book and show the direction of the light ray after refraction from the lens. 7. If a light ray IM is incident on the surface AB as shown, identify the correct emergent ray. 8. The refractive indices of four media A, B, C and D are given in the following table: If light, travels from one medium to another, in which case the change in speed will be (i) minimum, (ii) maximum? 9. Redraw the given diagram and show the path of the refracted ray: 10. What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is +3? 11. Between which two points of a concave mirror should an object be placed to obtain a magnification of -3? 12. The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide? [134]

13. Between which two points related to a concave mirror should an object be placed to obtain on a screen an image twice the size of the object? 14. How should a ray of light be incident on a rectangular glass slab so that it comes out from the opposite side of the slab without being displaced? 15. A girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens. State the reason for this observation. OBJECTIVE TYPE QUESTIONS 1. An object is placed at a distance of 0.25 m in front of a plane mirror. The distance between the object and image will be (a) 0.25 m (b) 1.0 m (c) 0.5 m (d) 0.125 m 2. The angle of incidence for a ray of light having zero reflection angle is (a) 0 (b) 30° (c) 45° (d) 90° 3. For a real object, which of the following can produce a real image? (a) Plane mirror (b) Concave mirror (c) Concave lens (d) Convex mirror 4. Which of the following mirrors is used by a dentist to examine a small cavity? (a) Convex mirror (b) Plane mirror (c) Concave mirror (d) Combination of convex and concave mirror 5. An object at a distance of 30 cm from a the concave mirror gets its image at the same point. The focal length of the mirror is (a) – 30 cm (b) 30 cm (c) – 15 cm (d) +15 cm 6. An object at a distance of + 15 cm is slowly moved towards the pole of a convex mirror. The image will get (a) shortened and real (b) enlarged and real [135]

(c) enlarge and virtual (d) diminished and virtual 7. A concave mirror of radius 30 cm is placed in water. It’s focal length in air and water differ by (a) 15 (b) 20 (c) 30 (d) 0 8. A concave mirror of focal length 20 cm forms an image having twice the size of the object. For the virtual position of object, the position of object will be at (a) 25 cm (b) 40 cm (c) 10 cm (d) At infinity 9. The image formed by the concave mirror is real, inverted and of the same size as that of the object. The position of object should be (a) at the focus (b) at the centre of curvature (c) between focus and centre of curvature (d) beyond centre of curvature 10. The nature of the image formed by concave mirror when the object is placed between the focus (F) and centre of curvature (C) of the mirror observed by us is (a) real, inverted and diminished (b) virtual, erect and smaller in size (c) real, inverted and enlarged (d) virtual, upright and enlarged 11. The nature of image formed by a convex mirror when the object distance from the mirror is less than the distance between pole and focal point (F) of the mirror would be (a) real, inverted and diminished in size (b) real, inverted and enlarged in size (c) virtual, upright and diminished in size (d) virtual, upright and enlarged in size 12. If a man’s face is 25 cm in front of concave shaving mirror producing erect image 1.5 times the size of face, focal length of the mirror would be (a) 75 cm (b) 25 cm (c) 15 cm (d) 60 cm 13. As light travels from a rarer to a denser medium it will have (a) increased velocity (b) decreased velocity (c) decreased wavelength (d) both (b) and (c) 14. The angle of incidence i and refraction r are equal in a transparent slab when the value of i is [136]

(a) 0° (b) 45° (c) 90° (d) depend on the material of the slab 15. The refractive index of transparent medium is greater than one because (a) Speed of light in vacuum < speed of light in transparent medium (b) Speed of light in vacuum > speed of light in transparent medium (c) Speed flight in vacuum = speed of light in transparent medium (d) Frequency of light wave changes when it moves from rarer to denser medium 16. The refractive index of water is 1.33. The speed of light in water will be (a) 1.33 × 108 m/s (b) 3 × 108 m/s (c) 2.26 × 108 m/s (d) 2.66 × 108 m/s 17. You are given three media A, B and C of refractive index 1.33, 1.65 and 1.46. The medium in which the light will travel fastest is (a) A (b) B (c) C (d) equal in all three media 18. Light from the Sun falling on a convex lens will converge at a point called (a) centre of curvature (b) focus (c) radius of curvature (d) optical centre 19. Large number of thin stripes of black paint are made on the surface of a convex lens of focal length 20 cm to catch the image of a white horse. The image will be (a) a zebra of black stripes (b) a horse of black stripes (c) a horse of less brightness (d) a zebra of less brightness 20. A diverging lens will produce (a) always real image (b) always virtual image (c) both real and virtual image (d) none of these 21. When object moves closer to convex lens, the image formed by it shift (a) away from the lens (b) towards the lens (c) first towards and then away from the lens (d) first away and then towards the lens 22. When object moves closer to a concave lens the image by it shift (a) away from the lens on the same side of object [137]

(b) toward the lens (c) away from the lens on the other side of lens (d) first towards and then away from the lens 23. A magnified real image is formed by a convex lens when the object is at (a) F (b) between F and 2F (c) 2F (d) only (a) and (b) both 24. The distance between the optical center and point of convergence is called focal length in which of the following cases? 25. A10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is (a) – 30 cm (b) – 20 cm (c) – 40 cm (d) – 60 cm ASSERTION & REASON DIRECTION: In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as: a. Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A). b. Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A). c. Assertion (A) is true but reason (R) is false. d. Assertion (A) is false but reason (R) is true. 1. Assertion: A point object is placed at a distance of 26 cm from a convex mirror of focal length 26 cm. The image will not form at infinity. Reason: For above given system the equation : 1/u + 1/v = 1/ f gives v = infinity [138]

2. Assertion: If a spherical mirror is dipped in water, its focal length remains unchanged. Reason: A laser light is focused by a converging lens . There will be a significant chromatic aberration. 3. Assertion: Large concave mirrors used to concentrate sunlight to produce heat in solar cookers. Reason: Concave mirror converges the light rays falling on it to a point. 4. Assertion: If the rays are diverging after emerging from a lens the lens must be concave. Reason : the convex lens can give diverging rays. 5. Assertion: light travels faster in glass than in air. Reason: glass is denser than air. 6. Assertion: Concave mirrors are used as reflectors in torches, vehicle head-lights and in search lights. Reason: When an object is placed beyond the center of curvature of a concave mirror, the image formed is real and inverted. 7. Assertion: The light emerges from a parallel-sided glass slab in a direction perpendicular with that in which enters the glass slab. Reason: The perpendicular distance between the original path of incident ray and emergent ray coming out of the glass slab is called lateral displacement of the emergent ray of light. 8. Assertion: When a pencil is partly immersed in water and held obliquely to the surface, the pencil appears to bend at the water surface. Reason: The apparent bending of the pencil is due to the refraction of light when it passes from water to air. SHORT ANSWER TYPE QUESTIONS (2 MARKERS) 1. Explain with the help of a diagram, why a pencil partly immersed in water appears to be bent at the water surface. 2. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed: a. at 2F1 b. between F1 and the optical center O of lens 3. A ray of light, incident obliquely on a face of a rectangular glass slab placed in air, emerges from the opposite face parallel to the incident ray. State two factors on which the lateral displacement of the emergent ray depends. 4. What is the minimum number of rays required for locating the image formed by a concave mirror for an object. Draw a ray diagram to show the formation of a virtual image by a concave mirror. 5. State the two laws of reflection of light. 6. Define and show on a diagram, the following terms relating to a concave mirror: [139]

a. Aperture b. Radius of curvature 7. Define the focus of a concave mirror. If the radius of curvature of a convex mirror is 30 cm, what would be its focal length? 8. Distinguish between a real and a virtual image of an object. What type of image is formed (i) by a plane mirror, (ii) on a cinema screen? 9. To instruct a ray diagram, we use two light rays which are so chosen that it is easy to know their directions after refraction from the lens. List these two rays and state the path of these rays after refraction. Use these two rays to locate the image of an object placed between ‘F and ‘2F of a convex lens. 10. List four properties of the image formed by a concave mirror, when the object is placed between focus and pole of the mirror. SHORT ANSWER TYPE QUESTIONS (3 MARKERS) 1. A concave lens has a focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed. 2. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. 3. An object 2 cm in size is placed 30 cm in front of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? What will be the nature and the size of the image formed? Draw a ray diagram to show the formation of the image in this case. 4. An object 2 cm high is placed at a distance of 64 cm from a white screen. On placing a convex lens at a distance of 32 cm from the object it is found that a distinct image of the object is formed on the screen. What is the focal length of the convex lens and size of the image formed on the screen? Draw a ray diagram to show the formation of the image in this position of the object with respect to the lens. 5. A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it forms a real and inverted image 20 cm away from the lens? What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case. 6. At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side. What will be the magnification produced in this case? [140]

7. How far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens? What will be the height of the image if the object is 6 cm tall? 8. The image of an object placed at 60 cm in front of a lens is obtained on a screen at a distance of 120 cm from it. Find the focal length of the lens. What would be the height of the image if the object is 5 cm high? 9. Define ‘refractive index of a transparent medium.’ What is its unit? Which has a higher refractive index, glass or water? 10. An object is placed between infinity and the pole of a convex mirror. Draw a ray diagram and also state the position, the relative size and the nature of the image formed. 11. State the type of mirror preferred as (i) rear view mirror in vehicles, (i0 shaving mirror. Justify your answer giving two reasons in each case. 12. The image of a candle flame placed at a distance of 45 cm from a spherical lens is formed on a screen placed at a distance of 90 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2 cm, find the height of its image. 13. A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. The distance of the object from the lens is 16 cm. Find the position, size and nature of the image formed, using the lens formula. 14. A 6 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 15 cm. The distance of the object from the lens is 10 cm. Find the position, size and nature of the image formed, using the lens formula. LONG ANSWER TYPE QUESTIONS (5 MARKERS) 1. Draw the ray diagram in each case to show the position and nature of the image formed when the object is placed: (i) at the center of curvature of a concave mirror (ii) between the pole P and focus F of a concave mirror (iii) in front of a convex mirror (iv) at 2F of a convex lens (v) in front of a concave lens 2. (a) It is desired to obtain an erect image of an object, using a concave mirror of focal length 20 cm. (i) What should be the range of distance of the object from the mirror? (ii) Will the image be bigger or smaller than the object? (iii) Draw a ray diagram to show the image formation in this case. [141]

(b) One half a convex lens of focal length 20 cm is covered with a black paper. (i) Will the lens produce a complete image of the object? (ii) Show the formation of an image of an object placed at 2F1 of such covered lens with the help of a ray diagram. (iii) How will the intensity of the image formed by a half-covered lens compare with a non-covered lens? ‘ 3. (i) If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it? (ii) Name the point on the lens through which a ray of light passes undeviated. (iii) An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find (a) the position (b) the magnification and (c) the nature of the image formed. 4. (i) What is meant by ‘power of a lens’? (ii) State and define the S.I. unit of power of a lens. (iii) A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with each other. Calculate the lens power of this combination. 5. (i) Draw a ray diagram to show the formation of an image of an object placed between infinity and the optical center of a concave lens. (ii) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate a. the distance of the object from the lens. b. the magnification for the image formed. c. the nature of the image formed. 6. (i) Under what condition will a glass lens placed in a transparent liquid become invisible? (ii) Describe and illustrate with a diagram, how we should arrange two converging lenses so that a parallel beam of light entering one lens emerges as a parallel beam after passing through the second lens. (iii) An object is placed at a distance of 3 cm from a concave lens of focal length 12 cm. Find the (a) position and (b) nature of the image formed. 7. List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms three times magnified real image of an object placed 16 cm in front of it. 8. State the law of refraction of light that defines the refractive index of a medium with respect to the other. Express it mathematically. How is the refractive index of any medium ‘A’ with respect to a medium ‘B’ related to the speed of propagation of light in two media A and B? State the name of this constant when one medium is vacuum or air. The refractive indices of glass and water with respect to vacuum are 3/2 and 4/3 respectively. If the speed of light in glass is 2 x 108 m/s, find the speed of light in (i) vacuum, (ii) water. [142]

9. To construct a ray diagram, we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these rays to locate the image of an object placed between the centre of curvature and focus of a concave mirror. 10. List the sign conventions that are followed in case of refraction of light through spherical lenses. Draw a diagram and apply these conventions in determining the nature and focal length of a spherical lens which forms three times magnified real image of an object placed 16 cm from the lens. CHAPTER: HUMAN EYE AND COLOURFUL WORLD PASSAGE BASED QUESTION: Q1. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. This refraction is due to the velocity of light through air, decreasing (the refractive index increases) with increased density. Atmospheric refraction near the ground produces mirages. Such refraction can also raise or lower, or stretch or shorten, the images of distant objects without involving mirages. Turbulent air can make distant objects appear to twinkle or shimmer. The term also applies to the refraction of sound. Atmospheric refraction is considered in measuring the position of both celestial and terrestrial objects. (1) Choose the correct statement a) the refractive index of air increases with increase in density. b) the refractive index of air decreases with increase in density. c) velocity of light through air decreasing with decreased density. d) velocity of light through air increases with increase in density. (2) Twinkling of stars is due to. a) Reflection of light by clouds b) scattering of light by dust particles c) dispersion of light by water drops d) atmospheric refraction of starlight (3) Choose the incorrect statement related to Mirage: a) It is an optical illusion. b) It happens when light moves from less dense to denser medium. c) It happens when light moves from denser medium to less dense medium. d) the image seen can be inverted also. Q2. Atoms or molecules which are exposed to light absorb light energy and re-emit light in different directions with different intensity. This phenomenon is an example of scattering, a general physical [143]

process where quanta of some form, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. The scattering of light is one of the most important phenomena in daily lives. This phenomenon has been seen by everyone from their childhood like the blue colour of the sky, the colour of the rainbow, etc. The scattering of light is completely different from the reflection and refraction of light. According to Rayleigh theory, a theoretical description of light scattering involving particles much smaller than the wavelength of the light, makes the sky blue. When light meets a molecule smaller than its wavelength, the electric fields temporarily polarise the molecule, re-distributing the electrons in the molecule such that one end has a weak positive charge, and the other has a weak negative charge. (1) Choose the correct statement a) Greater the wavelength of light, greater will be the scattering. b) Shorter the wavelength of light, lesser will be the scattering. c) Greater the wavelength of light, lesser will be the scattering. d) None of these. (2) Sky appears blue as: a) Red colour reflects first. b) Red colour reflects at last. c) Blue colour reflects first. d) Blue colour reflects at last. (a) & (b) (b) & (c) (a) & (c) (b) & (d) (3) _________________ & ________________ are the examples of scattering of light. Q3. Nalin and his four friends were sitting on his roof on a pleasant day. All of them were enjoying Ludo. Suddenly rains started, all of them ran in the shade. After half an hour, when rain stopped Ayush saw seven colours in the sky. He jumped with joy and shouted “Look, there is an Indra Dhanush in the sky”. Then Nalin explained all about the rainbow. A rainbow is a multi-coloured arc called visible spectrum formed with the order of colours being R (Red), O (Orange), Y (Yellow) , G (Green) , B (Blue) , I (Indigo) and V (Violet) from top to bottom. There are three properties of light in play when we observe a rainbow. -Refraction, Dispersion and total internal reflection of light. Rainbows are not limited to the dispersion of light by raindrops. The splashing of water at the base of a waterfall caused a mist of water in the air that often results in the formation of rainbows. A backyard water sprinkler is another common source of a Rainbow. After that everyone clapped for him. a) What information is given by Nalin to his friends about the conditions for the formation of a rainbow? [144]

b) Is it possible to obtain rainbow phenomenon on the earth? c) Which term is used for the seven colours of the rainbow? d) Which colour appears at the top and at the bottom of the rainbow? VERY SHORT ANSWER TYPE QUESTIONS (1 MARKERS) Q1. Define dispersion of white light. Q2. What is the twinkling of stars due to? Q3. What is the Tyndall effect? Q4. Give an example of a phenomenon where Tyndall effect can be observed. Q5. What is the colour of scattered sunlight when the size of the scattering particles is relatively large? Q6. What will be the colour of the sky when it is observed from a place in the absence of any atmosphere? Q7. The sky appears dark instead of blue to an astronaut. State its reason. Q8. Which phenomenon is responsible for making the path of light visible? Q9. Name the component of white light that deviates the least and the most while passing through a prism. Q10. The air layer of the atmosphere whose temperature is less than the hot layer behaves as optically _______________. MULTIPLE CHOICE/OBJECTIVE QUESTIONS Q1. When white light enters a glass prism from air, the angle of deviation is maximum for (a) blue light (b) yellow light (c) red light (d) violet light Q2. Which of the following is a natural phenomenon which is caused by the dispersion of sunlight in the sky? (a) Twinkling of stars (b) Stars seem higher than they actually are (c) Advanced sunrise and delayed sunset (d) Rainbow Q3. When light falls at critical angle on the surface of a rarer medium while coming from a denser medium, the refracting angle is ____________ . Q4. The dispersion of white light occurs because colours of white light at different ____________ through the glass prism. Q5.Match Column I with Column II. . Column I Column II [145]

(i) Twinkling stars (A) Suspended water drops (ii) Blue sky (B) Group of colours (iii) Rainbow (C) Scattering (iv) Spectrum (D) Changing atmosphere Q6. Refraction of light by the earth’s atmosphere due to variation in air density is called (a) atmospheric reflection (b) atmospheric dispersion (c) atmospheric scattering (d) atmospheric refraction Q7. The deflection of light by minute particles and molecules of the atmosphere in all direction is called ____________ of light. (a) dispersion (b) scattering (c) interference (d) tyndell effect Q8. One cannot see through the fog, because (a) refractive index of the fog is very high (b) light suffers total reflection at droplets (c) fog absorbs light (d) light is scattered by the droplets Q9. A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky? Q10. At noon the sun appears white as (a) light is least scattered [146]

(b) all the colours of the white light are scattered away (c) blue colour is scattered the most (d) red colour is scattered the most Q11 The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light (a) is scattered the most by smoke or fog (b) is scattered the least by smoke or fog (b) is absorbed the most by smoke or fog (c) moves fastest in air Q12. The bluish colour of water in deep sea is due to (a) the presence of algae and other plants found in water (b) reflection of sky in water (c) scattering of light (d) absorption of light by the sea ASSERTION AND REASON In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion. (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion. (c) Assertion is true but the Reason is false. (d) The statement of the Assertion is false but the Reason is true. 1. Assertion: Sun appears over the horizon two minutes before the actual sunrise. Reason: Light has to travel a larger distance in the atmosphere during sunrise. 2. Assertion: Danger and warning signs are red in color. Reason: Red light has a larger wavelength. 3. Assertion: Stars appear to twinkle at night. Reason: Layers of atmosphere have different density and move at different speed. This constantly changes the refractive index of the atmosphere and the apparent position of star. 4. Assertion: Sky appears to be blue during daytime. Reason: Red light has the largest wavelength. SHORT ANSWER TYPE QUESTIONS (2 MARKERS) Q1. Name the type of particles which act as prisms in the formation of rainbow in the sky. Q2. Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the Sun gets above the horizon. [147]

Q3. Describe an experiment to discuss the recombination of dispersed light. Q4. Explain why do stars twinkle and planets do not? Q5. Why does the clear sky appear blue? How would the sky appear in the absence of earth’s atmosphere? Q6. Which colour of white light suffers (i) least deviation and (ii) maximum deviation when a beam of white light passes through a glass prism? SHORT ANSWER TYPE QUESTIONS (3 MARKERS) Q1. (a) What is meant by the dispersion of white light? Draw a diagram to show dispersion of white light by the glass prism. (b) Explain why the planets do not twinkle but the stars twinkle. Q2. What is a spectrum? Why do different coloured rays deviate differently on passing through a glass prism? Q3. (a) Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism. (b) A star appears slightly higher (above) than its actual position in the sky. Illustrate it with the help of a labelled diagram. Q4. What is the colour of the clear sky during day-time? Give reason for it. Q5. State the difference in colours of the Sun observed during sunrise , sunset and noon. Give explanation for each. Q6. When and where do we see a rainbow? How is a rainbow formed? Draw a labelled diagram to illustrate the formation of a rainbow. Q7. Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the colour of the sky be for an astronaut staying in the international space station orbiting the earth? Justify your answer giving reason. Q8. Explain with help of a labelled diagram, the cause of twinkling of stars. Q9 .A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram. (i) Write the name and cause of the phenomenon observed. (ii) Where else in nature is this phenomenon observed? (iii) Based on this observation, state the conclusion which can be drawn about the constituents of white light. [148]

Q 10. State the cause of dispersion of white light passing through a glass prism. How did Newton show that white light of Sun contains seven colours using two identical glass prisms. Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the focus of the first prism. LONG ANSWER TYPE QUESTIONS (5 MARKERS) Q1. (i) Draw a diagram to show the dispersion of white light by a glass prism. (ii) What is the cause of this dispersion? (iii) What happen to the light when the light coming out of one prim is made to fall on another identical prism as shown in the fig. Q2. What is atmospheric refraction? Use this phenomenon to explain the following natural events. (a) Twinkling of stars (b) Advanced sun-rise and delayed sunset Draw diagrams to illustrate your answers. Q 3. (a) Draw a ray diagram to explain the term angle of deviation. (b) Why do the component colours of incident white light split into a spectrum while passing through a glass prism, explain. (c) Draw a labelled ray diagram to show the formation of a rainbow. Q4. (a) What is dispersion of white light? What is the cause of such dispersion? Draw a diagram, to show the dispersion of white light by a glass prism. (b) A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why it is so. Q5. (a) Demonstrate an activity with a well labelled diagram to prove that white light is made up of seven colours. (b) Which colour of light bends least and which one the most while passing out from the prism. Also state the reason for the same. Q6. (a) How does refraction take place in the atmosphere? Why do stars twinkle but not the planets? (b) State any two effects of atmospheric refraction on the sun as observed from the earth. Q7.(a) Explain why colour of clear sky appears blue during the day with the help of diagram. (b) Explain why Sun looks reddish at the time of sunrise and sunset. [149]

CHAPTER: ELECTRICITY PASSAGE BASED QUESTION: 1. Resistivity is a measure of the resistance of a given size of a specific material to electrical conduction. It may also be referred to as the specific electrical resistance, or volume resistivity, although these terms are less widely used. Although materials resist the flow of electrical current, some are better at conducting it than others. The resistivity is a figure that enables comparisons of the way in which different materials allow or resist current flow. To enable resistivity figures to be meaningful, specific units are used for resistivity, and there are formulas for calculating it and relating it to the resistance in Ohms for a given size of material. The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m) . It is commonly represented by the Greek letter ρ, rho. It is given by the formula- ρ=RA/l Materials that conduct electrical current easily are called conductors and have a low resistivity. Those that do not conduct electricity easily are called insulators and these materials have a high resistivity. The resistivity of different materials plays a major role in selecting the materials used for electrical wire, within many electronic components including resistors, integrated circuits and many more. Electrical resistivities of some substances, in ohm-meter, at 20°C are given as follows: Silver Copper Tungsten Mercury Iron Nichrome 1.60 x 10 -8 1.62 x 10 -8 5.2 x 10 -8 94 x 10 -8 10 x 10 -8 10 x 10 -6 a. Out of the silver and copper, which is a better conductor of electric current and why? b. Which substance is preferred to be used for electrical transmission lines? Give reason. c. Name the material that you would advise to be used in the heater elements of electric heating device and why? d. Out of Cu and Fe, which one will you prefer to use in electric wire in domestic use? 2. Heating Effect of Electric Current When electric current is supplied to a purely resistive conductor, the energy of electric current is dissipated entirely in the form of heat and as a result, the resistor gets heated. The heating of resistors because of dissipation of electrical energy is commonly known as the Heating Effect of Electric Current. Some examples are as follows: When electric energy is supplied to an electric bulb, the filament gets heated because of which it gives light. The heating of electric bulbs happens because of the heating effect of electric current. [150]