202110241-TRIUMPH-STUDENT-WORKBOOK-PHYSICAL_SCIENCE-G08-PART1

AS6-Appreciation and aesthetic sense, Values Short Answer Type Questions 15. Answer the following questions in 3-4 sentences. (i) [(Session 5.3)] Why do you appreciate Gomatham Srinivas? Why is he famous? (ii) [(Session 5.3)] Write two points in appreciation of Nerella Venumadhav. CHAPTER 5. SOUND 149

AS7-Application to daily life, concern to bio diversity Short Answer Type Questions 16. Answer the following questions in 3-4 sentences. (i) [(Session 5.2)] Who is Bismillah Khan? Why is he famous? (ii) [(Session 5.2)] Have you heard of M.S. Subbulakshmi? Why is he famous? CHAPTER 5. SOUND 150

Objective Questions AS1-Conceptual Understanding 17. Choose the correct answer. (i) Which organ gives human beings the ability to produce sound? (A) Tongue (B) Esophagus (C) Trachea (D) Larynx (ii) This makes up the inner part of the ear: (A) Tympanum (B) Cochlea (C)Ear canal (D) Eardrum (iii) The shape of incus bone is_________ shaped. (A) hammer (B) anvil (C) rod (D) circular (iv) Sound can travel through . (A) solids only (B) liquids only (C)gases only (D)solids, liquids and gases (v) In dholak, sound is produced due to . (A) vibration of air (B) stretched strings (C)air column (D)stretched membrane (vi) To – and – fro or back and forth motion of an object from its mean position is termed as . (A) vibration (B) frequency (C)time period (D) amplitude (vii) The pitch of sound depends on the of the vibrating body. CHAPTER 5. SOUND 151

(A) medium of propagation (B) noise (C) frequency (D) amplitude (viii) Which of the following is/are one of the part of the speech organ that is/are involved in producing sounds? (A) Nose & throat (B) Eyes (C) Pharynx (D) Intestine (ix) Loudness of a sound is determined by the of vibration. (A) frequency (B) wavelength (C) speed (D) amplitude AS2-Asking questions and making hypothesis 18. Choose the correct answer. (i) Which order is correct for Pitch of sound? (A) Lion<adult man<insect<child<infant<adult woman (B) Lion<adult man<adult woman<child<infant<insect (C)Insect<adult man<adult woman<child<infant< lion (D)Lion<adult woman<adult man<child<infant<insect AS3-Experimentation and field investigation 19. Choose the correct answer. (i) Sound greater than is physically painful. (A) 20 dB (B) 40 dB (C)60 dB (D)80 dB AS4-Information skills and projects CHAPTER 5. SOUND 152

20. Choose the correct answer. (i) Length of vocal cords of a woman is man. (A) less than (B) greater than (C)slightly greater than (D)same as (ii) Vocal cords in men are about long. (A) 20 mm (B) 20 cm (C)2 mm (D)2 m AS5-Communication through drawing and model making 21. Choose the correct answer. (i) Identify the marked part in the following, which makes up the inner ear. (A) Tympanum (B) Cochlea (C)Ear canal (D)Ear drum AS7-Application to daily life, concern to bio diversity 22. Choose the correct answer. (i) The intensity of sound for normal conversation is_________. (A) 15 dB (B) 90 dB (C)60 dB (D)0 dB CHAPTER 5. SOUND 153

6. REFLECTION OF LIGHT AT PLANE SURFACES SESSION 1 LAWS OF REFLECTION AND FORMATION OF IMAGE BY A PINHOLE CAMERA 1.1 Mind Map SESSION 1. LAWS OF REFLECTION AND FORMATION OF IMAGE BY A ... 154

1.2 Terminology i. Reflection – Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. ii. Reflection of light – When light rays traveling in a medium reaches the boundary of other medium, they turn back to the first medium. This phenomenon of turning back of light into the same medium after striking the boundary of other medium is called Reflection of Light. iii. Incident ray – An incident ray is a ray of light that strikes a surface. iv. Reflected ray – The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. v. Pinhole camera – A pinhole camera is a simple camera without a lens and with a single small aperture, a pinhole. vi. Inverted image – Image that shows the subject upside down when projected or seen. vii. Blurred image – Image which is indistinct and hazy in appearance. SESSION 1. LAWS OF REFLECTION AND FORMATION OF IMAGE BY A ... 155

1.3 Key Concepts i. A source of light, an opaque object and a screen are needed to form a shadow. ii. Light travels in a straight line. iii. When light gets reflected from a surface, the angle of reflection is equal to the angle of incidence. iv. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. v. Principle of pinhole camera : Light rays from an object pass through a small hole to form an inverted image. vi. If we increase the size of the hole of the pinhole camera then we get a blurred image on the screen. vii. Light selects the path that takes least time to travel. This principle was first given by Pierre de Fermat, a French lawyer and an amateur mathematician. viii. When light gets reflected from a surface, it selects the path that takes the least time. That is why angle of incidence is equal to the angle of reflection. 1.4 Reflection on Concepts Q1. [AS1] State the laws of reflection. [Refer to TB page 90 Q2] A. Laws of reflection of light: (i) The angle of incidence is equal to the angle of reflection. (ii) The incident ray, reflected ray and normal to the plane of reflection at point of reflec- tion lie in the same plane. Q2. [AS1] Explain the process of formation of an image with a pinhole camera. Draw a ray diagram to show this.(Pg–90;TB Q.3) A. Formation of an image with a pinhole camera – With a pinhole camera, light is passed through a very small hole (pinhole), such as one made by a needle. When an object is exposed to sunlight or similar light, the light is reflected (scattered) in various directions.If we observe the object through the pinhole, the light which comes from the top of the object goes straight towards the bottom of the screen. Similarly the rays from the bottom of the object goes straight towards the top of the screen. This leads to the formation of an inverted image. SESSION 1. LAWS OF REFLECTION AND FORMATION OF IMAGE BY A ... 156

If we increase the size of the pin hole camera, we get a blurred image with big size. If the hole is very large, there will be a lot of light entering the pinhole camera, but no image will be seen at all. The size of the image: • Increases on increasing the distance between the screen and pinhole. • Decreases on increasing the distance between the object and pinhole. • Increases on increasing the size of the object. Objective Questions (1) Angle of incidence = Angle of reflection. This rule is explained by Prin- ciple. ( Pg 92;TB Q 1) (A) Fermat (B) Newton (C) Archimedes (D) Pascal Correct Answer: A SESSION 1. LAWS OF REFLECTION AND FORMATION OF IMAGE BY A ... 157

SESSION 2 INTRODUCTION TO PLANE MIRROR AND REFLECTION OF LIGHT BY PLANE MIRRORS 2.1 Mind Map Formation of image by plane mirror 2.2 Terminology i. Plane mirror – A plane mirror is a mirror with a flat (planar) reflective surface. ii. Reflector – One that reflects. e.g– a polished surface for reflecting light or other radia- tion. iii. Clamp – A device made of wood or metal that is used to hold two things together tightly. iv. Point object – A point object is refers to a tiny object which is calculated or counted as dot object to simplify the calculations. v. Object distance – The distance between the pole of the mirror and object is known as object distance. vi. Image distance – The distance between the pole of the mirror and image is known as image distance. vii. Plane of reflection – The plane in which the incident ray, reflected ray and normal lie is called the plane of reflection. SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 158

2.3 Key Concepts i. Silver metal is one of the best reflectors of light. ii. The thin layer of Silver or Aluminium is the reflecting surface at the backside of the mirror. iii. The plane in which the incident ray, reflected ray and normal lie is the plane of reflection. 2.4 Reflection on Concepts Q1. [AS1] Draw a ray diagram to understand the formation of an image for a pointed object by a plane mirror? Explain it. [Refer to TB page 90 Q5] A. In the following figure, O is a point object. Some rays from O reach the mirror and get reflected. When we look into the mirror, the reflected rays seem to be coming from the point I. So point I is the image of point object O. When we place an object in front of a mirror, we see an image of the same object in the mirror. The object is the source of the incident rays, and the image is formed by the reflected rays. In case of plane mirror the image formed is equal to the size of of the object. Q2. [AS1] If a ray incidents normally on a plane mirror, what will be the angle of reflection? [Refer to TB page 90 Q1] A. For a plane mirror: If the incident ray falls along the normal, the angle of incidence is 0 degree, hence the angle of reflection is also 0 degree. 2.5 Application of Concepts Q1. [AS2] Why can’t we see our image in a white sheet of paper though it reflects light? [Refer to TB page 91 Q4] SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 159

A. Actually, paper is not flat. There are tiny rough spots that we cannot feel. The surface of the paper is not smooth so it can’t reflect a cohesive image. Surface roughness also contributes diffuse reflection causing the rays of light from different parts of a potential image to bounce back at different angles. Multiple and diffuse reflections scatter the reflecting rays, and all information about the image is lost. It scatters any reflected light so you can’t see an image. Q2. [AS4] In the adjacent figure, AO and OB are incident ray and reflected ray respectively. <AOB = 90°. Find the values of angle of incidence and angle of reflection? [Refer to TB page 91 Q1] A. Angle of incidence = Angle of reflection = 45° Q3. [AS4] Bharath stands in front of a plane mirror at a distance of 5m from the mirror and observes his image in the mirror. If he moves 2m. towards the plane mirror, then what will be the distance between Bharath and the image? [Refer to TB page 91 Q2] A. We know the distance between the object and mirror is equal to the distance between the mirror and the image fomed. When Bharath stands at a distance of 5m from the mirror, the distance between the image formed and mirror is also 5m. But when Bharath moves 2m forward, then the distance between Bharath and mirror becomes 3m. So the distance between mirror and image is 3m. So, diatance between Bharath and image formed is 3+3= 6m. 2.6 Higher Order Thinking Skills Q1. [AS1] Two divergent rays originating from the same point have an angle of 10° between them. If they strike a plane mirror with the same incident angle, What will be the angle of reflection? [Refer to TB page 91 Q4] SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 160

A. 10° Q2. [AS4] Two plane mirrors are fixed at right angles to each other and an object is placed between them as shown in the figure. Trace the path of the rays by which an observer sees the final image in one of the mirrors? [Refer to TB page 91 Q3] A. In the case of mirrors at a right angle, two primary images and only one secondary image is formed. Two primary images are seen as a result of single reflection of the rays. One secondary image is seen as a result of double reflection of rays. To make the concept easy an easy ray diagram with the same conditions (right angle) is provided below. Students can refer the above diagram to trace the path of the rays by which an observer see the final image in one of the mirrors in the above question. Q3. [AS6] Observe the adjacent figure.AB and BC are two plane mirrors arranged at 120°. A ray incidents at an angle 55° on AB. Find the values of “x”? [Refer to TB page 92 Q1] SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 161

A. We know that the first reflected ray makes an angle of 55° with the normal.Thus this ray makes an angle of 90° –55° = 35° with the horizontal. From the triangle made by the first reflected ray and the two mirrors, we see that the first reflected ray makes an angle of 25° with BC (because the sum of the interior angles of any triangle is 180°). Therefore, this ray makes an angle of 65° with the normal to BC. From the law of reflection, the second reflected ray makes an angle of 65° with the normal to BC. So the value of x = 65° Q3. The size of the image in the mirror seems to be decreased when you move the object towards your eye from the mirror. Draw a diagram showing the angles depicting the situation. [Refer to TB page 91 Q5] A. When we move the object from the mirror to our eye, the image in the mirror seems to move back in the mirror. Then the distance from the image to our eye increases. The angle made by the image at our eye is smaller than the angle made by the object. That is why the image looks smaller than the object. Here in the following image, O1 is the position of object initially and I1 is the image of the same. O2 is the position of the object when moved towards the eye and I2 is the image of that. SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 162

2.7 Suggested Experiments Q1. [AS3] Find the plane of reflection experimentally for the incident ray which passes through the heads of the pins pierced infront of the mirror as shown in figure 8. [Re- fer to TB page 92 Q2] A. Take a drawing board and fix a white paper on it with the help of clamps. Draw a straight line AB at the centre of the paper and also a normal(ON) to AB at the point ‘O’. Draw a straight line PQ making a certain angle(angle i) with ON as shown in the below figure. Fix two pins at the points at the points P and Q on the paper vertically. Observe the image P of the pin P and Q of the pin Q, in the mirror kept along the line AB. Fix two more pins R and S in such a way that they are in same line as that of P and Q . Join R,S and O as shown in figure given figure. Adjust the pins so that they were pierced to same height on the board. Put a paper on the heads of pins. The plane where the paper touches the mirror is called as plane of reflection for the incident ray which passes through the heads of the pins. Q2. [AS3] Verify laws of reflection experimentally. [Refer to TB page 92 Q1] A. Students’ Activity. ( Student can follow the given procedure) SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 163

Aim – To verify the laws of reflection. Material required –Mirror strip, drawing board, white paper, pins, clamps, scale and pencil. Procedure – Take a drawing board and fix a white paper on it with the help of a clamp. Draw a straight line AB at the centre of the paper and also a normal(ON) to AB at the point ‘O’. Draw a straight line PQ making a certain angle(angle i) with ON as shown in the below figure. Fix two pins at the points P and Q on the paper vertically. Observe the image P of the pin P and Q of the pin Q, in the mirror kept along the line AB. Fix two more pins R and S in such a way that they are in same line as that of P and Q . Join R, S and O as shown in given figure. Measure the angle between RS and ON( Angle of reflection). You will find that angle of incidence (i)= angle of reflection (r). Repeat the experiment for different angles of incidence and and measure the corrre- sponding angle of reflection. Record your observation in table. SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 164

S.No. i r Is i=r 1 30 degree 30 degree (Y/N) 2 40 degree 40 degree Y 3 45 degree 45 degree 4 50 degree 50 degree Y Y Y In all cases the angle of reflection is equal to the angle of incidence. Hence first law of reflection is verified. Here the line passing through P and Q is called incident ray and it touches the pa- per. The line joining R and S is called reflected ray and it touches the same paper. ON is the normal to the mirror at ‘O’ and it touches the same paper. Hence Incident ray, reflected ray and normal lies on the same paper. Hence second law of reflection is verified. 2.8 Suggested Projects Q1. [AS4] Make a solar heater / cooker with plane mirrors and write a report on the process of making. [Refer to TB page 92 Q1] A. Students’ activity. For reference –You might have observed the TV dish antenna. Make a wooden iron/ frame in the shape of a TV dish antenna. Cut an acrylic mirror sheet into 8 or 12 pieces in the shape of isosceles triangle with a height equal to the radius of your dish antenna.The bases of 8 or 12 triangles together make the circumference of the dish. Stick the triangle mirrors to the dish as shown in figure. Your solar heater / cooker is ready. SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 165

Face it towards the sun. Find its focal point and place a vessel at that point. It will get heated. You can even cook rice in that vessel. Q2. [AS4] Generally periscopes are made in the shape of “Z” make your own periscope in the shape of “C” . Discuss the problem faced while using the periscope you made in the shape of “C” .Draw the ray diagram to explain the formation of image in “C” shaped periscope. [Refer to TB page 92 Q2] A. Students’ activity. Student can refer the following sites. • https://en.wikipedia.org/wiki/Periscope • https://www.youtube.com/watch?v=8TzXN5gunFg • https://in.answers.yahoo.com/question/index?qid=20140302001936AAPsO31 Objective Questions (1) A ray of light incidents on a plane mirror at an angle of 90° to its surface. What will be the angle of reflection? (Pg 92; TB Q 3) (B) 90° (A) 0° (C) 45° (D) 180° Correct Answer: A (2) If we move an object away from the plane mirror the size of the object seems to be –(Pg 92; TB Q4) (A) Increased (B) Decreased (C)Of the same size (D)Image can not be seen Correct Answer: B SESSION 2. INTRODUCTION TO PLANE MIRROR AND REFLECTION OF ... 166

SESSION 3 CHARACTERISTICS OF AN IMAGE FORMED BY PLANE MIRROR AND ITS USES 3.1 Mind Map 3.2 Terminology i. Lateral inversion – Lateral inversion is the effect produced by a plane mirror in reversing images from left to right. ii. Virtual image – A virtual image is an image formed when the outgoing rays from a point on an object always diverge. The image appears to be located at the point of SESSION 3. CHARACTERISTICS OF AN IMAGE FORMED BY PLANE MIR... 167

apparent divergence. A virtual image cannot be projected onto a screen. iii. Real Image – A real image is an image which is located in the plane of convergence for the light rays that originate from a given object. If a screen is placed in the plane of a real image the image will generally become visible on the screen. Examples of real images include the image seen on a cinema screen. 3.3 Key Concepts i. Image of a real object in a plane mirror is virtual, erect and the same size of the object. ii. When we move away from the plane mirror, the image in a plane mirror appears to be small because of the small angle subtended at our eye. iii. Image in a plane mirror suffers lateral inversion. iv. A virtual image is an image formed when the outgoing rays from a point on an object always diverge. The image appears to be located at the point of apparent divergence. A virtual image cannot be projected onto a screen. v. A real image is an image which is located in the plane of convergence for the light rays that originate from a given object. If a screen is placed in the plane of a real image the image will generally become visible on the screen. Examples of real images include the image seen on a cinema screen. 3.4 Reflection on Concepts Q1. [AS1] Why does the image in plane mirror suffer lateral inversion? [Reflection on con- cepts [Refer to TB page 90 Q4] A. Viewing an object in a mirror is actually viewing at its 180° rotated states. This is the source of lateral inversion. The light rays which come from the right side of the object get reflected from the plane mirror and reach our eye. Our brain feels that the ray( reflected ray) is coming from the inside of the plane mirror. That is why right side of the object appears as left side of the object. 3.5 Application of Concepts Q1. [AS1] Discuss the merits and demerits of using mirrors in building elevation ? [Refer to TB page 91 Q5] A. Merits of using mirrors: (i) They can be cut into different sizes. SESSION 3. CHARACTERISTICS OF AN IMAGE FORMED BY PLANE MIR... 168

(ii) They do not rust. (iii) They do not let water to pass through them. Demerits of using mirrors: (i) They can break easily. (ii) Using mirrors is more expensive. Q2. [AS5] Explain diagrammatically the image of letter ‘B’ in a plane mirror. [Refer to TB page 91 Q3] A. 3.6 Higher Order Thinking Skills SESSION 3. CHARACTERISTICS OF AN IMAGE FORMED BY PLANE MIR... 169

Q1. [AS1] Niharika holds a clock in her hand, which shows the time 3 o’clock. If she observes the clock in a plane mirror, what will be the time that the clock shows in the plane mirror? [Refer to TB page 91 Q2] A. The hands of a clock in the 3 o’clock position appears to be in the 9 o’clock position in the image. Objective Questions (1) Which of the following letters does not suffer lateral inversion? (Pg 93;TB Q 2) (A) C (B) O (C) B (D) N Correct Answer: B (2) Which of the following is incorrect with respect to the image in a plane mirror? (Pg 93;TB Q 5) (A) Image is erect (B) Size of the image is same as the size of object (C)Laterally inverted (D)Image is real Correct Answer: D SESSION 3. CHARACTERISTICS OF AN IMAGE FORMED BY PLANE MIR... 170

—— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions 1. Fill in the blanks. [Refer to Session 6.2 ] (i) A image cannot be projected onto a screen. (ii) The plane in which the incident ray, reflected ray and normal lie is called the . 2. State true or false. [Refer to Session 6.1 ] (i) Pinhole camera with a big hole will produce crispy image on the screen. ] [ 3. Answer the following questions in one sentence. [Refer to Session 6.1 ] (i) If a ray incidents normally on a plane mirror, what will be the angle of reflection? 4. Fill in the blanks. [Refer to Session 6.1 ] (i) First person who said light always selects the path which takes the least time to travel between two points is . CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 171

(ii) The incident ray, the normal at the point of incidence and the reflected ray all lie in the . Short Answer Type Questions 5. Answer the following questions in 3-4 sentences. (i) [(Session 6.1)] State the laws of reflection. (ii) [(Session 6.1)] What would happen if we increase the size of the hole of the pinhole camera? CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 172

Long Answer Type Questions 6. Answer the following questions in 6-8 sentences. (i) [(Session 6.1)] Explain the process of formation of an image with a pinhole camera? Draw a ray diagram to show this. CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 173

AS2-Asking questions and making hypothesis Short Answer Type Questions 7. Answer the following questions in 3-4 sentences. (i) [(Session 6.2)] Ritu asks her father that why “AMBULANCE” is written reverse on the Ambulance Vehicle? What her father might have answered? CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 174

(ii) [(Session 6.2)] What would you do to obtain figures that are shown in figure 2 using mirror strip and figure 1. CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 175

AS3-Experimentation and field investigation Long Answer Type Questions 8. Answer the following questions in 6-8 sentences. (i) [(Session 6.2)] Verify the laws of reflection experimentally. CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 176

AS4-Information skills and projects Very Short Answer Type Questions 9. Answer the following questions in one sentence. [Refer to Session 6.2 ] (i) Analyze the table and right your conclusion. S.No. Angle of Angle of Is i=r? incidence of reflection of (Yes/No) 1 light (i) light (r) Yes 2 3 30° 30° 4 45° 45° Yes 60° 60° Yes 75° 75° Yes (ii) In the figure AO and OB are incident ray and reflected ray respectively. <AOB = 90°. Find the values of angle of incidence and angle of reflection? CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 177

Long Answer Type Questions 10. Answer the following questions in 6-8 sentences. (i) [(Session 6.2)] Two plane mirrors are fixed at right angles to each other and an object is placed between them. Trace the path of the rays by which an observer sees the final image in one of the mirrors? CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 178

AS5-Communication through drawing and model making Short Answer Type Questions 11. Answer the following question. (i) [(Session 6.2)] Draw a ray diagram to understand the formation of an image for a pointed object by a plane mirror? Long Answer Type Questions 12. Answer the following question. (i) [(Session 6.3)] Draw the image of a lateral inversion of the letter J. CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 179

AS6-Appreciation and aesthetic sense, Values Short Answer Type Questions 13. Answer the following questions in 3-4 sentences. (i) [(Session 6.2)] Observe the figure. AB and BC are two plane mirrors arranged at 120°. A ray incident at an angle 55° on AB. Find the value of ‘x’? AS7-Application to daily life, concern to bio diversity 180 Short Answer Type Questions CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES

14. Answer the following questions in 3-4 sentences. (i) [(Session 6.3)] Make a solar heater/cooker with plane mirrors and write a report on the process of making. CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 181

Objective Questions AS1-Conceptual Understanding 15. Choose the correct answer. (i) If we increase the size of the hole of the pinhole camera, the image becomes (A) crispy (B) focused (C) blurred (D)can’t say anything (ii) The imaginary line which is perpendicular to the reflecting surface is (A) plane of reflection (B) normal (C)incident ray (D)reflected ray (iii) According to the laws of reflection: (B) Incident angle >Reflected angle (A) Incident angle = Reflected angle (C)Reflected angle >Incident angle (D)Incident angle Reflected angle (iv) When light gets reflected from a surface, it selects the path that takes (A) many paths (B) least time (C)a curved line (D)cannot say anything (v) A ray of light falls on a plane mirror with an incident angle of 35°. The angle of reflection is (A) 30° (B) 35° (C) 53° (D) 60° (vi) The image distance and the object distance in case of plane mirror is (A) equal (B) different (C)sometime equal (D)cannot say (vii) A ray of light incidents on a plane mirror at an angle of 90° to the reflecting surface. The angle of reflection is CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 182

(A) 0° (B) 90° (C) 45° (D) 180° AS2-Asking questions and making hypothesis 16. Choose the correct answer. (i) Which of the following letters doesn’t suffer lateral inversion? (A) C (B) O (C) B (D) N AS3-Experimentation and field investigation 17. Choose the correct answer. (i) When light get reflected from a surface, the angle of reflection is equal to: (A) 90° (B) The angle of incident (C)The angle of normal to the reflecting plane (D) 45° (ii) The image formed by a plane mirror is always (A) virtual and erect (B) virtual and inverted (C)real and inverted (D)real and erect AS4-Information skills and projects 18. Choose the correct answer. (i) is used to deposit on glass plates instead of silver. (A) Iron (B) Nickle (C) Aluminium (D) Copper CHAPTER 6. REFLECTION OF LIGHT AT PLANE SURFACES 183

7. COAL AND PETROLEUM SESSION 1 INTRODUCTION AND SOURCES OF MATERIALS 1.1 Mind Map 1. Sources of materials SESSION 1. INTRODUCTION AND SOURCES OF MATERIALS 184

2. Fossil fuels 1.2 Terminology i. Material Science – The branch of science which deals with materials is called material science. SESSION 1. INTRODUCTION AND SOURCES OF MATERIALS 185

ii. Wind Mills – A windmill is a mill that converts the energy of wind into rotational energy by means of vanes called sails or blades. iii. Bio–diesel – Fuel that is made from natural elements such as plants, vegetables, and reusable materials. Biodiesel can be produced from straight vegetable oil, animal oil/fats and waste cooking oils. iv. Fossil Fuel – Fossil fuels are sources of energy that have developed within the earth over millions of years.They are nonrenewable. e.g–Petroleum, Coal etc. 1.3 Key Concepts i. We use various materials to meet our basic needs, some of them are found in nature. ii. Natural resources can be classified into exhaustible and inexhaustible resources. iii. Natural resources: Air, water and wind are the natural resources. iv. Exhaustible resources: The resources which get exhausted and cannot be renewed. v. Inexhaustible resources: The resources which cannot be exhausted – renewable resources. vi. Fossil fuels are formed from the dead remains of organisms under the earth over millions of years. vii. Fossil fuels are exhaustible. 1.4 Reflection on Concepts Q1. [AS7] Why should people look for alternatives to fossil fuels? [Refer to TB page 105 Q5] A. Fossil fuels cause air pollution, greenhouse effect and global warming. They are also exhaustible. Therefore, they need to be replaced in use by other inexhaustible and healthier alternatives. The fossil fuels on earth are ending, we need alternative source of energy to cope up with the increasing demand for energy i.e fuels. Without alternative source of energy the world would be deprived of basic needs such as electricity, potable water and manufactured foods, etc. Q2. [AS1] Name the petrochemical products which are used in agriculture industry. [Refer to TB page 105 Q3] A. One of the m1ost important uses of petroleum is in the production of ammonia to be used as the nitrogen source in agricultural fertilizers. Agriculture also depends on the use of pesticides to ensure consistent, healthy crop yields. Pesticides are almost all produced from oil. In essence, from running farm machinery to fertilizing plants, agriculture is one of the largest users of petroleum based products. SESSION 1. INTRODUCTION AND SOURCES OF MATERIALS 186

1.5 Application of Concepts Q1. [AS2] What will happen if fossil fuels like coal and petroleum are completely exhausted? [Refer to TB page 105 Q2] A. Coal and Petroleum are non–renewable resources, they get exhausted when put to use. It takes millions of years to form these minerals. In today’s world we cannot imagine human life without coal and petroleum products. Coal and petroleum products are used in household sector, industrial sector, electrical sector, transportation sector, etc. making our life easy. But the usage of these products are increasing very fast day–by–day and if we are not serious, very soon these minerals will be exhausted. Human life will be affected very badly if coal and petroleum products get exhausted completely. If such a situation occurs we won’t get proper electricity, transportation will be a great problem, all household items will become very costly, food items will not be available on time, in short the survival of human life will be very difficult. Q2. [AS7] Suggest some alternative ways to save the fuel resources. [Refer to TB page 105 Q6] A. i. We should look out for alternate source of energy like solar energy, wind energy, tidal energy, bio fuels etc to meet our energy demands. ii. Fossil fuels on Earth will not last forever; we need to conserve these fossil fuels. To conserve fossil fuels one can choose to buy a hybrid car. Some of these cars will run on electricity combined with using small amounts of gas. Some hybrid cars just run on electricity. Either way it is a great way for conserving natural resources when it is concerned with fossil fuels. iii. Minimizing the use of natural resources or reducing the consumption of fuel re- sources. iv. Preventing the misuse of fuel resources. SESSION 1. INTRODUCTION AND SOURCES OF MATERIALS 187

1.6 Higher Order Thinking Skills Q1. [AS7] How is biodiversity effected by the excessive use of fossil fuels? [Refer to TB page 105 Q1] A. The use of fossil fuels raises serious environmental concerns. The burning of fossil fuels produces around 21.3 billion tonnes of carbon dioxide (CO2 )per year, but it is es- timated that natural processes can only absorb about half of that amount, so there is a net increase of 10.65 billion tonnes of atmospheric carbon dioxide per year. Carbon dioxide is one of the greenhouse gases that enhances radiative forcing and contributes to global warming, causing the average surface temperature of the Earth to rise in re- sponse, which the vast majority of climate scientists agree will cause major adverse ef- fects. Air pollution is one more thing that is caused by excessive use of fossil fuels because the burning of fossil fuels(Coal, petroleum etc) release harmful gases in addi- tion to green house gases which are harmful to human health and environment. Many paints made from petroleum release toxic products in to air. These toxic products cause a variety of health issues including heart problems, lungs damage, nausea and dizzi- ness. These toxic products also have adverse effect on plants. Moreover oil spills in the sea causing damage to the ecosystem. 1.7 Suggested Projects Q1. [AS4] Burning fuels releases carbon dioxide, a green house gas, which causes climate changes and leads to global warming. Collect information about this through newspa- pers, magazines etc. and prepare report. [Refer to TB page 106 Q1] A. Students’ activity. SESSION 1. INTRODUCTION AND SOURCES OF MATERIALS 188

SESSION 2 COAL, PETROLEUM AND NATURAL GAS 2.1 Mind Map 1. Coal SESSION 2. COAL, PETROLEUM AND NATURAL GAS 189

2. Petroleum SESSION 2. COAL, PETROLEUM AND NATURAL GAS 190

3. Natural Gas SESSION 2. COAL, PETROLEUM AND NATURAL GAS 191

2.2 Terminology i. Coke – A solid fuel made by heating coal in the absence of air so that the volatile components are driven off. ii. Coal gas – A gaseous mixture produced by the destructive distillation of bituminous coal and used as a commercial fuel. iii. Coal tar – A viscous black liquid containing numerous organic compounds that is obtained by the destructive distillation of coal and used as aroofing, waterproofing, and insulating compound and as a raw material for many dyes, drugs, and paints. iv. Carbonisation – Carbonisation is the term for the conversion of an organic substance into carbon or a carbon–containing residue through pyrolysis or destructive distillation. v. Plankton – The small or microscopic organisms that drift or swim weakly in a body of water, including bacteria, diatoms, jellyfish, and various larvae. 2.3 Key Concepts i. Petroleum is formed from the remains of tiny organisms called planktons. ii. Fractional distillation is the separation of a complex mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heat- ing them to the specific temperature at which one or more fractions of the compound will vaporize. iii. Natural gas is a naturally occurring hydrocarbon mixture consisting primarily of methane with other hydrocarbons, carbon dioxide, nitrogen, hydrogen sulphide, etc. iv. Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by refining petroleum. v. The useful substances obtained from petroleum and natural gas are called petro- chemicals. vi. The slow process of conversion of dead vegetation into coal is called carbonisation. vii. Coke, coal tar, coal and gas are the products of coal. 2.4 Reflection on Concepts Q1. [AS1] Explain why petroleum is also called as liquid gold? [Refer to TB page 105 Q2] A. The constituents of petroleum are very useful to us. Because of its high price and value and its economic “need” and great commercial importance petroleum is called liquid gold. SESSION 2. COAL, PETROLEUM AND NATURAL GAS 192

Q2. [AS1] Explain the process of formation of petroleum in Earth. [Refer to TB page 105 Q4] A. Petroleum was formed from the remains of tiny organisms called plankton that were found in the bottom of seas and oceans. Planktons have tiny droplets of oil inside their bodies. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years in absence of air, high tem- perature and high pressure transformed the dead organism into petroleum and natural gas. Q3. [AS5] Draw the diagram of uses of coal and its products. [Refer to TB page 105 Q1] A. SESSION 2. COAL, PETROLEUM AND NATURAL GAS 193

Coke Coal tar Coal gas Manufacture of Naphthalene Lighting, fuel in steel, extraction of preparation, industries. metals. perfumes, roofing materials, photographic metals, synthetic fibres, paints, explosives, medicines, pesticides, synthetic dyes, construction of roads. 2.5 Application of Concepts Q1. [AS1] Name the petroleum products used for roads surfacing. [Refer to TB page 105 Q1] A. Asphalt and bitumen. Q2. [AS5] Collect information about places where you get coal, petroleum and natural gas in India and mark the places on an outline map of India . [Refer to TB page 105 Q3] SESSION 2. COAL, PETROLEUM AND NATURAL GAS 194

A. Q3. [AS7] How would you appreciate the efforts of human beings to discover an alternate energy source like coal and petroleum for their daily use? [Refer to TB page 105 Q5] A. It is highly appreciable that humans discovered alternate energy source like coal and petroleum for the human needs. It helped a lot for the development. SESSION 2. COAL, PETROLEUM AND NATURAL GAS 195

Coal and petroleum are exhaustible resources. These are the resources that are widely used in our daily life. Earlier people used kiln using wood for cooking food and for travelling they used horses and bullock carts. There was no electricity, so their life was miserable. The wood they were using produced lot of pollution. So they required a fuel not only for cooking purpose but also travelling long distances. In 19th century, the use of coal as fuel was the major thing in development of human beings. Steam engine which used coal was invented during industrial revolution. The petroleum was started as fuel in in 1859 then it was used everywhere in the world because it was better fuel than coal and less pollutant. To meet future energy needs scientists are working for alternate energy sources. Bio–fuel is one of the alternate resources which is renewable. Scientists have also developed methods to harness solar energy, wind energy, tidal energy etc. Q4. [AS7] Assume if you are a driver what measures would you take to save petrol and diesel? [Refer to TB page 105 Q4] A. i. Turning off vehicle regularly. ii. Driving at economical speed. iii. Stopping engine at signals and during waiting period. iv. Ensuring correct pressure in tyres. v. Ensuring regular maintenance of vehicle. 2.6 Higher Order Thinking Skills Q1. [AS7] “Crude oil and refined fuel when spills into the sea from tanker or ships by ac- cident.” Discuss the consequences of this on the environment. [Refer to TB page 105 Q2] A. Crude oil and refined fuel spills from tanker or ships by accident cause damage to natural ecosystem. This can kill sea birds, mammals, shell–fish and other organisms iving in seas. SESSION 2. COAL, PETROLEUM AND NATURAL GAS 196

CONSEQUENCES: Thousands of birds, fishes, sea animals and seals die due to spilling of oil which pollute the natural ecosystem of sea or ocean. About 2 million tonnes of oil spills into the sea every year from oil tankers, mostly during collisions or other accidents. When oil is discharged into the sea and washed up on shorelines they harm many birds and creatures. 2.7 Suggested Experiments Q1. [AS3] Conduct an experiment to show that when we heat high quality coal, a gas evolves which can be burnt. [Refer to TB page 106 Q1] A. Aim: To show that when we heat high quality coal (carbon content is more), a gas evolves which can be burnt. Materials required: Two boiling tubes, Rubber corks, iron stands, delivery tube, jet tube, Bunsen burner. Procedure: i. Take a spoon of powdered coal into a hard boiling tube and fix it to a stand as shown in the figure. ii. Close the test tube with a rubber cork and connect it to another boiling tube which is partially filled with water and has fixed to other stand, with the help of ‘U’ shaped delivery tube as shown in the figure given below. iii. Arrange a jet tube to the cork of second boiling tube. iv. Heat the boiling tube containing coal strongly with the help of Bunsen burner. SESSION 2. COAL, PETROLEUM AND NATURAL GAS 197

Observation : You may notice that the brownish black vapours evolve in the first boiling tube. These vapours are passed through water in the second boiling tube. Colourless gas bubbles evolve from the water. If you burn the gas that is evolving through the jet tube, you can witness a bright flame at the nozzle. This shows when we heat high quality coal, a gas evolves which can be burnt . 2.8 Suggested Projects Q1. [AS4] Compare a CNG run vehicle with that of a diesel run vehicle. What differences do you notice in both cases with respect to pollutants released, level of pollution and cost of fuel? Prepare a report on your findings. You can take the help of a driver to make a report on your observations. [Refer to TB page 106 Q2] SESSION 2. COAL, PETROLEUM AND NATURAL GAS 198