202110244-TRIUMPH-STUDENT-WORKBOOK-PHYSICAL_SCIENCE-G09-PART2

Some of these escaping molecules may be directed back into liquid when they collide with the particles of air. If the number of escaping molecules is greater than the number returned, then the number of molecules in the liquid decreases. Thus when a liquid is exposed to air, the molecules at the surface keep on escaping from the surface till the entire liquid disappears into air. This process is called evaporation. During the process of evaporation, the energy of the molecules inside the liquid de- creases and they slow down. They transfer this energy to escaping molecules during the collisions. “The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation”. Let us determine the reason for faster evaporation of spirit kept under the fan. If air is blown over the liquid surface in an open pan or petri dish, the number of molecules re- turned is reduced to a large extent. This is because any molecule escaping from the surface is blown away from the vicinity of the liquid. This increases the rate of evapora- tion. This is the reason why the spirit in petri dish, that is kept under ceiling fan evapo- rates quickly when compared to that kept closed. We will notice that clothes dry faster when wind is blowing. It means that the temperature of a system falls during evaporation. Evaporation is a surface phenomenon. We can also define evaporation as “The change of phase from liquid to gas that occurs at the surface of the liquid”. It is a cooling process, because the particles of liquid continuously give up their energy to the particles that are escaping from the surface. 3.7 Suggested Projects Q1. [AS4] Observe the evaporation process and write the report in the form of a table for the following. Substances are given in the table for given conditions. [Refer to TB page 209 Q2] Substance Petrol, Kerosene, Alcohol, Water, Conditions Glycerine, Camphor Inside the room, outside the room, exposing to sunlight, out side shadow A. Students’ activity. SESSION 3. EVAPORATION, CONDENSATION, HUMIDITY AND DEW AND... 49

Q2. [AS4] Observe the evaporation process of water which is kept inside, and outside the house and repeatedly do this activity with different shaped dishes. Write the report. [Refer to TB page 209 Q3] A. Students’ activity. Objective Questions (1) Which of the following is a warming process (Pg 208;TB Q 1) (A) Evaporation (B) Condensation (C) Boiling (D)All the above Correct Answer: B SESSION 3. EVAPORATION, CONDENSATION, HUMIDITY AND DEW AND... 50

SESSION 4 BOILING, MELTING, FREEZING 4.1 Mind Map 4.2 Terminology i. Boiling – Boiling is a process in which the liquid phase turns into gaseous phase. ii. Latent Heat of Vaporization –The heat energy required to change 1 g of liquid to gas at constant temperature is called latent heat of vaporization. iii. Melting – The process in which the solid phase changes to liquid phase is called melting. iv. Freezing – The process in which the liquid phase changes to solid phase is called freezing. SESSION 4. BOILING, MELTING, FREEZING 51

4.3 Key Concepts i. “Boiling is a process in which the liquid phase changes to gaseous phase at a constant temperature at a given pressure.” This temperature is called boiling point of the liquid. ii. This heat energy is used to change the state of water from liquid to vapour (gas). This is called latent heat of vapourization. iii. CGS unit of latent heat of vaporization is cal/g and SI unit is J/kg. iv. The process in which solid phase changes to liquid phase at a constant temperature is called melting. This constant temperature is called melting point. v. The Heat energy required to convert 1 g of solid completely into liquid at a constant temperature is called Latent heat of fusion. vi. Latent heat of fusion L = Q/m. The value of Latent heat of fusion of ice is 80 cal/g. vii. “The process in which a substance in liquid phase changes to solid phase by losing some of its energy is called freezing.” viii. Freezing of water takes place at 0°C temperature and at one atmospheric pressure. 4.4 Application of Concepts Q1. [AS1] Answer these –[Refer to TB page 208 Q2] (a) How much energy is transferred when 1 g of boiling water at 100°C condenses to water at 100°C? (b) How much energy is transferred when 1 g of boiling water at 100°C cools to water at 0°C? (c) How much energy is released or absorbed when 1 g of water at 0°C freezes to ice at 0°C? (d) How much energy released or absorbed when 1 g of steam at 100°C cools to ice at 0°C? A. (a) 1 g of boiling water at 100°C condenses to water at 100°C. Heat transferred (Q1 ) = mL = 1x540 SESSION 4. BOILING, MELTING, FREEZING 52

= 540 cal 53 The latent heat of vaporization of water is (L) = 540 cal/g (b) 1 g of boiling water at 100°C cools to water at 0°C Heat transferred (Q2 ) = m.s.∆T = 1x1x100 = 100 cal The latent heat of vaporization of water is (L) = 100 cal/g (c) 1 g of water at 0°C freezes to ice at 0°C Heat transferred (Q3 ) = mL = 1x80 = 80 cal The latent heat of fusion of ice is (L) = 80 cal/g (d) 1 g of steam at 100°C cools to ice at 0°C Heat transferred (Q) = Q1 + Q2 + Q3 = 540+100+80 = 720 cal SESSION 4. BOILING, MELTING, FREEZING

4.5 Suggested Projects Q1. [AS4] Take 2kg of ice is at –5°C. Supply heat continuously to ice till it starts boiling. Note the temperature every minute. Draw a graph between temperature and time using the values you get. What do you understand from the graph? Write the conclusions. (You know that ice melts at 0°C and boils at l00°C. [Refer to TB page 209 Q1] A. Students’ activity. Objective Questions (1) Melting is a process in which solid phase changes to (Pg 208;TB Q 2) (A) Liquid phase (B) Liquid phase at constant temperature (C)Gaseous phase (D)Gaseous phase at constaint temperature Correct Answer: B .(Pg 209;TB Q 6) (2) Boiling point of water at normal atmospheric pressure is (A) 0°C (B) 100°C (C) 110°C (D) –5°C Correct Answer: B (3) When ice melts, its temperature (Pg 209;TB Q 7) (A) Remains constant (B) Increases (C) Decreases (D)Cannot say Correct Answer: A SESSION 4. BOILING, MELTING, FREEZING 54

—— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions 1. State true or false. [Refer to Session 11.1 ] (i) “The average kinetic energy of the molecules is directly proportional to the absolute temperature”. [] 2. Fill in the blanks. [Refer to Session 11.1 ] (i) Heat energy transferred from the body to the body. (ii) Temperature is a measure of the degree of of an object. 3. State true or false. [Refer to Session 11.2 ] (i) Average kinetic energy of particles of a hotter body is greater than that of a colder body. [] (ii) 1 calorie = 4.186 joules. [] 4. Answer the following questions in one sentence. [Refer to Session 11.2 ] (i) Write the definition of “Specific Heat”. CHAPTER 11. HEAT 55

5. State true or false. [] [Refer to Session 11.3 ] [] [] (i) Condensation is a warming process. (ii) Reverse process of evaporation does not take place. (iii) Evaporation takes place at any temperature. 6. Answer the following questions in one sentence. [Refer to Session 11.3 ] (i) Give reason: 1) Evaporation is a cooling process. 7. Fill in the blanks. phenomenon. [Refer to Session 11.3 ] 56 (i) Evaporation is a CHAPTER 11. HEAT

(ii) The heat energy released when water vapour changes to a liquid is called latent heat of . (iii) The process of escaping of molecules from the surface of a liquid at any temperature is called . 8. State true or false. [Refer to Session 11.4 ] (i) Boiling point of a substance depends upon its quantity. [] (ii) Density of water is less than that of ice. [] (iii) On freezing volume of water increases. [] (iv) Temperature measured on Kelvin scale is called absolute temperature. ] [ 9. Answer the following questions in one sentence. [Refer to Session 11.4 ] (i) Why you should always leave little space in the container of water, when you are placing that in deep freezer? CHAPTER 11. HEAT 57

(ii) Give reason: 1. Ice floats on water. Short Answer Type Questions 10. Answer the following questions in 3-4 sentences. (i) [(Session 11.1)] Does transfer of heat take place in all situations? Long Answer Type Questions 11. Answer the following questions in 6-8 sentences. (i) [(Session 11.2)] Why is the specific heat different for different substances? CHAPTER 11. HEAT 58

12. Answer the following questions in 6-8 sentences. (i) [(Session 11.4)] How much energy is released or absorbed when 1 g of steam at 100o c turns to ice at 0o c? CHAPTER 11. HEAT 59

AS2-Asking questions and making hypothesis Short Answer Type Questions 13. Answer the following questions in 3-4 sentences. (i) [(Session 11.4)] Your friend is asked to differentiate between evaporation and boiling. What questions could you ask to make him to know the differences between evapora- tion and boiling? CHAPTER 11. HEAT 60

AS3-Experimentation and field investigation Short Answer Type Questions 14. Answer the following questions in 3-4 sentences. (i) [(Session 11.1)] Write an experiment to show particles move faster in hot water than in cold water. CHAPTER 11. HEAT 61

15. Answer the following questions in 3-4 sentences. (i) [(Session 11.3)] Equal amount of water is taken in two identical circular containers one with radius 3 cm & another with 5 cm, from which container the water evaporate faster? Justify your answer. Long Answer Type Questions 16. Answer the following questions in 6-8 sentences. (i) [(Session 11.3)] Suggest an experiment to prove that the rate of evaporation of a liquid depends on its surface area and vapour that is already present in surrounding air. Write a report. CHAPTER 11. HEAT 62

AS4-Information skills and projects Short Answer Type Questions 17. Answer the following questions in 3-4 sentences. (i) [(Session 11.2)] Analyze the table and answer the following questions. '%&! #
& $'$*      $%%   &$   
)&$   a. Which has the highest specific heat among the substances in the above table? b. Which has the lowest specific heat among the substances in the above table? c. What is the specific heat of the substance in cal/g- o c, whose specific heat is 380 in J/Kg–K? d. What is the specific heat of sea water in J/Kg–K? CHAPTER 11. HEAT 63

AS5-Communication through drawing and model making Short Answer Type Questions 18. Answer the following question. (i) [(Session 11.2)] Draw an experimental setup to show the rate of rise in temperature depends on the nature of the substance. AS6-Appreciation and aesthetic sense, Values Long Answer Type Questions 19. Answer the following questions in 6-8 sentences. (i) [(Session 11.2)] How do you appreciate the role of oceans as “heat store houses” for the Earth ? CHAPTER 11. HEAT 64

AS7-Application to daily life, concern to bio diversity Short Answer Type Questions 20. Answer the following questions in 3-4 sentences. (i) [(Session 11.2)] Appreciate the role of specific heat in keeping a watermelon cool for a longer time after removing it from a fridge on a hot day? CHAPTER 11. HEAT 65

Objective Questions AS1-Conceptual Understanding 21. Choose the correct answer. (i) The average kinetic energy of the molecules is varying with absolute temperature as (A) 1/T2 (B) 1/T (C) T (D) T2 (ii) Which among the following has the highest value of specific heat? (A) Copper (B) Water (C) Mercury (D)Kerosene oil (iii) Rate of evaporation of a liquid depends on (A) its surface area (B) temperature (C)amount of vapour present in the surrounding air (D)all the above (iv) Melting point of ice is (B) 100K (A) 0K (C) 273K (D) 300K (v) The rate of rise in temperature of a substance depends on (A) nature of the substance (B) quantity of the the substance (C)both (A) & (B) (D)neither (A) nor (B) CHAPTER 11. HEAT 66

(vi) SI unit of specific heat is (B) J/kg/K (A) J–kg–K (D) kg/J–K (C) J/kg–K (vii) Boiling point of water at 1 atm (B) 273 oC (A) 100K (D) 373K (C) 3073K (viii) The rise in temperature is high for a substance, if the maximum share of heat energy is utilized for increasing its (A) linear kinetic energy (B) rotational kinetic energy (C)potential energy (D)none of these (ix) What happens to the temperature during evaporation? (A) Falls (B) Rise (C) Constant (D)Not linear (x) When ice melts, its temperature (B) increases (A) remains constant (D)none of these (C) decreases CHAPTER 11. HEAT 67

AS4-Information skills and projects (B) 540 cal/g (D)540 j/kg 22. Choose the correct answer. (i) Latent heat of vaporisation of water is (A) 840 cal/g (C)840 j/kg CHAPTER 11. HEAT 68

12. SOUND SESSION 1 INTRODUCTION AND PROPAGATION OF SOUND 1.1 Mind Map 1.2 Terminology i. Tuning fork – Device to generate particular frequency sound waves. ii. Longitudinal wave – A wave in which the direction of vibration of particles is along the direction of propagation of the wave. iii. Transverse wave – A wave in which the direction of vibration of particles is along the direction perpendicular to that of the propagation of the wave. iv. Compression – High pressure area of a sound wave. v. Rarefaction – Low pressure area of a sound wave. vi. Crest – It is the highest point the medium rises to in a transverse wave. vii. Trough – It is the lowest point the medium sinks to in a transverse wave. 1.3 Key Concepts i. A vibrating body produces sound. ii. Sound is a form of mechanical energy which produces sensation of hearing. iii. A tuning fork is used to produce sounds. It resonates at a constant pitch when set to vibrate. iv. If the particles of a medium move to and fro along the direction of propagation of wave, the wave is called a longitudinal wave. v. Sound travels in the form of longitudinal waves. SESSION 1. INTRODUCTION AND PROPAGATION OF SOUND 69

vi. The region of high density of particles in the medium during propagation of sound is called compression and low density region is called rarefaction. 1.4 Reflection on Concepts Q1. [AS1] What do you understand by a sound wave? [Refer to TB page 228 Q4] A. Sound in air gets propagated in the form of longitudinal wave motion consisting of re- gions of compressions and rarefactions. For example, a tuning fork in a state of vibra- tion. As prong moves towards right, it compresses the layer of air in contact with it. As air has elasticity the compressed air tends to relieve itself of its strain and moves towards the right. In wave form it has been shown in figure. At the point of compression, there is an increase of pressure and is shown in the form of crest C. At the point of rarefaction, the concentration of particles is least. 1.5 Application of Concepts Q1. [AS5] With the help of a diagram describe how compression and rarefaction pulses are produced in air near a source of sound. [Refer to TB page 229 Q4] SESSION 1. INTRODUCTION AND PROPAGATION OF SOUND 70

A. The regions where the coils become closer are called compressions (C) and the regions where the coils are further apart are called rarefactions (R). As we already know, sound propagates in the medium as a series of compressions and rarefactions. Now, we can compare the propagation of disturbance in a slinky with the sound propagation in the medium. These waves are called longitudinal waves. In these waves, the individual particles of the medium move in a direction parallel to the direction of propagation of the disturbance. The particles do not move from one place to another but they simply oscillate back and forth about their position of rest. This is exactly how a sound wave propagates; hence sound waves are longitudinal waves. Objective Questions (1) When can you say that the sound is propagating though a medium (Pg 229;TB Q 1) (A) If the medium is travelling (B) The particles of a medium are travelling (C)When the source of sound is travelling (D)When the disturbance is travelling Correct Answer: D SESSION 1. INTRODUCTION AND PROPAGATION OF SOUND 71

SESSION 2 CHARACTERISTICS OF THE SOUND WAVE 2.1 Mind Map 2.2 Terminology i. Wavelength – The distance between the consecutive compressions or rarefactions. ii. Amplitude – The maximum displacement of a vibrating particle. iii. Frequency – Number of vibrations per seconds. 2.3 Solved Examples Q1. Example 1: Find the time period of the wave whose frequency is 500 Hz. [Refer to TB page 217 ] A. Time period = 1 Frequency T= 1 = 1 s = 0.002 s ν 500 SESSION 2. CHARACTERISTICS OF THE SOUND WAVE 72

Q2. Example 2: In a certain gas, a source produces 40,000 compression and 40,000 rar- efaction pulses in 1 s. When the second compression pulse is produced; the first is 1 cm away from the source. Calculate the wave speed. [Refer to TB page 217] A. We know frequency is equal to number of compression or rarefaction pulses travelled per second, hence frequency (ν ) = 40000 Hz Wave length ( ) = Distance between two consecutive compression or rarefaction pulses. = 1 cm From v = ν = 40,000 Hz x 1 cm = 40,000 cm/s = 400 m/s 2.4 Key Concepts i. The distance between two successive compressions or rarefactions is called wave- length. ii. The maximum variation in density or pressure from the main value is called amplitude or the maximum disturbance of particles of a medium from their mean position is called amplitude. iii. The time taken to complete one oscillation in the medium is called time period of wave. iv. The number of oscillations of the medium at a place in unit time is called frequency. v. The distance by which a point on the wave such as a compression or rarefaction travels per unit time is called speed of sound. 2.5 Reflection on Concepts Q1. [AS1] Explain the following terms. [Refer to TB page 228 Q1] (a) Amplitude (b) Wavelength (c) Frequency A. a) Amplitude: Amplitude is the maximum disturbance in the medium on either side of the mean position. It is usually represented by ‘A’ and its SI unit is metre. b) Wavelength: The distance between two consecutive compressions or two consec- utive rarefactions is called the wavelength (or) the distance between two consecutive crests or troughs is called wavelength. c) Frequency: The number of waves or oscillations propagated in unit time is called the frequency. SESSION 2. CHARACTERISTICS OF THE SOUND WAVE 73

Q2. [AS1] Write the relation between, wavelength, frequency and speed of sound. [Refer to TB page 228 Q2] A. Let the time period of a vibrating body be T. It means, the vibrating body completes one oscillation in time T. One oscillation of a body is represented by a wave of wavelength ń. Now, wave speed = distance travelled by the wave/ time taken Here distance travelled by the wave = wavelength (ń) Time taken = T Then wave speed = V = λ = λ× 1 T T But, 1 = ν (frequency of the wave) T Therefore, V = λ ν Thus, speed o f wave = wavelength × f requency Q3. [AS1] Define the wavelength of sound waves. How is it related to the frequency and the wave speed? [Refer to TB page 228 Q6] A. Wavelength: The distance between any two consecutive compressions or rarefactions is called wave length. (or) The distance between any two consecutive crests or troughs is called wave length of the wave. The relationship between frequency and time period: Let the time taken for oscillations = 1 sec The time taken for one oosnceilloasticoinllasti=on1v is called the time period (T) and the number of But the time taken for oscillations per second is called the frequency (ν) . Hence Frequency and time period are related as T = 1/ν or ν = 1 T Relation between frequency and wave length with speed of wave; Let the distance travelled by a wave in T seconds = ń metres SESSION 2. CHARACTERISTICS OF THE SOUND WAVE 74

The distance travelled by a wave in 1 second = λ metres––––––(1) T λ Thus by definition, speed of sound wave v = T We know that frequency ν= 1 − − − − − − − − − − − − − − − − − − − −(2) T From equation (1) and (2) we get V = νλ Speed of a sound wave = frequency x wave length 2.6 Application of Concepts Q1. [AS1] Two sources A and B vibrate with the same amplitude. They produce sounds of frequencies 1 kHz and 30 kHz respectively. Which of the two waves will have larger power? [Refer to TB page 228 Q2] A. Though the two sources A and B vibrate with same amplitude and produce equal sound, the one with more frequencies that is 30 kHz has larger power than the 1kHz frequency sound. Because the energy depends on frequency. High frequency means more en- ergy. Objective Questions (1) The unit for the number of waves produced in a second are (Pg 229, Q2) (A) Hertz (B) Joule (C) Metre (D) Pascal Correct Answer: A SESSION 2. CHARACTERISTICS OF THE SOUND WAVE 75

SESSION 3 CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTION OF SOUND 3.1 Mind Map SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 76

3.2 Terminology i. Pitch – Characteristic of sound that is dependent on the frequency. ii. Loudness – Characteristic of sound that is dependent on the amplitude. iii. Quality of sound – Characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. iv. Echo – Reflection of sound that arrives at the listener after a small interval of time of arrival of the original sound. v. Reverberation – The collection of reflected sounds from the surfaces in an enclosure. 3.3 Solved Examples Q1. Example 3: An echo is heard after 0.8 s when a boy fires a cracker, 132 m away from a tall building. Calculate the speed of sound. [Refer to TB page 222] A. Echo time, t = 0.8 s Total distance travelled by sound wave, 2d = 2 × 132 m = 264 m Therefore, speed of sound v = 2d = 264m = 330 m/s t 0.8s 3.4 Key Concepts i. Pitch is a characteristic of sound which distinguishes between a shrill sound and grave sound. ii. The degree of sensation produced on the ear is called loudness. iii. The quality or timbre of sound is the characteristic which enables us to distinguish between musical notes emitted by different musical instruments. iv. A reflection of sound arriving at the listener in more than 0.1 seconds after direct sound is called an echo. v. A reflection of sound arriving at the listener in less than 0.1 seconds after direct sound is called reverberation. 3.5 Reflection on Concepts Q1. [AS7] Why is soft furnishing avoided in concert halls? [Refer to TB page 228 Q5] A. Soft furnishing such as cushioned chairs, thermocol–articles, fluffy material, and door curtains are avoided in concert halls because they are good absorbers of sound. SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 77

3.6 Application of Concepts Q1. [AS1] Does the sound follow same laws of reflection as light does? [Refer to TB page 228 Q1] A. Sound follows reflection, refraction and interference, dispersion just as light. But sound waves are longitudinal waves where as light waves are electromagnetic waves, which can travel even though vacuum. Q2. [AS7] How are multiple reflections of sound helpful to doctors and engineers? [Refer to TB page 229 Q5] A. Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs. In stethoscopes the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflections and by amplifying the sound. Doctors can see the images of patient’s organ like liver, gall bladder, uterus etc. to know the abnormalities in their functioning using ultrasounds. Engineers use the reflection of sound in designing concert halls and theatre halls. 3.7 Higher Order Thinking Skills Q1. [AS6] How do you appreciate efforts of a musician to produce melodious sound using a musical instrument by simultaneously controlling the frequency and amplitude of the sounds produced by it? [Refer to TB page 229 Q2] A. i. The sounds which produce a pleasing effect on the ear are called musical sounds. ii. Any instrument which produces musical sound is called musical instrument. iii. The person who plays a musical instrument to produce melodious sound is called a musician. iv. The musician must have control on breathing, concentration on the output of the sound, which is a very hard task. SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 78

v.The quality of sound is that characteristic of a sound which enables us to distinguish between musical notes emitted by different musical instruments or voices even though they have same pitch and loudness. Pitch depends on frequency and loudness depends on amplitude. By simultaneously controlling frequency and amplitude the musician can vary quality and produce melodious notes. The musician should have control over this. vi. For this, the musician need a lot of practice. vii. With the musician’s practice and knowledge over musical notes only we can hear melodious sound, otherwise it could only be a noise. Hence the efforts of musician are highly appreciable. Q2. [AS7] How do echoes in a normal room affect the quality of the sounds that we hear? [Refer to TB page 229 Q3] A. Room acoustics refer to the quality of sound maintained in the room, and they can affect your ability to hear effectively. Sound waves bounce off hard surface like windows, walls and hard floors. This creates sound reflections and echoes (called “reverberation”). The result of excess reverberation is distorted speech. Large gyms, cathedrals, and open marble lobbies quickly come to mind when we think about reverberation. Reverberation can also occur in smaller spaces such as classrooms. We’ve all experienced how much easier it is to hear in rooms that are carpeted and have upholstered furniture (which absorbs noise) than in empty rooms with tile or cement floors. Any one of these conditions (distance, noise or reverberation) can create listening prob- lems. More often than not, they occur together and have a debilitating effect on the ability to hear and process speech. HATS can help you overcome these listening difficulties. 3.8 Suggested Experiments Q1. [AS3] Conduct an experiment to listen the reflected sound and write a report. [Refer to TB page 230 Q1] SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 79

A. i. Take two long, identical tubes and place them on a table near a wall. ii. Ask your friend to speak softly into one tube while you use the other tube to listen. iii. Adjust the tube until you hear the best sound. iv. You will find that you hear your friend’s voice best when the tube makes equal angles with a normal to the wall. v. This shows that reflection of sound follows the same as the reflection of light. vi. Lift your tube slightly above the table. vii. You will not be able to listen the voice clearly, because the plane carrying the incident sound, pipe carrying reflected sound will not be in the same plane. viii. Repeat the experiment by placing flat objects of different materials (steel and plas- tic trays, a card board, a tray wrapped with cloth etc.) against the wall. Observe the changes in the sound. Observations: i. Reflection of sound follows the laws of reflection of light. ii. When the plane carrying incident wave and reflecting wave changes, the reflected sound cannot be heard clearly. iii. Hard or rough surfaces reflect the sound better, than soft surfaces. 3.9 Suggested Projects Q1. [AS7] “We know that sound is a form of energy. So, the large amount of energy produced due to the sound pollution in cosmopolitan cities can be used to our day to day needs of energy. It also helps us to protect bio diversity in urban areas.” Do you agree with this statement? If yes explain. [Refer to TB page 230 Q2] SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 80

A. 1. Sound is a form of energy. The large amount of energy produced due to sound pollution in cosmopolitan cities can assure us to meet the energy crisis in the world to some extent. 2. This sound energy originating from motor vehicles, jet planes and locomotives can be harnessed and used for converting into mechanical energy. This mechanical energy can be used to turn electric generators and electricity can be produced. 3. This electrical energy can be utilized in several ways. 4. Pitch depends on frequency and loudness depends on amplitude. By simultane- ously controlling frequency and amplitude the musician can vary quality and produce melodious notes. Objective Questions (1) The characteristic feature of sound which conveys the sensation of sound to our brain is (Pg 230, Q5) (A) Pitch (B) Loudness (C) Quality (D) Amplitude Correct Answer: A SESSION 3. CHARACTERISTICS OF A MUSICAL SOUND AND REFLECTI... 81

SESSION 4 RANGE OF HEARING AND APPLICATIONS OF ULTRASOUND 4.1 Mind Map SESSION 4. RANGE OF HEARING AND APPLICATIONS OF ULTRASOUND 82

4.2 Terminology i. Infrasonic sound – Sound of frequencies less than 20 Hz. ii. Sonic –Relating to a sound wave. iii. Ultrasonic sound – Sound of frequencies greater than 20 kHz. iv. Sonar – Sound Navigation And Ranging; a technique used to detect objects under water using sound waves. 4.3 Solved Examples Q1. Example 4: A research team sends a sonar signal to confirm the depth of a sea. They heard an echo after 6s. Find the depth of the sea, if the speed of sound in sea water is 1500. [Refer to TB page 226] A. Let the depth of the sea = d m Then total distance travelled by sonar signal (s) = 2d Speed of sound in sea water (u) = 1500 m/s Total time taken (t) = 6s From, s = ut, 2d = 1500 m/s x 6s ⇒ d = 9000 m = 4.5 km 2 4.4 Key Concepts i. The audible limit of human beings is usually 20 Hz to 20 kHz. ii. Sound of the frequency less than 20 Hz is called infrasonic sound. iii. Sound of the frequency higher than 20 kHz is known as ultrasonic sound. 4.5 Reflection on Concepts Q1. [AS2] Which has larger frequency –infrasonic sound or ultrasonic sound? [Refer to TB page 228 Q3] SESSION 4. RANGE OF HEARING AND APPLICATIONS OF ULTRASOUND 83

A. Ultrasonic have larger frequency than infrasonic. The frequency of ultrasonic is higher than 20 kHz. The frequency of infrasonic is less than 20 Hz. 4.6 Application of Concepts Q1. [AS2] You might have observed that sometimes your pet dog starts barking though no one is seen near in its surroundings or no disturbance heard nearby. What questions would you have in your mind about the peculiar behaviour of dog after your understand- ing about ‘range of hearing of sound’? [Refer to TB page 228 Q3] A. Dogs can hear ultrasonic sound up to a frequency of 50,000 Hz. Hence when a dog barks we may not see anyone nearby but the pet dog might have heard a stranger at a distance whom we can’t perceive and so it starts behaving peculiarly. 4.7 Higher Order Thinking Skills Q1. [AS1] Explain the working and applications of SONAR. [Refer to TB page 229 Q1] A. SONAR stands for Sound Navigation and Ranging; i. This is a method for detecting and finding the distance of objects under water by means of reflected ultrasonic waves. The device used in this method is also called SONAR. ii. SONAR system consists of a transmitter and a detector which are installed in the ‘Observation centre’ on the board of a ship. iii. From the observation centre on the frequencies, say 1,000 kHz, are sent in all directions into the water through transmitter. These waves travel in straight lines till they hit an object such as a submarine, sunken ship, a school of fish etc. The waves are then reflected and are received back by the receiver at the observation centre. The direction from which a reflected wave comes to the observation centre tells the direction in which the object is located. iv. From the time between sending the ultrasonic waves and receiving its echo and the speed of sound in sea water, the distance of the object from the observation center is calculated. Reflections from various angles can be utilized to determine the shape and size of the object. v. Let ‘d’ be the distance between the sonar and an underwater object, ‘t’ be time between sending an ultrasonic wave and receiving its echo from the object and ‘u’ is the speed of sound in water. The total distance covered by the wave from the sonar to the object and back is 2d. SESSION 4. RANGE OF HEARING AND APPLICATIONS OF ULTRASOUND 84

Using s = ut, or 2d = ut Application: Marine geologists use this method to determine the depth of sea and and to locate underwater hills and valleys. 4.8 Suggested Projects Q1. [AS4] Collect the information about the animals which communicate through Infrason- ics or ultrasonics. Collect their pictures and write a report on their communication tech- nique. [Refer to TB page 230 Q1] A. Students’ activity. Objective Questions (1) The sounds of frequency less than 20 Hz are known as (Pg 229, Q3) (A) Ultra sounds (B) Soft sounds (C)Louder sounds (D) Infrasonics Correct Answer: D (2) The sound limit between the frequency of 20Hz – 20000Hz is called as (Pg 229, Q4) (A) Audible range (B) Ultra sound range (C)Low sound range (D) Supersonics Correct Answer: A 85 SESSION 4. RANGE OF HEARING AND APPLICATIONS OF ULTRASOUND

—— CCE Based Practice Questions —— AS1-Conceptual Understanding Very Short Answer Type Questions 1. Match the following. [(Session 12.4)] Column A [] Column B i. Drilling holes a. Breaking kidney stones ii. Ultrasonic cleaning [ ] b. Glass iii. Ultrasonic detection [ ] c. Imaging of organs and foetus iv. Ultrasonography [ ] d. Dresses and utensils v. Ultrasound surgery [ ] e. Metal rods and construction materials 2. Answer the following questions in one sentence. [Refer to Session 12.4 ] (i) What is the range of frequency of sound that the human ear can hear? (ii) Name the technique which uses ultrasonic waves to form an image of the heart. (iii) What does SONAR stand for? 86 CHAPTER 12. SOUND

(iv) What is the use of SONAR? (v) What do you call sound of frequency less than 20 Hz? 3. State true or false. [Refer to Session 12.3 ] (i) Laws of reflection of sound are different from the laws of reflection of light. ] [ (ii) Hard surfaces reflect sound better than soft surfaces. [] (iii) Reflected sound arriving at the position of listener more than 0.1 s after the direct sound is called reverberation. [] (iv) Pitch distinguishes between a shrill sound and a growling sound. [ ] (v) Incident sound and reflected sound make unequal angles with the normal. ] [ CHAPTER 12. SOUND 87

4. Answer the following questions in one sentence. [Refer to Session 12.3 ] (i) What are the characteristics by which we can distinguish a musical note? (ii) When is the pitch of a musical note said to be high? 88 (iii) What is loudness? (iv) What happens if the peak of a sound wave is high? (v) In what units is loudness of sound measured? 5. Fill in the blanks. [Refer to Session 12.3 ] CHAPTER 12. SOUND

(i) Stethoscope works on the principle of reflections of sound. (ii) If reflected sound reaches our ears in less than 0.1 s, then it is known as a . (iii) To reduce the echo in auditoriums, walls are covered with materials. (iv) In horns, conical surface helps to guide the . (v) Music arises through guitar because of vibration of . 6. Answer the following questions in one sentence. [Refer to Session 12.2 ] (i) What four quantities describe the nature of the wave? (ii) What happens to density and pressure of air when sound travels through it? (iii) During a thunderstorm why do you think we first see the flash and then hear sound? (iv) In whose honour was the SI unit of frequency, Hertz, given? 89 CHAPTER 12. SOUND

(v) If a noise is made in an open atmosphere and in water, in which case is the sound heard first? 7. Fill in the blanks. [Refer to Session 12.2 ] (i) The distance between two consecutive crests or troughs is denoted by _________. (ii) Frequency of the sound wave is denoted as . (iii) Speed of a sound wave = . (iv) Sound travels fastest in media. (v) Unit of amplitude in terms of pressure is . 8. Fill in the blanks. [Refer to Session 12.1 ] (i) Sound is produced by bodies. (ii) Sound is a form of . (iii) Pulse of a vibrating string where the density of air is more is known as . (iv) Pulse of a vibrating string where the density of air is less is known as . (v) If the particles of medium vibrate along the direction of wave, the wave is known as . CHAPTER 12. SOUND 90

Short Answer Type Questions 9. Answer the following questions in 3-4 sentences. (i) [(Session 12.4)] List out the industrial applications of ultrasonic waves. (ii) [(Session 12.4)] A research team sends a SONAR signal to confirm depth of sea. They heard an echo after 10 s. Find the depth of sea water. (Speed of sound in water is 1500 m/s.) 10. Answer the following questions in 3-4 sentences. 91 (i) [(Session 12.3)] What do you mean by pitch? CHAPTER 12. SOUND

(ii) [(Session 12.3)] An echo is heard 0.75 s after a boy shouts from a distance of 150 m away from a building. Calculate the speed of sound. 11. Answer the following questions in 3-4 sentences. (i) [(Session 12.2)] What is the wavelength of a sound wave? CHAPTER 12. SOUND 92

(ii) [(Session 12.2)] On what basis is the loudness of sound determined? 12. Answer the following questions in 3-4 sentences. (i) [(Session 12.1)] How does sound travel from source to our ears? (ii) [(Session 12.1)] Define longitudinal and transverse waves. How do they affect the medium? CHAPTER 12. SOUND 93

Long Answer Type Questions 13. Answer the following questions in 6-8 sentences. (i) [(Session 12.4)] Explain the working of SONAR. CHAPTER 12. SOUND 94

14. Answer the following questions in 6-8 sentences. (i) [(Session 12.3)] What is the difference between a reverberation and an echo? 15. Answer the following questions in 6-8 sentences. (i) [(Session 12.2)] In hydrogen gas, a tuning fork produces 25,000 compressions and 25,000 rarefactions in 1 s. When the second compression pulse is produced, the first is 1 cm away from the source. Calculate wave speed. AS2-Asking questions and making hypothesis 95 Short Answer Type Questions CHAPTER 12. SOUND

16. Answer the following questions in 3-4 sentences. (i) [(Session 12.3)] We can distinguish the musical notes produced by different musical instruments though they have same pitch and loudness. How do you think we can identify that? AS3-Experimentation and field investigation Short Answer Type Questions 17. Answer the following questions in 3-4 sentences. (i) [(Session 12.1)] Write an activity to show sound is a form of energy. CHAPTER 12. SOUND 96

AS4-Information skills and projects Short Answer Type Questions 18. Answer the following questions in 3-4 sentences. (i) [(Session 12.3)] Complete the table. S.No. Characteristic of sound The property that varies 1 Frequency 2 Loudness CHAPTER 12. SOUND 97

AS5-Communication through drawing and model making Long Answer Type Questions 19. Answer the following question. (i) [(Session 12.1)] Draw the diagram showing compressions and rarefactions of a vibrat- ing membrane. AS6-Appreciation and aesthetic sense, Values Long Answer Type Questions 20. Answer the following questions in 6-8 sentences. (i) [(Session 12.3)] How do you appreciate the uses of sound? CHAPTER 12. SOUND 98