CHAPTER-14
SOUND
Text Book Question and Answers
I. Four alternatives are given to each of the incomplete statements/questions. Choose the answer
1. Echo of sound is due to ------- of sound
(a)propagation (b)reflection (c)refraction (d)speed
Answer: (b)reflection
2. The property of ultrasonic waves used in manufacturing emulsion for photographic films is its,
(a)high speed (b)high frequency (c)higher wavelength (d)high amplitude.
Answer: (b)high frequency
3. When a source emits light of particular wavelength and the source is moving away from us, the wavelength appears
(a)longer (b)first longer and then shorter (c)unaltered (d)shorter
Answer: (a)longer
4. The audible range in humans is
(a)20 Hz to 2000 Hz (b)200 Hz to 20,000 Hz (c)20 Hz to 20,000 Hz (d)200 Hz to 20 KHz.
Answer: (c)20 Hz to 20,000 Hz
5. The speed of ultrasonic sound in air is
(a)3 x 108 m s-1 (b)340 m s-1 (c)1500 m s-1 (d)4500 m s-1
Answer: (b)340 m s-1
II. Complete the following statements
1. The sound wave is of the type Longitudinal waves
2. Ultrasonic is preferred to X-ray in medical field because less harmful or high frequency
3. When ultrasound is used to examine heart, it is called Echocardiography(ECG)
4. The shift caused in visible spectrum of light emitted by galaxies is Red shift
III. Match the following
1. Radar – electromagnetic radiation
2. Sonar - ultrasound
3. Doppler Effect – apparent shift in frequency
IV. Answer the following questions
1. What is an echo? Mention the condition for the echo to be heard.
The sound heard after reflection from a rigid surface is called echo.
The conditions for the echo to be heard are.
i. To hear a distinct echo the time interval between the original sound and the reflected sound must be later or equal to 0.1 sec.
ii. The reflecting surface should be at a minimum distance of 17m from the listener.
2. An ultrasonic sound sent from a ship travels with the speed 1530 ms-1 is sea water. How deep is the water if the time delay of the echo from the sea bed is 6 s?
Data:
v=1530 ms-1
t= 6 sec.
d=?
Solution:
v= 2d/t
d= vt/2
d=( 1530 x 6 )/2
d= 4590 m
3. What is SONAR? How does it work?
SONAR stands for Sound Navigation and Ranging. This is a device which uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
Sonar consists of a transmitter and a detector in a boat.
The transmitter produces and transmits ultrasonic waves which travel through water until they strike an object. They get reflected and the reflected wave return to the SONAR and are sensed by the detector. The time interval between transmission and reception is recorded. The distance of the object is calculated.
4. What is Doppler Effect? Explain with an example.
Doppler Effect is the apparent change in frequency of wave motion due to the relative motion between the source and the observer.
Example: A person standing on a railway platform feels a change in the pitch of the whistle of a train in motion. A similar change in pitch results when moving observer goes past a stationary sounding horn.
5. Mention three applications of Doppler’s effect.
i. It is used to determine the velocity of submarines.
ii. It is used by traffic authorities to detect vehicles crossing the speed limit.
iii. It is used in tracking artificial satellites.
Additional Questions and Answers
1. List some of the properties of sound,
The following are some of the properties of sound:
· Sound is a form of energy.
· It is produced by the vibration of bodies.
· Sound requires a material medium for its propagation.
· Sound travels in the form of waves.
· Sound undergoes reflection and refraction just the way light does.
· Sound travels through air at a speed of about 330 m s1.
· Sound travels fastest through solids.
2. How is sound produced?
Sound is produced by the vibration of bodies.
3. Give the relationship between frequency (f), wavelength (l) and velocity (v) of a wave in the form of an equation.
The relationship between frequency (f), wavelength (l) and velocity (v) of a wave is given by the equation v = f l
4. What is an echo? How is it caused?
A sound caused by the reflection of sound waves from a surface back to the listener is called an echo.
Echo is the direct result of reflection of sound.
5. What should be the minimum distance between the listener and the reflecting surface to hear an echo clearly?
To hear an echo distinctly, the reflecting surface must be at a minimum distance of 17 m from the listener.
6. What are multiple echoes due to? Give an example for multiple echoes.
Multiple echoes are due to multiple reflections of sound from a number of reflecting surfaces.
The whispering gallery of Golgumbuz at Bijapur produces a sound seven times. This is an instance of multiple echoes.
7. What is audible sound? What is its frequency range?
Sound which can be heard by human ears is called audible sound. The frequency range of audible sound is 20 hertz to 20000 hertz
8. What are ultrasonic sounds?
Sounds of frequency beyond 20khz are called ultrasonic sounds.
9. What is the range of their frequency and wavelength?
The range of ultrasonic sound is from 20 kHz to 5 x 105 kHz. The range of wavelength sound is from 1.65 cm to about 6 x 10-5 cm.
10. What is ultrasonics?
The branch of science that deals with the study of ultrasound is called ultrasonics.
11. What are infrasonic sounds?
Sounds of frequency below 20hz are called infrasonic sounds. They are also called subsonic sounds.
12. Why do ultrasonic waves have high energy?
The energy of a wave is proportional to its frequency. Ultrasonic waves have high energy because their frequency is quite high.
13. How to produced ultrasonic sound.
Take a thin quartz slice. Place it between two thin metallic plates as shown in the figure. Connect the metallic plates to a 220 kHz A.C. source. When current flows through the metallic plates, the quartz slice begins to vibrate producing sound waves of frequency more than 20 kHz. These waves are ultrasonic sound waves.
14. List the uses of ultrasonic waves.
i. They are used in dry-cleaning clothes
ii. They are used as insect repellents and to kill bacteria
iii. They are used to detect cracks and flaws in metal mouldings
iv. They are used to break gallstones and kidney stones
v. They are used to treat neuralgic and rheumatic pains
vi. They are used for welding. local heating and in drilling small holes in hard materials.
vii. They are used in bloodless surgery. They are used for welding.
viii. They are also used to study the properties of a medium such as elasticity, configuration of atoms etc.
ix. They are used in SONAR devices.
x. They are used in ultrasonic scanners.
xi. They are used to prepare homogenized
15. What is an ultrasound scanner? How does it work? Write the uses and advantages of ultrasound scanner.
Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of human body.
Working of an ultrasound scanner:
i. Ultrasound waves are directed towards the area on the body to be scanned.
ii. When there is a change in density of tissues, the waves are reflected.
iii. The image of the internal organ is displayed either as a static image or as a movie.
iv. Uses of ultrasound scanner:
v. Ultrasound scanning is usually used in examining fluid-filled organs like the kidney, urinary bladder, heart, spinal cord, brain, pancreas etc…
vi. When ultrasound waves are used to examine heart it is called echocardiography. The report obtained is called an Electro Cardiogram
vii. A foetus can be examined safely and checked for growth and other congenital abnormalities using an ultrasound scanner.
viii. An ultrasound scanner is used as a guide during surgery.
Advantages of ultrasound scanning
i. Ultrasound waves are safe and harmless when compared to X-rays
ii. Ultrasound scans are easy to perform
iii. An ultrasound scan gives an idea of the internal organ without surgery.
16. Distinguish between audible sound and ultrasonic sound.| Audible sound | Ultrasonic sound |
| 1) Human ears can recognize this sound. 2) Have frequency in the range of 20 Hz to 20000 Hz. 3) The energy of audible sound is quite less. | 1) Human ears cannot recognize this sound. 2) Have frequency higher than 20000 Hz. 3) Ultrasounds have much higher energy than audible sound. |
17. What is the technique used in Sonar called?
The technique used in Sonar is called echo-ranging.
18. What is red shift?
When a source emits light of particular wave length and the source is moving away from us, the wavelength appears longer to us. The colour of the light is shifted towards the red end of the spectrum. This effect is known as red shift.
19. Define blue shift.
The displacement of spectral lines of light received from a distant galaxy towards shorter wavelengths (the blue end of the spectrum) is called blue shift.
20. Distinguish between blue shift and red shift of galaxies.
| Redshift of galaxy | Blueshift of galaxy |
| 1. Redshift occurs when the galaxy is moving away from us. 1) 2. Redshift of a galaxy is due to an apparent decrease in the frequency of light received from the galaxy. | 1) 1. Blueshift happens when the galaxy is moving towards us. 2) 2. Blueshift of a galaxy is due to an apparent increase in the frequency of light received from the galaxy. |
21. Expand RADAR
Radio Detection and Ranging.
22. What is a Radar?
The technique (device) of determining the presence, direction, distance and speed of an object in space using radio waves is known as radar
23. State the differences between a sonar and a radar
| SONAR | RADAR |
| 1) 1. Is used to determine the position and speed of underwater objects. 2) 2. Employs ultrasonic sound waves. 3) 3. Cannot function in empty space as ultrasound requires a medium for propagation. 4) 4. Has relatively shorter range. | 1. Is used to determine the position and speed of objects in space. · 2. Employs radio waves or microwaves. · 3. Functions even in vacuum as electromagnetic waves do not need a medium for their propagation. · 4. Has relatively longer range. |
24. What is the principle of SONAR?
SONAR works on the principle of echo-ranging.
25. Write a note on medical applications of ultrasound waves.
i. This technique is an invaluable diagnostic tool for examining fluid-filled organs such as the bladders, kidneys and ovaries.
ii. This technique can also be used to examine the arterial system, the heart, the pancreas, the urinary tract, the brain and the spinal cord.
iii. Ultrasound is used to examine the heart; it is called echocardiography (ECG). ECG is used in the diagnosis of heart diseases.
iv. The best known application is the examination of the foetus during pregnancy to detect congenial and growth abnormalities.
v. Ultrasound provides images of the internal organs of a human body.
26. Explain Doppler's effect with an example.
The pitch (frequency) of the whistle of an approaching train appears to increase for an observer standing on a platform. Similarly, the pitch appears to decrease if the train is moving away from the observer. Similar effect is observed if the observer himself is moving with respect to the source. Such effects, are observed in all kinds of waves. From this we may conclude that there is an apparent change in the frequency of the waves due to the relative motion between the source and the observer. The phenomenon is known as Doppler’s effect.
27. Is Doppler's effect applicable to light? When is it observable?
Doppler’s effect is applicable to all kinds of waves including light. The speed of light is so high that only celestial bodies or atomic sources moving at very high velocities show pronounced Doppler’s effect.
28. Mention three applications of Doppler Effect.
i. Doppler Effect in sound can be used to determine the velocity of submarines.
ii. Doppler Effect is used to determine the speed of the vehicle. The instrument used for the purpose is called Radar gun.
iii. Doppler Effect is used in tracking the artificial satellites.
iv. Doppler Effect is used in the study of binary stars, Saturn rings, and galaxies. Doppler Effect is also used to estimate speeds of stars, galaxies, rotation of sun’s disc.
29. Write a note on application of Doppler Effect in astrophysics.
i. Doppler Effect is used in the study of binary stars, Saturn rings, and galaxies.
ii. Doppler Effect is used to estimate speeds of stars, galaxies, rotation of sun’s disc.
30. Using Sonar, ultrasonic waves are emitted at the ocean water surface. These waves are reflected by the ocean bottom. If the time interval between the emission of the waves and the detection of the reflected waves is 3.5 s, find the depth of the ocean.
Velocity of sound in water = 1.5 km/sec.
Distance travelled d = Vt =1.5X3.5 = 5.25km
Depth of ocean d = Vt/2 = 5.25/2 = 2.625 km
31. Mention the uses of SONAR.
i. Sonar is used to find the depth of the ocean.
ii. Sonar is used to locate submarines and icebergs.
32. What kinds of waves are employed in Radar for ranging objects?
Radar employs either radio waves or microwaves for ranging objects in space.
33. Who discovered that radio waves are reflected from metallic objects?
A German scientist Heinrich Hertz discovered in 1886 that metallic objects reflect radio waves.
34. Mention the applications of radar.
Radars are used to track aircrafts, motor vehicles and satellites. Radar is an important tool in weather forecasting and helps make the forecasts more accurate.
35. What is a radar gun? What kind of waves does it employ?
A handheld device used by traffic police to estimate the speed of a passing vehicle is called a radar gun. A radar gun employs radio waves.
36. What is the principle on which a radar gun works?
A radar gun works on the principle of Doppler effect.
37. How does a police radar gun work?
OR
How do traffic authorities identify vehicles which cross the speed limit using Doppler’s effect?
A radar gun works on the principle of Doppler effect. A radar gun is a handheld device which consists of a radio wave transmitter and a receiver. Radio waves of known frequency are sent in the direction of the speeding vehicles and the reflected waves are received. The change in the frequency is used to determine the speed of the vehicle.
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