Chapter-14
Sound
Learning Card-1
Choose the correct answer:
1. The device which uses ultrasound waves to measure the distance of an object is
a) radar b) scanner c) sonar d) spectra scope
2. A normal human ear can hear sound waves of frequencies
a) less that 20HZ b) greater than 20,000HZ
c) in the range 20 HZ-2000HZ d) greater than 400,000HZ
3. Which of these animals can hear ultrasound?
a. birds b. man c) bat d) ant
4. A sonar uses
a) Infrasonic waves b) audible waves c) ultrasound waves d. Radio waves
5. ECG stands for
a. Electro cardio gram b. Echocardiogram
c. electronic cardiograph d. Electro encephalogram
Answer the Following Questions
1. Why is study of sound important?
Study of sound helps us to know how speech is produced there by to correct speech impairment.
2. What is an echo?
A Sound heard after reflection from a rigid surface is called Echo.
3. What is persistence of hearing?
The sensation of sound persists in our ear for about 0.15, this is called persistence of hearing.
4. What is the minimum distance from the obstacle to hear a clear echo?
17m
5. Calculate the distance of the obstacle from source of sound if the echo is heard after 4 seconds and velocity of sound in air is 340 ms-1.
d=vt/2
d=(340 x 4) /2
d=680 m
The distance of the obstacle from the source of sound is 680m.
6. When can we here a multiple echo?
If the sound reflects from the number of reflecting surface, then we can hear multiple echo’s.
7. How do we hear thunder?
We hear thunder by the multiple reflections of sound from many reflecting surface of clouds.
8. When is sound produced.
Sound is produced by the vibration of bodies.
9. What is Audible range?
20 HZ to 20000HZ
10. What is infrasonic sound.
sound of frequency less that 20HZ is called infrasonic sound.
11. What is ultrasonic sound?
A sound of frequency greater than 20000 HZ is called ultrasonic sound.
12. Name some animals which can produce ultrasound.
Bats, Dolphins, dogs
13. Name some animals which can here ultrasound.
Bats, Dolphins.
14. Why the energy of ultrasound is high?
Because of high frequency.
15. What is SONAR
Sonar stands for “SOUND NAVIGATION AND RANGING”
16. What are the uses of sonar?
1. To measure depth of sea.
2. To locate underwater objects.
17. Which are the two parts of Sonar?
1. Transmitter 2. Detector
18. What is the function of transmitter in SONAR?
A Transmitter produces ultrasound waves and transmits them in to the water all around.
19. What is the function of detector in SONAR?
A detector reflected ultrasound waves and coverts it to electrical signals.
20. Write the relationship between speed, time and distance of sound waves.
d=vt
d=distance of the object from sonar
v= velocity of ultrasound waves in water
t = time interval between transmission and reception of ultrasound waves.
21. What is ECG?
It is a technique to examine heart by ultrasound waves called Echo cardiogram.
22. Why is ultrasound scanning is preferred over x-rays?
Ultrasound waves are less harmful when compared to x-rays.
23. What is Doppler effect?
The apparent change in the frequency of a sound wave or light wave when there is relative motion between the source and the observe is called Doppler effect.
24. Who discovered Doppler effect?
J.C Doppler.
25. Who showed that radio waves are reflected from metal objects?
Heinrich Hertz.
26. Which instruments is used to detect vehicles crossing speed limit?
Radar Gum.
27. What is the relationship between frequency, wavelength and speed of a wave?
V=fλ
28. List any four uses of ultrasound waves?
1.Study of ultrasound waves through a medium reveals physical properties like elasticity, configuration of atoms.
2. Used to detect cracks and flows in metal moldings
3. Used in mixing of immiscible liquids.
4. used in the manufacturing of alloys.
5. used in dry cleaning.
6. used as insect repellants
7. used in sterilization.
8. used to cure neuralylic and rheumatic pains.
9. used in bloodless surgery.
10. used to break gallstones.
Chapter-14
Sound
Learning Card-2
Choose the correct answer:
1. Which of the following is not an application of Doppler effect?
(a) Estimating the speed of aero planes (b) Detecting vehicles crossing the speed limit
(c) Discovery of double stars (d) Mixing immiscible substances like oil and water
2. Doppler effect on sound is observed as a change in its
(a) Pitch (b) Velocity (c) medium of propagation (d) amplitude
3. A device which uses ultrasonic waves to measure the distance direction and speed of underwater object is
(a) ultrasound scanner (b) sonar (c) transmitter (d) detector
4. Which of the following is true? When celestial bodies are moving away from us
(a) The frequency of light emitted by the body decreases
(b) No Doppler effect due to light is observed
(c) The light emitted by the body appears bluish
(d) Wavelength of light emitted decreases
5. A radar gun works on the principle of:
a) Doppler effect due to light (b) Raman effect
(c) Doppler effect of sound (d) Doppler effect of radio waves
Answer the Following Questions
1. Calculate the minimum distance needed to hear a clear echo. The sensation of sound persists in our ear for about 0.1s. To hear a distinct echo, the time interval between the original sound and the reflected sound must be later or equal to 0.1s
d = ?, t = 0.1s, v = 340ms–1 in air
d=vt/2
d=(340 x 0.1)/2
d=17m
To hear echo distinctly, the reflecting surface should be at a minimum distance of 17m from the listener.
2. How are ultrasound waves produced?
Ultrasound waves are produced by a thin quartz slice is placed between two thin metallic plates. And the metallic plates are connected to an A.C. source of frequency more than 20KHz. When the current flows through the metallic plates the quartz slice vibrates with a frequency more than 20KHz producing ultrasonic sound.
3. How bats fly unearingly during nights?
Bats can produce and here sound of frequency up to 100KHz. The sound produced by flying bats gets reflected from obstacle in front of it. By hearing this reflected sound it can detect the obstacle even during nights.
4. How do you find out cracks in the metal molding using ultrasound waves?
Ultrasound waves are passed through metal moldings and transmitted waves are detected. If there is any defect, the ultrasound gets reflected back showing to defect.
5. A ship sends ultrasound waves, it returns from sea bed and it is detected after 6s. If the speed of ultrasound through sea water is 1.5kms–1. What is the depth of the sea?
t = 6s, v = 1.5kms–1, d = ?
d=vt/2
d=(1.5 x 6 )/2
d= 4.5km
6. A shoal of fish is 2km deep from the surface of water in ocean. If velocity of sound in water is 1.5kms–1 then what is the time taken by ultrasound waves to reach shoal of fish?
d = 2 km, v = 1.5kms–1, t =?
d=vt/2
2=(1.5 x t)/2
t = 2.66sec
7. Ultrasound waves are reflected from a shoal of fish in 2s and from the depth of sea it takes 3s to return then calculate the distance between fish and the ocean bed? (v = 1.5kms–1)
d = ?, t = 2s, v = 1.5kms–1
d = vt/2
d= (1.5 x 2)/2
d=1.5 m
distance of the shoal of fish is 1.5k
d = ?, t = 3s, v = 1.5kms–1
d=vt/2
d=(1.5 x 3)/2
d =2.25km
depth of the sea is 2.25km.
Distance between fish and ocean bed = 2.25 – 1.5 = 0.75km
8. How are ultrasound waves used to see internal organs of the body?
An ultrasound scanner is used to see internal organs of the body. Ultrasound waves are directed towards the area on the body to be scanned.
When there is a change in the tissue density, the waves are reflected. The image of the internal organ is displayed either as a static image or as a movie.
9. How RADAR detects objects in the sky?
Radar transmits radio waves from an antenna and then detects the reflected wave after it bounces off the target. By knowing the speed of radio waves and time taken for the signal to bounce off the object and hit the receiver the distance of the object can be detected.
10. How Radar gun detects speed of vehicles?
The radio waves from the radar gun are sent in the direction of the speeding vehicle and the reflected waves are received. The change in the frequency of the incident and the reflected waves help to determine the speed of the speeding vehicle
Chapter-14
Sound
Learning Card-3
Choose the correct answers:
1. A traffic police has to detect the vehicle crossing the speed limit which of the following units is related to the characteristics of the wave used
a) hertz b) parsec c) angstrom d) newton
2. Kiran who is reading in the classroom finds out whether a teacher is coming near the classroom or net even if she cannot see the teacher it is because she.
a) Knows about sonar b) knows about ultrasonics
c) Is aware of doppler effect d) know about frequency and wave length
3. Doppler effect of light can be applied in the study of the following.
a) The velocity of submarines b) Speed of galaxies
c) Pollutants in the atmosphere d) crystal structure
4. The ultrasound signal sent in water by sonar takes 3s to return. It the velocity of sound in water is 1.5km/s the distance travelled by the signal is
a) 2.25km b) 4.5km c) 6km d)9km
5. The technique used in the study of heart diseases is
a) Radar Ranging b)Radiography c) Radar gun d) Echocardiography
Answer the following questions:
1. Can we use ultrasound waves to send messages to satellites? Give reasons.
No, we cannot send ultrasound waves to send messages to satellites. because ultrasound waves need material medium to travel.
2. What property of ultrasound enables it to drill holes through the hard materials?
high frequency and energy
3. Why echoes can’t be heard in a small room
For hearing echo, there should be at least a distance of 17m between the source of sound and the body from which sound is reflected. In small rooms this is not the case, hence echoes are not heard.
4. Two astronauts cannot hear each other on the moon. why?
Material medium is necessary for the propagation of sound. On the moon there is vaccum i.e. no air therefore, sound cannot propagate on the moon.
5. Bats have no eyes still they can as certain distances directions, nature and size of the objects. Explain why?
Bats, have special types of wings, why they fly they produce ultrasonic waves. These waves are received by the cars of bat after they have been reflected by the obiect. The cars of the bat are so sensitive and trained that they not only get information of distance of the obstacle but also nature of reflecting surface.
6. Sound is produced due to a vibratory motion. There why a vibrating pendulum does not produce sound?
The frequency of the vibrating pendulum does not lie within the audible range (20Hz to 20000Hz) and hence it does not produce audible sound.
7. Why A radar is able to detect the reflected waves from an enemy aero plane, after a time interval of 0.02 milliseconds. It the velocity of the waves is 3x108 ms-1, Calculate the distance of the plane from the radar.
Given : t = 0.02 millisecond = 0.02 x 10-3 s
c = 3 x 108 ms-1
d = ?
d = vt /2
d= (3 x 108x 0.02 x 10-3)/2
d= 6000 /2
d= 3000 m
d= 3 km
8. It the sound takes two seconds to reach the boatman, approximately how much time does it take to reach the diver at the same depth? (V = 1450ms-1 t =2s)
Distance travelled by sound in air is = 330x2 = 660 m
If the diver is at the same depth, then the time taken by him will be
t = d/v
t = 660/1450
t = 0.45 s
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