10th Science Book Back Answers Unit 5 – Acoustics:

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Samacheer Kalvi 10th Science Book Back Answers Physics Unit 5 – Acoustics:

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10th Science – Physics

Unit 5: Acoustics

I. Choose the best answer:

1. When a sound wave travels through air, the air particles
a) vibrate along the direction of the wave motion
b) vibrate but not in any fixed direction
c) vibrate perpendicular to the direction of the wave motion
d) do not vibrate
Ans : (a) vibrate along the direction of the wave motion

2. Velocity of sound in a gaseous medium is 330 m s–1. If the pressure is increased by 4 times without causing a change in the temperature, the velocity of sound in the gas is
a) 330 ms–1   b) 660 ms1    c) 156 ms–1    d) 990 ms–1
Ans : (a) 330 ms–1

3. The frequency, which is audible to the human ear is
a) 50 kHz   b) 20 kHz   c) 15000 kHz    d). 10000 kHz
Ans : (b) 20 kHz

4. The velocity of sound in air at a particular temperature is 330 m s–1. What will be its value when the temperature is doubled and the pressure is halved?
a) 330 ms–1   b) 165 ms–1   c) 330 × 2 ms–1    d) 320 / 2 ms–1
Ans : (c) 330 × 2

5. If a sound wave travels with a frequency of 1.25 × 104 Hz at 344 m s–1, the wavelength will be
a) 27.52 m    b) 275.2 m    c) 0.02752 m    d) 2.752 m
Ans : (c) 0.02752 m

6. The sound waves are reflected from an obstacle into the same medium from which they were incident.
Which of the following changes?
a) speed   b) frequency    c) wavelength    d) None of these
Ans : (d) None of these

7. Velocity of sound in the atmosphere of a planet is 500 m s–1. The minimum distance between the sources of sound and the obstacle to hear the echo, should be
a) 17 m    b) 20 m    c) 25 m   d) 50 m
Ans : (c) 25 m

II. Fill in the blanks:
1. Rapid back-and-forth motion of a particle about its mean position is called _____.
Ans: vibration

2. If the energy in a longitudinal wave travels from south to north, the particles of the medium would be vibrating
Ans: Both North and South

3. A whistle giving out a sound of frequency 450 Hz, approaches a stationary observer at a speed of 33 ms–1. The frequency heard by the observer is (speed of sound = 330 ms–1)
 Ans: 500 Hz

4. A source of sound is travelling with a velocity of 40 km/h towards an observer and emits a sound of frequency 2000 Hz. If the velocity of sound is 1220 km/h, then the apparent frequency heard by the observer is _____.
Ans: 2068 Hz

III. True or False (Correct the Statement if it is false)

1. Sound can travel through solids, gases, liquids, and even vacuum.
Ans: False. Sound can travel through solids, gases, and liquids and cannot through a vacuum.

2. Waves created by Earth Quake are Infrasonic. Ans: True.

3. The velocity of sound is independent of temperature.
Ans: False. The velocity of sound is dependent of temperature.

4. The Velocity of sound is high in gases than liquids.
Ans: False. The Velocity of sound is less in gases than liquids.

IV. Match the following:

Question

Answer:
1. (c) 10 Hz
2. (d) Ultrasonography
3. (b) 22 kHz
4. (a) Compressions

V. Assertion and Reason
Mark the correct choice as

i) If Both the assertion and the reason are true and the reason is the correct explanation of assertion.
ii) If Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
iii) Assertion is true, but the reason is false.
iv) Assertion is false, but the reason is true.

1. Assertion: The change in air pressure affects the speed of sound.
Reason: The speed of sound in a gas is proportional to the square of the pressure.
Ans : (iv) Assertion is false, but the reason is true

2. Assertion: Sound travels faster in solids than in gases.
Reason: Solid posses a greater density than that of gases.
Ans : (ii) If both the assertion and the reason are true and the reason is not the correct explanation of the assertion.

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