Acoustics

Samacheer Book Back Questions And Answers For Science Standard 10 “Acoustics“

I. Choose the correct 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

2. Velocity of sound in a gaseous medium is 330 ms^–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 ms^-1
c) 156 ms^–1
d) 990 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

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

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

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

II. Fill up the blanks:
1. Rapid back and forth motion of a particle about its mean position is called _____.
2. If the energy in a longitudinal wave travels from south to north, the particles of the medium would be vibrating in _____.
3. A whistle giving out a sound of frequency 450 Hz, approaches a stationary observer at a speed of 33 m s^–1. The frequency heard by the observer is (speed of sound = 330 ms^–1) _____.
4. A source of sound is travelling with a velocity 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 _____.

Answers:
1. Vibration
2. both north and south
3. 500 Hz
4. 2068 Hz

III. True or false: (If false give the reason)
1. Sound can travel through solids, gases, liquids and even vacuum.
2. Waves created by Earthquake are Infrasonic.
3. The velocity of sound is independent of temperature.
4. The Velocity of sound is high in gases than liquids.

Answers:
1. False (Sound waves cannot travel through vacuum)
2. True
3. False (The velocity of sound is dependent of temperature)
4. False (The velocity of sound is high in liquids than gases)

IV. Match the following:
1. Infrasonic                       A. Compressions
2. Echo                               B. 22 kHz
3. Ultrasonic                      C. 10 Hz
4. High pressure region    D. Ultrasonography

Answers:
1. C
2. D
3. B
4. A

V. Assertion and Reason Questions:
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
a. If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
b. If both the assertion and the reason are true but the reason is not the correct explanation of the assertion.
c. Assertion is true, but the reason is false.
d. 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.
a. If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
b. If both the assertion and the reason are true but the reason is not the correct explanation of the assertion.
c. Assertion is true, but the reason is false.
d. Assertion is false, but the reason is true.

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