Acoustics Book Back Questions 10th Science Lesson 5

10th Science Lesson 5

5] Acoustics

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

Acoustical wonder of Golconda fort (Hyderabad, Telangana) : The Clapping portico in Golconda Fort is a series of arches on one side, each smaller than the preceding one. So, a sound wave generated under the dome would get compressed and then bounce back amplified sufficiently to reach a considerable distance.

What is meant by rarer and denser medium? The medium in which the velocity of sound increases compared to other medium is called rarer medium. (Water is rarer compared to air for sound). The medium in which the velocity of sound decreases compared to other medium is called denser medium. (Air is denser compared to water for sound).

Whispering Gallery: One of the famous whispering galleries is in. St. Paul’s cathedral church in London. It is built with elliptically shaped walls. When a person is talking at one focus, his voice can be heard distinctly at the other focus. It is due to the multiple reflections of sound waves from the curved walls.

Whenever there is a relative motion between a source and a listener, the frequency of the sound heard by the listener is different from the original frequency of sound emitted by the source. This is known as “Doppler effect”.

Choose the best answers:

1. When a sound waves 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 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) 20kHz

(c) 15000kHz

(d) 10000kHz

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 ms^-1

(b) 165 ms^-1

(c) 330 x √2 ms^-1

(d) 320 / √2 ms^-1

5. If a sound waves travels with a frequency of 1.25 x 10⁴ Hz at 344 ms^-1, the wave length 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 ms^-1. The minimum distance between the sources of sound and the obstacle to hear the echo, should be

(a) 17 m

(b) 20m

(c) 25m

(d) 50m

Fill in the blanks:

1. Rapid back and forth motion of a particle about its mean position is called _________________.

a. particular movement

b. vibrations

c. molecular movement

d. acoustics

2. If the energy in a longitudinal wave travels from south to north, the particles of the medium would be vibrating in _______________.

a. only north

b. only east

c. both north and south

d. both east and west

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) ____________________.

a. 500 Hz

b. 550 Hz

c. 300 Hz

d. 510 Hz

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 ____________.

a. 2067 Hz

b. 2068 Hz

c. 2065 Hz

d. 2066 Hz

State true or false. If false, correct the statement:

1. Sound can travel through solids, gases, liquids and even vacuum.

2. Waves created by Earth Quake are Infrasonic.

3. The velocity of sound is independent of temperature.

4. The velocity of sound is high in gases than liquids.

Match the following:

1. Infrasonic – compressions

2. Echo – 22 kHz

3. Ultrasonic – 10 Hz

4. High pressure region – ultrasonography

Consider the statements given below and choose the correct option:

Mark the correct choice as

(a) If both assertion and reason are true and reason is the correct explanation of assertion

(b) If both assertion and reason are true but reason is not the correct explanation of assertion

(c) If assertion is true but reason is false

(d) If assertion is false but 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.

2. Assertion: Sound travels faster in solids than in gases.

Reason: Solid posses a greater density than that of gases.

Answers:

Choose the best answers:

1.Vibrate along the direction of the wave motion 2. 330 ms^-1 3. 20Hz 4. 330 ms^-1 5.0.02752m 6. None of these 7. 25m

Fill in the Blanks:

1.Vibrations 2. Both north and south 3. 500 Hz 4. 2068 Hz

True or False:

1.False (sound can travel in solids, gases and liquids but can’t travel through vacuum)

2.True

3.False (Velocity of sound is independent of gas pressure but dependent of Temperature)

4.False (Velocity of sound is greater in the liquids and solids than gases – V_s < V_L < V_S)

Match the following:

1. 10Hz 2. Ultrasonography 3. 22kHz 4. Compressions

Reason and Assertions:

1. Both assertion and reason are true and reason is the correct explanation of assertion.
2. Both assertion and reason are true but reason is not the correct explanation of assertion.