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3. An underwater SONAR source operating at a frequency of 60 kHz directs its beam

towards the surface. If the velocity of the sound produced by it is 330 m/s,
wavelength and frequency of the waves in air are

a) 5.5 mm, 60 kHz.
b) 330 m, 60 kHz.

c) 5.5 m, 60 kHz.

d) 5.5 m, 30 kHz.

4. A wave length 0.60 cm is produced in air and it travels at a speed of 300 ms . It
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will be

a. Audible wave.

b. Infrasonic wave.

c. Ultrasonic wave.

d. Electromagnetic wave.

5. To clean small, intricate metal items such as jewellery and small machine parts, we

use

a. Audible sound.

b. Infra sound.

c. Ultra sound.

d. Electromagnetic waves.

SUBJECTIVE

1. Explain how bats use ultrasounds to catch a prey?

2. Explain how moths of certain families are able to escape capture from a bat?

Numericals [Board]

1. A ship sends a pulse of ultrasound and receives an echo 0.2 seconds later. If the
speed of sound in water is 1000 m/s, find the depth of the sea?

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