Q: A ship sends an ultrasound pulse to the sea bed and receives the echo after 2 s. If the speed of sound in water is 1500 m/s, the depth of the sea is:

1500 m. Total path = 1500 \times 2 = 3000 m; depth = \dfrac{3000}{2} = 1500 m (this method is SONAR).

Question 1

An echo is heard because sound is:

Accepted Answer

reflected back from a distant obstacle. An echo is the repetition of a sound caused by its reflection from a surface.

Question 2

A person shouts towards a cliff and hears the echo after 3 s. If the speed of sound is 340 m/s, the distance of the cliff is:

Accepted Answer

510 m. Sound travels to the cliff and back: total distance = 340 	imes 3 = 1020 m, so the cliff is \dfrac{1020}{2} = 510 m away.

Question 3

To hear a distinct echo, the reflecting surface must be at least about 17 m away because:

Accepted Answer

the ear can distinguish two sounds separated by at least 0.1 s. The ear resolves sounds ~0.1 s apart; in 0.1 s sound travels 34 m (there and back), so the surface must be at least ~17 m away.

Question 4

The persistence of sound in a large hall due to repeated reflections is called:

Accepted Answer

reverberation. Reverberation is the prolonging of sound by multiple reflections before it dies out.

Question 5

The ceilings and walls of cinema halls are made of sound-absorbing materials to:

Accepted Answer

reduce reverberation. Absorbing materials cut down repeated reflections, reducing reverberation so speech is clear.

Question 6

A ship sends an ultrasound pulse to the sea bed and receives the echo after 2 s. If the speed of sound in water is 1500 m/s, the depth of the sea is:

Accepted Answer

1500 m. Total path = 1500 	imes 2 = 3000 m; depth = \dfrac{3000}{2} = 1500 m (this method is SONAR).

Echo & Reverberation — Homi Bhabha Exam Physics MCQs with Solutions

Questions with solutions