Echo

Q.

The minimum distance between the source and the reflector in air, to hear an echo, is approximately :

(a) 10 m (b) 17 m

(c) 34 m (d) 50 m.

Q.

What is meant by an echo ? State two conditions necessary for an echo to be heard distinctly.

Q.

Why cannot we hear an echo in a small room?

Q. What should be the minimum time interval between the original sound and the reflected sound to hear a distinct echo?

1. 0.1 seconds
2. 0.2 seconds
3. 0.3 seconds
4. 0.4 seconds

Q.

A boy standing in front of a wall at a distance of 85 m produces 2 claps per second. He noticed that the sound of his clapping coincided with the echo. The echo is heard only once when clapping is stopped. Calculate the speed of sound.

Q.

Explain how the speed of sound can be determined by the method of an echo.

Q.

What should be the minimum distance between the source and reflector in water so that the echo is heard distinctly? (The speed of sound in water = 1400 m $s^{-1}$).

Q.

A pendulum has a frequency of 5 vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears the echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 m $s^{-1}$, find the distance between the cliff and the observer.

Q.

Sound waves cannot travel in a vacuum. It can travel only through a material medium. e.g., solids, liquids and gases. An echo is heard after 0.8 s when a person fires a cracker 130 m from a high building:

(ii) Why sound cannot travel through a vacuum?

Q.

Calculate the minimum distance in air required between the source of sound and the obstacle to hear an echo. Take speed of sound in air = 350 m $s^{-1}$.

Q. An observer stands at a distance of $850m$ from the cliff and fires a gun. After what time gap will he hear the echo, if sound travels at a speed of $350m{s}^{-1}$ in air?

1. $4.00s$

2. $6.89s$

3. $2.93s$

4. $4.86s$

Q.

A man standing 25 m away from a wall produces a sound and receives the reflected sound.

(a) Calculate the time after which he receives the reflected sound if the speed of sound in air is 350 m $s^{-1}$.

(b) Will the man be able to hear a distinct echo? Explain the answer.

Q.

An echo is simply a reflected sound.

1. True
2. False

Q. (i) What is an echo?
(ii) State two conditions for an echo to take place.

Q.

(i) Name the type of wave which are used for sound ranging.
(ii) Why are these waves mentioned in $\left(i\right)$ above, not audible to us?

Q.

A ship on the surface of water sends a signal and receives it back from a submarine inside water after 4 s. Calculate the distance of the submarine from the ship. (The speed of sound in water is 1450 m $s^{-1}$).

Q. A man standing in front of a vertical cliff fires a gun and hears the echo after 4 seconds. He moves 175 m towards the cliff and fires the gun again. This time, he hears the echo after 3 seconds. Find the correct statement(s).

Note: Question can have mutliple correct options

[2 marks]

1. The distance between the initial position of the man and the cliff is 700 m.
2. Speed of sound is 350 m/s.
3. Speed of sound is 320 m/s.
4. The distance between the initial position of the man and the cliff is 350 m.

Q.

A man is standing at a distance of 12 m from a cliff. Will be he able to hear a clear echo of his sound ? Give a reason for your answer.

Q.

What are the conditions for echo generation? why do we not hear a sound echo in our bedroom?

Q.

A man fires a gun and hears its echo after 5 s.The man moves 310 m towards the hill and fires his gun again.This time if he hears the echo after 3 s, calculate the speed of sound.

Q.

Name the waves used for echo depth sounding?

Q.

A man stands at a distance of 68 m from a cliff and fires a gun.
The time interval after which will he hears the echo is:

[Take the speed of sound in air is 340 m s-1]

1. 0.1 s

2. 6.8 s

3. 2.0 s

4. 0.4 s

Q.

Lightning can be seen as the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = $330\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$).

Q.

John fires a gun towards a hill and hears its echo after 5 seconds. He then moves 320 m towards the hill and fires his gun again. This time he hears the echo after 3 seconds. Calculate i) the velocity of sound and ii) distance between the original position of man & the hill.

1. i) 340 ms^-1 and ii) 824 m

2. i) 320 ms^-1 and ii) 800 m

3. i) 320 ms^-1 and ii) 824 m

4. i) 340 ms^-1 and ii) 800 m

5. i) 330 ms^-1 and ii) 850 m

Q.

If a child hears an echo from a cliff $6$ seconds after the sound produced by shouting, how far is the cliff? (speed of sound = $340m/s$)

1. 58 m
2. 1032 m
3. 68 m
4. 1000 m

Q.

A man standing between two parallel cliffs, fires a gun and hears two successive echoes after 4 and 6 seconds. Calculate the distance between the cliffs. (Vel. of sound in air is 330 ms⁻¹)

1. 165 m

2. 1650 cm

3. 165 cm

4. 1650 m

Q. Echo is due to:

1. Reflection of sound
2. Dispersion of sound
3. Refraction of sound
4. None of the above

Q.

A boy stands between the two walls and claps his hands as shown below:

If $x$ is less than $60m$ and the time between the first and the second echo is $0.25s$, then calculate the distance $x$. (Velocity of sound in air is 344 $m{s}^{-1}$)

1. 36m

2. 34m

3. 40m

4. 17m

Q.

We hear the sound of thunder after the flash of lightning is seen. Give reason.

Q. Shyam is standing between Ram and a wall on the same line. Distance between Ram and Shyam is $165m$. Shyam is standing $d$ meters away from the wall. Ram claps and Shyam hears the clap two times at an interval of $2$ seconds. Find the value of $d$.

(Assume velocity of sound to be $330m/s$)

1. 660 m
2. 330 m
3. 82.5 m
4. 165 m