Echo

Q. What is echo?

Q. Question 1
An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is $342m{s}^{-1}$?

Q.

What is meant by an echo?

Q.

What is the reflection of sound waves?

Q.

(a) What is an echo? How is echo formed?

(b) What is the minimum distance in air required from a sound reflecting surface to hear an echo (at ${20}^o$ C)?

(c) A man standing 825 metres away from a cliff (steep rock) fires a gun. After how long will he hear its echo? The speed of sound in air is $330m/s$.

Q.

What type of surface is needed for the reflection of sound waves?

A- Smooth surface only

B- Smooth and polished surfaces

C-Hard surfaces only

D-Polished and rough surface

Q. Why echoes can't be heard clearly in a small room?

1. Because small rooms absorb more sound.
2. Beacuse time gap between direct sound and reflected sound too low to be perceptible by human ear.
3. Because small rooms reflect less amount of energy.
4. Because the minimum distance required to hear an echo in a small room is less than 17.2 m

Q. Question 1
Why are the ceilings of concert halls curved?

Q.

Reflection of sound is called:

1. Tone quality

2. Pitch

3. Loudness

4. Echo

Q.

What does echolocation mean?

Q.

What name is given to the repetition of sound caused by the reflection of sound waves ?

Q.

The echo of a sound is heard after 5 seconds. If the speed of sound in the air is 342 m/s. calculate the distance of the reflecting surface.

Q.

Explain how echo is produced?

Q.

Which property of sound leads of the formation of echoes ?

Q.

The speed of sound in water is 1500 metres per second. How far away from an under-sea rock should a deep sea diver be so that he can hear his own echo ?

Q.

On which day, a hot or a cold day, an echo is heard sooner ? Give reason for your answer.

Q.

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sounds on a hotter day?

Q.

A person shouts near a wall and heard the echo after 10 sec. What is the distance of the wall from the person? (take speed of sound=$346m{s}^{-1}$)
[2 MARKS]

Q.

At a prayer meeting, the disciples sing JAI-RAM JAI-RAM. The sound amplified by a loudspeaker comes back after reflection from a building at a distance of$80m$ from the meeting. What maximum time interval can be kept between one JAI-RAM and the next JAI-RAM so that the echo does not disturb a listener sitting in the meeting. The speed of sound in air is $320m{s}^{-1}$.

Q. A man fires a gun and hears the echo from the cliff after 2 seconds. He walks towards cliff about a distance of 85 m and fires the gun again. He hears echo after 1.5 seconds. In this case, the velocity of sound in air is

1. 85 m/s
2. 170 m/s
3. 340 m/s
4. 680 m/s

Q.

The speed of sound in air is 330 m/s and the human brain can only distinguish sounds 0.1 s apart. A person is standing beside a source of the sound. What should be the minimum distance between the source and the reflecting surface for the echo to be heard by him?

1. 33 m

2. 16.5m

3. 34m

4. 15m

Q.

What is an echo?

1. Reflection of sound reaching to the listener some time after the original sound

2. Reflection of sound reaching to the listener before original sound

3. Reflection of sound reaching to the listener along with original sound

4. Reflection of sound not reaching to the listener

Q.

An echo is produced due to __________ of sound.

Q.

In which medium, air or water, an echo is heard much sooner? Why ?

Q.

A bat in search of prey hears the echo of its squeak after 0.1 s .How far is the prey from the bat if the squeak got reflected from it?

Q. An echo is heard when the time interval betweeen the original sound and reflected sound is _____.

1. more than $\frac{1}{10}s$.
2. more than $\frac{1}{150}$ s.
3. less than $\frac{1}{150}s$.
4. less than $\frac{1}{10}s$.

Q.

Which phenomenon is used by bats and porpoises?

Q.

A child watching Dussehra celebrations from a distance sees the effigy of Ravana burst into flames and hears the explosion associated with it 2s after that. How far was he from the effigy if the speed of sound in the air that night was 335 m/s?

Q. Question 20
A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.

Q. A person clapped his hands near a cliff and heard the echo. The minimum distance of the cliff from the person if the speed of sound is taken as 346 m/s is

1. 17.1 m
2. 17.2 m
3. 17.3 m
4. 34.6 m