Echo

Q.

The speed of sound in air is 344 m/s. In order to hear distinct echoes in air, the distance of the obstacle from the source of sound should be:

1. at most 17.2 m

2. at least 17.2 m

3. equal to 17.2 m

4. depends on the medium

Q.

Why do echoes produced in an empty auditorium usually decrease when it is full of people?

Q. What minimum distance is required between the source of sound and the reflecting surface to hear the echo? Give reason.

Q. Some animals get disturbed and start running here and there just before the earthquakes occur because they can hear:

1. Audible sound
2. Ultrasonic sound
3. None of the above
4. Infrasonic sound

Q.

A man standing in front of a vertical cliff fire a gun. He hears the echo after $3\mathrm{s}$. On moving closer to the cliff by $82.5\mathrm{m}$, he fires again. This time, he hears the echo after $2.5\mathrm{s}$. Calculate the distance of the cliff from the initial position of the man.

Q.

The sound heard after reflection is___________.

Q. Fill in the blanks​ ​

• The sound heard after reflection is

Q.

Name two reflectors of sound.

Q.

Ram is standing $165m$ behind Shyam. Shyam is standing '$d$' meters away from a wall in the same line. 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 $330m{s}^{-1}$)

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

Q.

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

Q.

A man standing in front of a vertical cliff fire a gun. He hears the echo after $3\mathrm{s}$. On moving closer to the cliff by $82.5\mathrm{m}$, he fires again. This time, he hears the echo after $2.5\mathrm{s}$. Calculate the velocity of sound.

Q. A person claps his hands in an empty room. He hears the echo of the sound after 5 seconds. What is the distance between the person and the wall of the room?
(Take the speed of sound in air = 340 m <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> $s^{-1}$)

1. 
   912 m
2. 
   3500 m
3. 
   850 m
4. 
   999 m

Q. The technique used by bats for navigation and location of food is:

1. Echolocation
2. Reflection of light
3. Echocardiography
4. Ultrasonography

Q.

A man standing in front of a vertical cliff fires a gun and hears the echo after $4$ seconds. He moves $150m$ towards the cliff and again fires the gun. This time, he hears the echo after $3.6$ seconds. Find the distance of the cliff from his first position.

1. $7500m$

2. $550m$

3. $750m$

4. $1500m$

Q. If a child hears an echo from a cliff 6 second after the sound produced by shouting, how far is the cliff?

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

Q.

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

1. Because time gap between direct sound and reflected sound is too low to be perceptible by human ear

2. Because small rooms reflect less amount of energy

3. Because small rooms absorb more sound

4. Because of multiple reflections in small rooms

Q. To hear an echo, time interval between the original sound and the echo is ___.

1. 0.05 s
2. less than 0.1 s
3. less than 0.05 s
4. more than 0.1 s

Q. Three boys rahul, raju, and ravi stand at three places and clap their hands simultaneously. Calculate the time between the clap and the echo of the clap of each body. Infer how can the time between the clap and echo of the clap varied. Velocity of sound in air is ${330ms}^{-1}$.

Q.

Statement 1: Ram is standing at a distance of 33 m from a wall. He claps and hears the echo of his own clap.
Statement 2: Velocity of sound in air is 330 m/s and time of persistence for hearing is $\frac{1}{10}$ of a second.

1. Statement 1 is false but information in statement 2 is insufficient to prove it

2. Statement 1 is false and information in statement 2 is sufficient to prove it

3. Statement 1 is true and information in statement 2 is sufficient to prove it

4. Statement 1 is true but information in statement 2 is insufficient to prove it

Q. A boy stands between the two walls as shown below and he claps his hands.


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 $344m{s}^{-1}$.

1. $36m$
2. $34m$
3. $17m$
4. $40m$

Q.

What is an echo?

1. Reflection of sound reaching to the listener some time before direct sound

2. Reflection of sound reaching to the listener some time after direct sound

3. Reflection of sound reaching to the listener with direct sound

4. Depends on position of listener

Q.

Why does sound echo in an empty room, but not so in a living room/??