Tag: conditions for hearing echo

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Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

An echo of the sound produced can be heard only if it reaches our ear after -

  1. 1 / 15th of a second

  2. 1 / 13th of a second

  3. 1 / 10th of a second

  4. 1 / 5th of a second
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An echo is the repetition of sound that results as a reflection from a surface. An echo of the sound produced can be heard only if it reaches our ear after 1 / 10th of a second. This is due to the persistence of sound.

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

In order to produce an echo, the minimum distance between the source of the sound and the reflecting body should be :

  1. 14 m

  2. 16 m

  3. 17 m

  4. 20 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of sound to be 344 m/s at a given temperature, say at 22 $^0C$ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s.
 
Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344 m/s) ×0.1 s = 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance. I.e., $\frac{34.4}{2} \approx 17 \,m$

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

The minimum distance between the source of a sound and reflecting body should be 17 m for the formation of an echo. True or false

[consider the medium to be air]

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of sound to be 344 m/s at a given temperature, say at 22 $^0C$ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s.
 
Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least (344 m/s) ×0.1 s = 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance. I.e., $\frac{34.4}{2} \approx 17 \,m$

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

The time gap between the two sounds-direct and echo depends upon:

  1. medium through which the sound travels

  2. the type of obstacle

  3. the speed of sound

  4. All
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The time gap between the two sounds-direct and echo depends upon the medium through which the sound travels. These two sounds can be heard distinctly provided the Distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him without interfering with the direct sound.

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

The direct sound and the echo can be heard differently provided:

  1. Distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him interfering with the direct sound.

  2. Distance between the obstacle and the source is small enough to allow the reflected sound to reach him interfering with the direct sound.

  3. Distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him without interfering with the direct sound.

  4. Distance between the obstacle and the reflecting surface is large enough to allow the reflected sound to reach him interfering with the direct sound.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The time gap between the two sounds-direct and echo depends upon the medium through which the sound travels. These two sounds can be heard distinctly provided the Distance between the observer and the reflecting surface is large enough to allow the reflected sound to reach him without interfering with the direct sound.

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

For the production of an echo, size and nature of obstacle should be:

  1. quite small, rigid

  2. quite small, soft

  3. quite large, rigid

  4. quite large, soft
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For the production of an echo, the reflecting surface or the obstacle should be rigid such as building, hill, cliff.
Echo can be produced if the size of the obstacle reflecting the sound is quite large.

Multiple choice physics acoustics conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

The minimum distance in air between the observer and the obstacle for an echo to be heard clearly at temperatures higher than $25^o$C is:

  1. less than 17.2m

  2. more than 17.2m

  3. equal to 17.2m

  4. cant be predicted
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The minimum distance in air between the observer and the obstacle for an echo to be heard clearly at temperatures higher than $25^o$C is more than 17.2 m.
The speed of sound increases with rise in temperature.

Multiple choice physics study of sound conditions for hearing echo echo reflection of sound and echo ultrasound and its applications

Echo can be heard if 

  1. the minimum distance between the source of sound and the obstacle is $17m$

  2. the obstacle is rigid and hard.

  3. both A and B hold

  4. none of A and B hold
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The options are the conditions for an echo to be produced. The obstacle should be rigid at a minimum distance of $17m$ for an echo to be produced.