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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 the obstacle should be :

  1. small and rigid respectively

  2. small and soft respectively

  3. large and rigid respectively

  4. large and soft respectively
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

In a room two walls are at a distance of 159 m. Then :

  1. no echo will be heard

  2. an echo can be heard

  3. no sound will be heard

  4. none of these are true
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In rooms having walls less than 17.2m away from each other, no echo can be heard. Here,walls of the room are at a distance of 159 m, much greater than 17.2m. So an echo will be heard if other conditions are fulfilled.

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

A sponge is kept at a distance of 19m from a source of sound.

  1. No echo will be heard

  2. An echo can be heard

  3. No sound will be heard

  4. None of the above is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The minimum distance in air between the observer and the obstacle for an echo to be heard clearly is nearly 17.2m. This condition is followed here but for the production of an echo, the obstacle should be rigid.

Multiple choice physics study of sound 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 ${25}^{0}C$ is :

  1. less than $17.2m$
  2. more than $17.2m$
  3. equal to $17.2m$

  4. unpredictable
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 ${25}^{0}C$ is more than $17.2m$. 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

The minimum distance between the source of sound and the reflecting surface necessary to cause echo is

  1. $1.7\ m$
  2. $17\ m$
  3. $7\ m$
  4. $70\ m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The human ear can hear two sounds distinctly only if there is a time interval of $\frac{1}{10}$seconds between them. Now, the speed of sound in air at $20^0$C is $340m/s$, so the distance traveled in $\frac{1}{10}$seconds will be: 
Distance = Speed X time 
$=340 \times \frac{1}{10} \= 34m$

Thus, it is possible to hear the echo at the minimum distance of $\frac{34}{2}= 17m$ between the source of sound and reflecting surface. 

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

The minimum distance to hear a clear echo is (V is the velocity of sound)

  1. 2V/5

  2. 5V/2

  3. V/20

  4. 5V
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Minimum frequency to the human ear is 20
$\therefore T= \dfrac {1} {F}$
$T=\dfrac{1} {20}$
$d= V \times t$
$d= V\times \dfrac {1} {20}$
$\therefore$ The minimum distance is$ \dfrac {V} {20}$, where V is speed of the sound.

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

A man, standing between two cliffs, claps his hands and starts hearing a series of echoes at intervals of one second. If the speed of sound in air is $340ms^{-1}$, the distance between the cliffs is?

  1. $680$m
  2. $1700$m
  3. $340$m
  4. $1620$m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the distance between the two cliffs be d. Since, the man is standing midway between the two cliffs, then the distance of man from either end is $d/2$.
The distance travelled by sound (in producing an echo)
$2\times \displaystyle\frac{d}{2}=v\times t\Rightarrow d=340\times 1=340$m.