Tag: physics

Questions Related to physics

A room have two walls at a distance of 12m :

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

  1. no sound will be heard in the room

  2. no echo will be heard in the room

  3. echo can be heard in the room

  4. none of the above are true

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Correct Option: B
Explanation:

In rooms having walls less than 17.2m away from each other, no echo can be heard.

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

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

  1. small and rigid respectively

  2. small and soft respectively

  3. large and rigid respectively

  4. large and soft respectively

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Correct Option: C
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.

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

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

  1. no echo will be heard

  2. an echo can be heard

  3. no sound will be heard

  4. none of these are true

Show answer
Correct Option: B
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.

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

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

  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

Show answer
Correct Option: A
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.

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 :

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

  1. less than $17.2m$

  2. more than $17.2m$

  3. equal to $17.2m$

  4. unpredictable

Show answer
Correct Option: B
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.

For the production of an echo, the reflecting surface should be :

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

  1. rigid

  2. soft

  3. very near

  4. none of these

Show answer
Correct Option: A
Explanation:

For the production of an echo, the reflecting surface or the obstacle should be rigid such as building, hill, cliff etc.

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

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

  1. $1.7\ m$

  2. $17\ m$

  3. $7\ m$

  4. $70\ m$

Show answer
Correct Option: B
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. 

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

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

  1. 2V/5

  2. 5V/2

  3. V/20

  4. 5V

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Correct Option: C
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.

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?

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

  1. $680$m

  2. $1700$m

  3. $340$m

  4. $1620$m

Show answer
Correct Option: C
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.

If two consecutive signals with a difference of 0.1 s are incident on a rock, distant 20 m from the source, will we get two echoes

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

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

The echo of the first signal will overlap with the second signal. Thus, an echo will not be absent