Tag: ultrasound and its applications

Questions Related to ultrasound and its applications

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

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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

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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

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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. $70\ m$

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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

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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

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Correct Option: B
Explanation:

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

A signal source starts from rest and moves away from a stationary wall with an acceleration of $0.5 m/s^2$. After what time in secs will we hear an echo

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

  1. $1.2 $

  2. $8.2 $

  3. $18.2 $

  4. $4.2 $

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Correct Option: B
Explanation:

Distance required for an echo to be heard is 17 m. Thus, $17 =  0 + \dfrac{0.5 t^2}{2} \implies t= 2\sqrt{17}=8.2 s$. 

The correct option is (b)

A source of sound is kept at a distance of 10 m from a wall. What distance should it be moved further, so that an echo is heard

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

  1. 10 m away from the wall

  2. 7 m away from the wall

  3. 7 m towards the wall

  4. 10 m towards the wall

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Correct Option: B
Explanation:

To hear an echo, the distance between the source and the reflector should be atleast 17 m. Thus the source should be moved 7 m away from the wall

The correct option is (b)

A source of sound moves with an uniform velocity away from a wall. An echo is heard at 4th second from its beginning position, what is the speed of the source

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

  1. 10 m/s

  2. 7 m/s

  3. 4.25 m/s

  4. 1 m/s

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Correct Option: C
Explanation:

distance moved by the source = 17 m for the echo to be heard

Thus, $17 = v(4) \implies v = 17/4 = 4.25 $ m/s

The correct option is (c)