Tag: physics

Questions Related to physics

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

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

  1. no sound will be heard

  2. no echo will be heard

  3. echo can be heard

  4. none

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Correct Option: B
Explanation:

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

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

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

  1. quite small, rigid

  2. quite small, soft

  3. quite large, rigid

  4. quite large, soft

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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.

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:

physics acoustics 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. cant be predicted

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 $25^o$C is more than 17.2 m.
The speed of sound increases with rise in temperature.

Echo can be heard if 

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

  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

Show answer
Correct Option: C
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.

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. all

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.

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

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 17.2 m. This condition is followed here but for the production of an echo, the obstacle should be rigid.

Fill in the following blanks with suitable words
(a) An echo is simply a ______ sound.
(b) Pitch of sound depends on __.
(c) Loudness of sound depends on _.
(d) Quality of sound depends on_.
(e) Echoes are caused by the ______ of sound.

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

  1. (a) Reflected, (b) Frequency, (c) Amplitude, (d) Waveform, (e) Reflection

  2. (a) reflection, (b) amplitude, (c) frequency, (d) waveform, (e) reflected

  3. (a) waveform, (b) reflected, (c) reflection, (d) frequency, (e) amplitude

  4. (a) frequency, (b) waveform, (c) reflected, (d) amplitude, (e) reflection

Show answer
Correct Option: A
Explanation:

$1.$ Echo is simply the reflection of sound that arrives at the listener with a delay after the direct sound.

$2.$ Pitch is the quality of sound governed by the rate of vibrations producing it. It depends on the frequency of the sound.
$3.$ Loudness is the subjective perception of sound pressure.  It depends on the amplitude.
$4.$ Quality of sound depends on the waveform. By analyzing the shape of the wave we can determine the quality of sound.
$5.$ Echoes are caused by the reflection of sounds that arrives at the listener with a delay after the direct sound.

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

Show answer
Correct Option: B
Explanation:

Rooms having walls less than 17.2 m away from each other, no echo can be heard. here, 159 m is greater than 17.2 m. So an echo will be heard if other conditions are fulfilled.

When echo is heard?

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

  1. If the time interval between original sound and reflected sound is more than 1/10s.

  2. If the time interval between original sound and reflected sound is less 1/10s.

  3. If the time interval between original sound and reflected sound is less than 1/120s.

  4. If the time interval between original sound and reflected sound is 1/120s

Show answer
Correct Option: A
Explanation:

If the time interval between original sound and reflected sound is more than $\frac{1}{10}\,s$, then the original sound and the reflected sound can be clearly heard. This reflected sound is known as echo.

An echo is heard on a day when temperature is about $44^0$C. When will the echo be heard if the temperature falls to $80^0$C?

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

  1. Sooner

  2. Later

  3. At the same time

  4. No echo will be heard

Show answer
Correct Option: A
Explanation:

Time, after which an echo is heard is given by $t = \dfrac {Distance}{Speed \ \ of \ \ sound \ \ in \ \ air}$
Therefore, since speed of sound in air increases with the increase in temperature, so the time after which echo will be heard decreases. Hence, echo will be heard, sooner than the echo heard when temperature near $44^0C$