Tag: study of sound

Questions Related to study of sound

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. 

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.

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

Show answer
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)

To hear an echo, the minimum distance between source of sound and reflecting body is 17m.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

to hear echo of a sound the minimum distance between source and reflecting surface should be 17m.

so the answer is A.

The minimum distance between the sound and the reflecting surface, in order to hear an echo, must be

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

  1. $0.65\space m$

  2. $1.65\space m$

  3. $16.5\space m$

  4. $165\space m$

Show answer
Correct Option: C
Explanation:

Let the distance between the source of sound and the obstacle be $x$ metres .

Thus the distance travelled by sound to reach back to the source   $d = 2  x$
As the minimum time required to hear an echo is equal to $ 0.1  sec$
As velocity of sound in air    $ v = 330   m/s$
Thus  $d = v  t$
$2  x = 330  \times 0.1             \implies x = 16.5   m$

Velocity of sound in the atmosphere of a planet is 600m$s^{-1}$. The minimum distance between the source of sound and the obstacle to hear echo should be

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

  1. 60 m

  2. 25 m

  3. 30 m

  4. 17 m

Show answer
Correct Option: C
Explanation:

Let the distance between the source of sound and the obstacle be $x$ metres .

Thus the distance travelled by sound to reach back to the source   $d = 2  x$
As the minimum time required to hear an echo is equal to $ 0.1  sec$
Thus  $d = v  t$
$2  x = 600  \times 0.1             \implies x = 30   m$

A person clapped his hands hear cliff and heard a echo after 5s. The minimum distance of the cliff from the person if the speed of sound is take as 346 m/s 

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

  1. 17.11 m

  2. 117.2 m

  3. 173 m

  4. 865 m

Show answer
Correct Option: D

A rail engine approaches a hill at a speed of $54\ kmph$ whistling a sound of frequency $160\ Hz$. The frequency of echo heard by the engine driver is (velocity of sound in air $335\ ms^{-1})$.

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

  1. $167.5\ Hz$

  2. $152.5\ Hz$

  3. $175\ Hz$

  4. $145\ Hz$

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Correct Option: C

A driver blows the horn when he is at a distance of $1020m$ from a stiff. He hears the echo after $11/2sec$. At what rate is he approaching the cliff. (velocity of sound in air $=340m/s$)

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

  1. $72m/s$

  2. $31m/s$

  3. $31mph$

  4. $60kmph$

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Correct Option: B

What should be the minimum distance (in m) between source and reflector in water so that echo is heard distinctly ? (The speed of sound in water $= 1400\; ms^{-1}$)

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

  1. 60

  2. 140

  3. 90

  4. 70

Show answer
Correct Option: D
Explanation:

The sensation of any sound persists in our ear for about 0.1 seconds. This is known as the persistence of hearing. If the echo is heard within this time interval, the original sound and its echo cannot be distinguished. So the most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound dies off. 
As the speed of sound in water is 1400 m/s in the question, the distance traveled by sound in 0.1 second is 35 m, which is calculated from the formula 
$Distance\; traveled=velocity\; of\; sound \times time\; taken$. That is, 140 m. This is twice the minimum distance between a source of sound and the reflector. So, if the obstacle is at a distance of 70 m at least, the reflected sound or the echo is heard after 0.1 second, distinctly.