Tag: study of sound

Quizzes (14) Questions (314)

Questions Related to study of sound

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 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.

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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)

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 sound and the reflecting surface, in order to hear an echo, must be

  1. $0.65\space m$
  2. $1.65\space m$
  3. $16.5\space m$
  4. $165\space m$
Reveal answer Fill a bubble to check yourself
C Correct answer
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  $d = v  t$
$2  x = 330  \times 0.1             \implies x = 16.5   m$

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

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

  1. 60 m

  2. 25 m

  3. 30 m

  4. 17 m
Reveal answer Fill a bubble to check yourself
C Correct answer
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  $d = v  t$
$2  x = 600  \times 0.1             \implies x = 30   m$

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

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 

  1. 17.11 m

  2. 117.2 m

  3. 173 m

  4. 865 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The total distance traveled by the sound is speed times time: 346 m/s * 5 s = 1730 m. Since the sound travels to the cliff and back, the distance to the cliff is half of the total distance: 1730 / 2 = 865 m.

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

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 $335\ ms^{-1})$.

  1. $167.5\ Hz$
  2. $152.5\ Hz$
  3. $175\ Hz$
  4. $145\ Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The engine is moving toward the hill at 15 m/s (54 km/h). The frequency of the echo is f' = f * (v + vs) / (v - vs), where v is speed of sound and vs is speed of engine. f' = 160 * (335 + 15) / (335 - 15) = 160 * 350 / 320 = 175 Hz.

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

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 $=340m/s$)

  1. $72m/s$
  2. $31m/s$
  3. $31mph$
  4. $60kmph$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Distance = 1020 m. Total sound distance = 2 × 1020 = 2040 m. If echo is heard after 1.5 s (assuming 11/2 means 1.5), time available for driver approach = (2040/340) - 1.5 = 6 - 1.5 = 4.5 s. Speed = 1020 / 4.5 = 31 m/s (approximately).

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

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 $= 1400\; ms^{-1}$)

  1. 60

  2. 140

  3. 90

  4. 70
Reveal answer Fill a bubble to check yourself
D Correct answer
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.