Physics · Science General

Acoustics and Sound Waves

2,160 Questions

Acoustics and sound waves deal with mechanical vibrations traveling through media like air and water. Key concepts include wave reflection, beats, echoes, the Mach number, and infrasound. These physics fundamentals are regularly tested in general science sections of multiple competitive exams.

Sound wave propagationEchoes and reflectionWave interferenceMach numberInfrasound frequency

Acoustics and Sound Waves Questions

Multiple choice physics beats in sound waves

When a long hollow cylindrical iron pipe is struck at one end, then at the other end of the pipe :

  1. one sound is only heard

  2. two sounds are heard at different intervals

  3. three sounds are heard at different intervals

  4. no sound is heard
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

There will be two sounds, one will through the air , and other will come through the material, Sound speed is faster in steel, therefore it will be heard earlier than the sound from air . Option "B" is correct.

Multiple choice physics beats in sound waves

A source of sound of frequency 256 Hz is moving towards a wall with a velocity of 5 m/s. The number of beats per second heard by a stationary observer between the source and the wall is (Velocity of sound = 330 m/s) 

  1. 8

  2. 3

  3. 5

  4. 2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
 If the sound reaches the observer after being reflected from a stationary surface and the medium is also stationary$,$ 
the image of the source in the reflecting surface will become the source of the reflected sound$.$
$v = v [c – v-o/c – v _s]$
$v _o,$ $v _s$ are $+ve$ if they are directed from source to the observer and $– ve$ if they directed from observer to source$.$
$v = 256 [330 – (- 5)/330 – 5] = 264 Hz$
$∴$ Beat frequency $= 264 – 256 = 8$
Hence,
option $(A)$ is correct answer.
Multiple choice physics beats in sound waves

Megaphones or loudhailers, horns, musical instruments such as trumpets and shehanais, are all designed to---------

  1. send sound in a particular direction without spreading it in all directions

  2. send sound in a particular direction spreading it in all directions

  3. collect sound from all directions spreading it in all directions

  4. all
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Megaphones or loudhailers, horns, musical instruments such as trumpets and  shehanais, are all designed to send sound in a particular direction without spreading it in all direction. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.

Multiple choice physics beats in sound waves

The lowest wavelength of audible sound is (Velocity of sound in air is $340ms^{-1}$)

  1. $1.7cm$
  2. $17m$
  3. $20cm$
  4. $20000m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice physics beats in sound waves

The maximum time period for a sound wave that the audible to normal human being is

  1. $0.5s$
  2. $5s$
  3. $0.05s$
  4. $0.005s$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The maximum time period corresponds to the minimum frequency. For a human, the minimum frequency is 20 Hz. T = 1/f = 1/20 = 0.05 seconds.

Multiple choice physics beats in sound waves

The musical interval between tube two tine of frequency $400\ Hz$ and $200\ Hz$ is:

  1. $2$
  2. $200$
  3. $1$
  4. $none\ of\ these$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The musical interval is defined as the ratio of the two frequencies: 400 Hz / 200 Hz = 2.

Multiple choice physics beats in sound waves

A key of mechanical piano is first struck gently and then struck again but much harder this time. In the second case :

  1. sound will be louder but pitch will not be different

  2. sound will be louder and the pitch will also be higher

  3. sound will be louder but pitch will be lower

  4. both loudness and pitch will remain unaffected
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Loudness or softness of a sound is determined basically by its amplitude. The amplitude of the sound wave depends upon the force with which an object is made to vibrate. If we strike a table lightly, we hear a soft sound because we produce a sound wave of less energy (amplitude). Pitch depends upon frequency received by the human ear.

Multiple choice physics beats in sound waves

The characteristics of sound with the help of which we can distinguish between a SHRILL note and a GRAVE note is

  1. Loudness

  2. Pitch

  3. Quality

  4. Intensity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pitch is the characteristic of sound that allows us to distinguish between a shrill note (high frequency) and a grave note (low frequency).

Multiple choice physics beats in sound waves

How Jal Tarang produces sound?

  1. In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency.

  2. In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest pitch.

  3. In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency. As the amount of water in the cup goes on increasing, the frequency of the sound produced also goes on increasing.

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

n Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency or lowest pitch. As the amount of water in the cup goes on increasing, the frequency (or the pitch) of the sound
produced also goes on increasing.

Multiple choice physics beats in sound waves

Beats are heard at the rate of $12$ every $5$ seconds when two open organ pipes of lengths $84\ cm$ and $85\ cm$ are sounded together in their fundamental modes. Find the velocity of sound in air. (An open organ pipe has an antinode at each end.

  1. $342.7\ m/s$.
  2. $300.7\ m/s$.
  3. $350.7\ m/s$.
  4. $400.7\ m/s$.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For an open organ pipe, fundamental frequency f = v / 2L. f1 = v / (2 * 0.84), f2 = v / (2 * 0.85). Beat frequency |f1 - f2| = (v/2) * (1/0.84 - 1/0.85) = 12/5 = 2.4. (v/2) * (0.01 / (0.84 * 0.85)) = 2.4. v = 2.4 * 2 * 0.84 * 0.85 / 0.01 = 342.72 m/s.

Multiple choice physics beats in sound waves

An under water swimmer sends a sound signal to the surface. It is produces 5 betas/sec when compared with fundamental tone of a pipe of $20$ cm length closed at one end what is wavelength of sound in water. (take V water=$1500 m/sec$ Vair=$360 m/sec$)

  1. $3.3 m$ or $3.37 m$
  2. $4.4 m$ or $4.47 m $
  3. $2.5 m$ or $2.7 m$
  4. $1 m$ or $1.7 m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A pipe of length 0.2 m closed at one end has fundamental frequency f = v_air / (4L) = 360 / (4 * 0.2) = 450 Hz. The swimmer's signal frequency f_s satisfies |f_s - 450| = 5, so f_s = 455 or 445 Hz. Wavelength in water lambda = v_water / f_s = 1500 / 455 = 3.296 m or 1500 / 445 = 3.37 m.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

Three different vibrating bodies produce three types of sounds X, Y and Z. Sounds X and Y cannot be heared by a man having normal range of hearing but sound Z can be heard easily. The sound X is used in for monitoring nuclear reactor.The sound similar to that which is produced during an earthquake before the main shock wave is generated. What type of sounds are (i) X (ii) Y, and (iii) Z?

  1. X-infrasound

    Y-ultrasound

    Z- audible sound

  2. X-audible sound

    Y-infrasound

    Z-ultrasound

  3. X-ultrasound

    Y-infrasound

    Z-audible sound

  4. X-infrasound

    Y-audible sound

    Z-audible sound
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ultrasound is used to see what is happening in a nuclear reactor.Ultrasounds and infra sounds are not audible to man.ultrasound have frequency more than
20kHz. Infrasound have frequency below 20Hz