Physics · Science General

Acoustics and Sound Waves

2,006 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 propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

Correct comparison between light waves and sound waves is:

  1. Both are mechanical waves

  2. Both need a material medium for propagation

  3. Both can travel through vacuum

  4. None
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sound waves are mechanical waves, light waves are electromagnetic waves. Light can travel through vacuum, sound cannot.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

Light and Sound waves

  1. both are mechanical waves

  2. both need material media for propagation

  3. both can travel through vacuum

  4. are two different types of waves
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sound waves are mechanical waves which are longitudinal in nature and require material media to pass through.

Light waves are electromagnetic waves which are transverse in nature and do not require any material medium to pass through.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The thunder of a cloud is heard later compared to flash of lightning because :

  1. speed of sound is greater than speed of light

  2. speed of light is greater than speed of sound

  3. speed of sound is the same as speed of light

  4. sound is obscured by the rain
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The light travels much faster than the sound. The thunder travels at the speed of sound while the light from the flash travels at the speed of the light. The speed of light is about 340 m/s through air, while the speed of light is about 300 million m/s.So the thunder is heard after the flash of lightening.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

A worker lives at a distance of 1.32 km from the factory. If the speed of sound in air is 330 m$s^{-1}$, how long will the sound of factory siren take to reach the worker?

  1. 1 s

  2. 2 s

  3. 3 s

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

Given,


Distance $=1.32\,km=1320\,m$

Speed of sound in air $=330\,m/s$

We have,

$Time=\frac{Distance}{Speed}$

$Time=\frac{1320}{330}=4\,s$

Thus it would take $4\,s$ for the sound of the factory siren to reach the 
worker.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

Two waves of wavelengths $\lambda$ and $(\lambda + \triangle \lambda)$ produce $6$ beats per second. If $\dfrac {\triangle \lambda}{\lambda} = \dfrac {\lambda + \triangle \lambda}{51}$, find the speed of sound wave in a gas in which these waves produce beats?

  1. $316\ m/s$
  2. $310\ m/s$
  3. $306\ m/s$
  4. $326\ m/s$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Beat frequency = 6 Hz. v = f * lambda. Using the relationship between wavelength change and beats, the calculation leads to 326 m/s.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

Flash and thunder are produced simultaneously. But the thunder is heard a few seconds after the flash is seen. Why?

  1. The speed of sound is greater than the speed of light.

  2. The speed of sound is equal to the speed of light.

  3. The speed of light is greater than the speed of sound.

  4. The speed of light is less than the speed of sound.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Flash and thunder are produced simultaneously. But the flash is seen first and then the sound is heard. This is because the speed of sound in air is very less than the speed of light in air.

Speed of sound in air $=334\,m/s$
Speed of light in air $=3\times 10^8\,m/s$

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The time interval between a lightning flash and the first sound of thunder was found to be $5 \ s$. If the speed of sound in air is $330  \ ms^{-1}$, find the distance of flash from the observer.

  1. $1650 \ m$
  2. $165 \ m$
  3. $330 \ m$

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of the sound, distance traveled and the time taken relationship is given as follows.


$Speed\; of\; sound=\dfrac { Distance\; travelled}{ Time\; taken} $

From this equation the Distance traveled is derived as 
$Distance\; travelled=Speed\; of\; sound\times Time\; taken$


That is, $Distance\; travelled=330\; m/s\times 5\; seconds$, given that the speed of sound is 330 m/s.

= 1650 meters.

Hence, the distance of flash from the observer is 1650 meters.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

When a tuning fork of 500 Hz is used, the first and second resonating lengths of closed air column are found to be 18 cm and 54 cm respectively. Find the velocity of sound in S.I. system.

  1. $120{ms}^{-1}$
  2. $240{ms}^{-1}$
  3. $360{ms}^{-1}$
  4. $480{ms}^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For a closed pipe, the resonance lengths are L1 = lambda/4 and L2 = 3*lambda/4. The difference L2 - L1 = lambda/2, so lambda = 2 * (54 - 18) = 72 cm = 0.72 m. Velocity v = f * lambda = 500 * 0.72 = 360 m/s.

Multiple choice physics propagation of sound waves longitudinal vs transverse wave sound and light comparison of speed of sound with speed of light

The frequency of fundamental mode of vibration of an air column enclosed in a closed end pipe is 250 Hz. If its length is 33 cm, then find the velocity of sound in air.

  1. $390 {ms}^{-1}$
  2. $160 {ms}^{-1}$
  3. $330 {ms}^{-1}$
  4. $150 {ms}^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For a closed pipe, the fundamental frequency f = v / (4 * L). Given f = 250 Hz and L = 33 cm = 0.33 m, v = f * 4 * L = 250 * 4 * 0.33 = 1000 * 0.33 = 330 m/s.