Tag: comparison of speed of sound with speed of light

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Questions Related to comparison of speed of sound with speed of light

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

An observer measures speed of light to be C when he is stationary with respect to the source. If the observer moves with velocity $\displaystyle v$ towards the source then the velocity of light observed will be :

  1. $\displaystyle c- v$

  2. $\displaystyle c + v$

  3. $\displaystyle \sqrt{1-v^2/c^2}$

  4. $\displaystyle c$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Speed of light does not change with the frame of reference.  Option 'D' is correct.