Tag: physics

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Questions Related to physics

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

You see lightning before you hear the thunder because

  1. Lightning is much brighter than thunder.

  2. Thunder is heavier than lightning.

  3. Light can travel through air but sound cannot.

  4. Sound travels slower than light.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Answer is D.

Lightning and thunder are produced simultaneously, but the thunder is heard a few seconds after the lightning is seen. This is because the speed of light in air is more than the speed of sound in air.The speed of light is given as $3\times { 10 }^{ 8 }m/s$. The speed of sound is 340 m/s.
Hence, the flash of lightning is seen before the thunder is heard as the speed of sound is less than 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.