Wave Motion - Short Questions With Answer | Physics Class 12

Short Answer Question | Physics
Short Question-Answer form Wave Motion
Class: 12

1. Differentiate between forced vibration and free vibration.

The free vibration and forced vibration can be differentiated by the following points: A body is said to execute free vibration when it is vibrating by itself, while a body is said to execute forced vibration, when it is compelled to vibrate by a periodic force at a frequency other then its natural frequency. A body in free vibration vibrates with its natural frequency while in forced vibration it vibrates with the frequency of the source. A body in free vibration vibrates with the help of internal elastic forces while in forced vibration it vibrates with the help of external periodic force. Free vibration is self-sustained vibration while forced vibration while forced vibration is externally sustained vibration.

2. How are stationary waves formed?

When two progressive waves of the same wavelength and amplitude travel with the same speed through a medium in opposite directions, they superimpose upon each other and thus a wave is formed which is stationary wave. When a stationary wave is formed, points of maximum and minimum, (zero) amplitudes are resulted alternately in space.

3. If you are walking on the moon surface, can you hear the cracking sound behind you? Explain.

No, we can’t hear the cracking sound behind us, if we are walking on the moon surface. This is so because there is no atmosphere on the moon. So there is lack of medium for the propagation of sound waves on the moon. As we know that sound waves need medium for propagation, it cannot propagate in vacuum.

4. Why are longitudinal wave not polarized?

Longitudinal wave are not polarized because they are the waves in which the vibration of particles takes place in the direction of motion of waves. Thus, the longitudinal wave is already polarized in the direction of motion of wave. So, longitudinal waves aren’t polarized.

5. Do sound waves undergo reflection, refraction and polarization phenomena? Explain.

Being a wave, the wave undergoes reflection and refraction. These phenomena are exhibited by both transverse wave and longitudinal wave. But, polarization phenomena are exhibited by transverse wave only. Since the sound wave is longitudinal wave, so it doesn’t exhibit polarization phenomenon.

6. Which types of wave propagate in liquid, explain.

Both transverse wave and longitudinal wave are possible in liquid. Between these two waves, major component of the wave is longitudinal which dominates transverse wave. A liquid can have bulk modulus of elasticity but it doesn’t have modulus of rigidity.

7. Distinguish between light waves and sound waves.

The following points distinguish between light wave and sound waves:

Light Waves	Sound Waves
They are elector magnetic waves.	They are mechanical waves.
They do not need material medium for their propagation. i.e. they can propagate even in vacuum.	They need material medium for their propagation but the material particles are not carried by the wave.

8. A radio station broadcasts at 800 KHz. What will be the wavelength of the wave?

Given, frequency of sound wave (f) = 800 KHz =800000 Hz

Also, we know velocity of sound in air (v)=332 m/s

Then, the wavelength of the wave is given by 

λ =v/f = 332/800000 =4.15×10-4 m

Hence, the wavelength of the wave will be 4.15×10-4 m if a radio station broadcasts at 800 KHz.

9. What are differences between transverse and longitudinal wave?

Transverse waves	Longitudinal waves
The particles of the medium vibrate in the direction perpendicular to the direction of wave propagation.	The particles of the medium vibrate parallel to the direction of wave propagation.
Alternate crests and trough are formed.	Alternate compression and rarefaction of the medium are formed.
These are formed in solids and over liquid surfaces.	These are formed in solids, liquids and gases.
These waves produce the variations in the density of medium.	These waves do not produce variations in the density of the medium.
Transverse waves can be polarized	Longitudinal waves cannot be polarized.

10. What are the differences between progressive waves and stationary waves?

Progressive waves	Stationary waves
The disturbance travels forward	The disturbances are confined to a particular region.
The amplitude of vibration of each particle is same.	The amplitude is zero at nodes and goes on increasing and becomes maximum at antinodes.
Energy is transferred forward along the waves.	No transfer of energy is in the medium
No particles in the medium are at rest.	Particles at the nodes are permanently at rest.

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