Question

Light can travel in vacuum but not sound, because
A. Speed of sound is very slow than light.
B. Light waves are electromagnetic in nature.
C. Sound waves are electromagnetic in nature.
D. Light waves are not electromagnetic in nature.

Answer 1

Hint: Sound waves are mechanical waves. That means it needs a medium to travel from one place to another. It is the vibrating motion of the air particles that we perceive as sound. Whereas, light is a perfect elastic wave which does not need medium to propagate.

Complete step by step answer:
Let us first understand how soundwaves are created. When there is an oscillation in the air pressure at a certain place, it makes the air particles undergo consecutive compression and expansion. These oscillations reach our ears and convert the mechanical energy of the waves to the electrical energy of the pulses which are feeded to the brain. This is what we perceive as sound.

Hence, sound waves need a material to propagate from one place to another. As vacuum does not have a medium, sound waves cannot propagate in vacuum.

Light waves are significantly different from sound waves. Light waves are electromagnetic waves which do not require a medium to travel from one place to another. Fast vibration of charged particles is responsible for the origin of electromagnetic waves. These longitudinal waves have wave properties and matter properties. So, they do not need a medium for propagation.

So, the correct choice is - (B).

Note: Option (A) is also a true statement. Velocity of sound is less than the speed of light. However, this is not the reason behind the question. Velocity of sound depends on the medium of propagation. Speed of sound is maximum inside a solid, and minimum in air.