Question

Assertion: Sound waves cannot travel in vacuum but light can travel in vacuum
Reason: Sound waves are longitudinal waves and they cannot be polarised but electromagnetic waves are transverse and they can be polarized.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Answer 1

Hint: Sound waves travel through compressions and rarefactions and hence they need molecules which can travel through these distances while light does not need matter to travel. It travels with the help of imaginary particles called photons which do not need to get compressed.

Complete step by step answer:
Water waves and sound waves are examples of mechanical waves. Light waves are not considered mechanical waves because they don't involve the motion of matter. Light waves are types of electromagnetic waves. Light waves can propagate through vacuum as they do not disappear after some time and hence do not require medium for propagation. However, sound waves are types of mechanical waves. Sound waves require a medium for its production and propagation. Sound waves are produced due to the vibrations of molecules of medium and as there is no matter in space the sound waves cannot propagate in vacuum. An electromagnetic wave transports its energy through a vacuum at a speed of about $3.00 \times 10^8$ m/s (commonly known as c), i.e. the speed of light.
The reason that only transverse waves can be polarised is that their vibrations can potentially occur in all directions perpendicular to the direction of travel. It is therefore possible to confine the vibrations to a single plane. Transverse: vibrations perpendicular to the direction of travel of the wave. Longitudinal: vibrations parallel to the direction of travel of the wave. Sound waves are longitudinal so they cannot be polarised.
Thus here, both the assertion and the reason are correct but reason is not the correct explanation for the assertion.

So, the correct answer is “Option B”.

Note:
Sound waves are a longitudinal wave which needs air pressure to travel and as there is no air in vacuum, sound does not travel in vacuum while light does not need a medium to travel. As they are made up of photons which are imaginary particles, light is only affected or deviated from its path through gravity, medium is not required.