Question

Three statements regarding the propagation of sound waves.

I Sound waves propagate through a series of crests and troughs.

II Sound waves require a material medium for their propagation.

III The propagation of sound waves is attributed to the motion of particles.

Among the given statements,

• A. only I is incorrect
• B. only III is incorrect
• C. both I and II are incorrect
• D. both II and III are incorrect

Answer 1

The correct option is A

only I is incorrect

Sound is produced by an object in vibration. The disturbance created by sound causes its neighbouring particles to vibrate. As the vibration moves forward, it pushes the air particles present in front of it. It results in the creation of a high pressure region called compression. When the vibrating object moves backward, it creates a region of low pressure called rarefaction. Hence, a series of compressions and rarefactions are produced, thereby causing the sound wave to propagate through air. This is shown in the following figure.

Crests and troughs are the essential features of transverse waves. Since sound is a longitudinal wave, it can never have such features. Hence, statement I is incorrect.