Question

Why are the regions of compressions and rarefactions of sound waves formed?
A. A sound wave undergoes diffraction behind obstacles.
B. The reflected sound wave at a fixed end interferes with the incident wave.
C. The longitudinal movement of air molecules produce pressure fluctuations.
D. The speed of the sound wave changes as it travels through a medium.

Answer 1

Hint : Sound waves are longitudinal waves where the particles in the medium move to and fro in the direction of propagation of the wave. It can also be called the pressure wave. Find out how a sound wave propagates.

Complete step by step answer:
Sound wave is a mechanical wave which moves through the medium due to the back and forth vibration of the particles in the medium. If the sound wave is moving through a medium, it will move the particles in the medium both in the direction of motion of the sound wave and in the opposite direction. The direction of motion of the particles is parallel to the direction of motion of the sound wave. This type of waves is called the longitudinal wave.

Soundwave is produced from the vibration of objects. Consider a tuning fork. A vibrating tuning fork produces longitudinal waves. As the tuning fork vibrates it pushes the air molecules back and forth. First it pushes the air molecules in one direction and creates a region 0f high pressure. Then due to its backward motion, a low pressure region is created which allows the same particle to move in both directions. Due to this, there will be regions where the particles are compressed and other regions where the particles are drifted away from each other. The regions of compressions are of high pressure while the regions of rarefaction are of low pressure.
So, we can say that the regions of compression and rarefaction of sound waves forms due to the longitudinal movement of air molecules produces pressure fluctuation.

The correct option is (C).

Note: The loudness of a sound wave depends on the energy of the vibration of sound waves. On the other hand, the pitch of a sound wave depends on the frequency of the vibration. The more is the frequency, the more the pitch of the sound.