Assertion`:` A vibrating tuning fork sounds louder when its stem is pressed against a desk top.
Reason `:` When a wave reaches another denser medium, part of the wave is reflected.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

C

Explanation

If the tuning fork is held in hand and hit with hammer, a sound is produced as the prongs of the tuning fork set surrounding air particles into vibrational motion. The sound produced by the tuning fork in air is barely audible. However, if the tuning fork is set on a desktop. The desktop begins vibrating at the same natural frequency of the tuning fork. The tuning fork forces surrounding desktop particles into vibrational motion. The vibrating desktop in turn forces surrounding air particles into vibrational motion. As the surface area of desktop is greater than the surface area of tuning fork, more surrounding air particles will be forced into vibration. This causes an increase in the amplitude and thus loudness of the sound.