What is meant by resonance? Describe a simple experiment to illustrate the phenomenon of resonance and explain it.

Resonance is a special case of forced vibrations.

When the frequency of the externally applied periodic force on a body is equal to its natural frequency, the body readily begins to vibrate with an increased amplitude. This phenomenon is known as resonance.

Experiment — Mount two identical tuning forks A and B, of the same frequency on two separate sound boxes such that their open ends face each other as shown in figure below.

When the prong of one of the tuning forks say, A is struck on a rubber pad, it starts vibrating. On putting the tunning fork A on its sound box, we find that the other tuning fork B also starts vibrating and a loud sound is heard.

The vibrating tuning fork A produces the forced vibration in the air column of its sound box. These vibrations are of large amplitude because of large surface area of air in the sound box.

These vibrations are communicated to the sound of the fork B. The air column of B starts vibrating with the frequency of fork A. Since the frequency of these vibrations is same as the natural frequency of the fork B, the fork B picks up these vibrations under resonance.