# What is Resonance?

## Definition:

Resonance occurs when the frequency of the applied periodic forced is equal to one of the natural frequencies of vibration of the forced or driven harmonic oscillator.

## Explanation:

Associated with the motion of a driven harmonic oscillator, there is a very striking phenomenon, known as resonance.It arises if the external driving force is periodic with a period comparable to the natural period of the oscillator.

In a resonance situation, the driving force may be feeble, the amplitude of the motion may become extra ordinarily large. In the case of oscillating simple pendulum, if we blow to push the pendulum whenever it comes in front of our mouth, it is found that the amplitude steadily increases.

To demonstrate this resonance effect, an apparatus is shown in Fig. A horizontal rod AB is supported by two strings S1 and S2. Three pairs of pendulums aa’, bb’and cc’ are suspended to this rod. The length of each pair is the same but is different for different pairs. If one of these pendulums, say c, is displaced in a direction perpendicular to the plane of the paper, then its resultant oscillatory motion causes in rod AB a very slight disturbing motion, whose period is the same as that of c’. Due to this slight motion of the rod, each of the remaining pendulums (aa’ bb’.and cc’) under go a slight periodic motion. This causes the pendulum c’, whose length and, hence, period is exactly the same as that of c, to oscillate back and forth with steadily increasing amplitude. However, the amplitudes of the other pendulums remain small through out the subsequent motions of c and c’, because their natural periods are not the same as that of the disturbing force due to rod AB. The energy of the oscillation comes from the driving source. At resonance ,the transfer of energy is maximum.