(1) Any vibrating object has a natural frequency, which depends on factors such as the elasticity and shape of the object.Whenever an object or a system is set in oscillation, at its natural frequency, as a result of impulses received from some other system vibrating with the same frequency, resonance is said to have occured. Resonance can occur in different kinds of system : acoustical,mechanical, electrical and optical. Resonance results in increased amplitude of vibration.The maximum displacement of the particles of the medium from their original undisturbed positions, when a wave passes through the medium, is called amplitude of wave.