CBSE Class 11-science Answered

(i)  The oscillations in which the amplitude decreases progressively with the time are called damped oscillations.

(ii)  When we feed energy back to the oscillations at the same rate at which it is dissipated, then the amplitude of such oscillations would remain constant with the time.  These oscillations are called maintained or sustained oscillations.

(iii)  When an external periodic agent of frequency (n) is applied to an oscillator of natural frequency (n_o), the external agent is called the driver and the oscillating body is called the driven.  The driven oscillator ultimately settles down to the frequency of the driver.  Such oscillations that are forced upon the oscillator by the external periodic agent are known as the forced oscillations.

(iv)  When the frequency of the driver (n) approaches the frequency of the driven (n_o), then the amplitude of the forced oscillations (and hence power drawn) becomes quite large.  The driver and the driven are said to be in resonance.  The phenomenon of setting a body into vibrations with its natural frequency by another body vibrating with the same frequency is called resonance.