Describe briefly the underlying principle of a transistor amplifier working as an oscillator. Hence, use the necessary circuit diagram to explain how self sustained oscillations are achieved in the oscillator.

Explanation

A portion of output power is returned at the input in same phase as that of starting power, hence the output in the oscillator gets self sustained. This is termed as positive feedback.

As the switch `S_1` is closed, a surge of collector current flows through coil `T_2`, which causes a changing magnetic flux around it. Hence a portion of the output is feedback to the coil `T_1` as a result of the positive feedback. The emitter current, therefore, starts oscillating