Working of Transistor as an oscillator
Since a transistor mainly transfers the resistance, it is called as transistor.
There exists an input circuit with a small source of power and a small resistance and an output circuit with a high resistance and moderately large source of power.
In the input circuit, whenever there is a small change in current, there is an amplified variation of current in the output circuit, mainly because the resistances are transferred.
The amplified output current also oscillates with respect to the input, When the input current is made to oscillate by applying a signal to the input terminal,
How a transistor works as an amplifier.
Analogy: If we shake the pole here and there, just fix a long wooden pole on the ground. We can monitor that the top of the pole is shaking dynamically.
An amplifier can be made an oscillator by a simple way.
When the transistor is working as an amplifier, a small portion of the out power (oscillating current) is taken and it is feed to the input section. Simultaneously remove the input signal which we used for the amplification process.
For the amplifier, the input signal is got from its output and that is amplified. Also a portion of the output is again sent to the input and the process is continued. This is how the amplifier now works as an oscillator.
For the proper function of oscillator, a proper portion of the output and the phase of output is important.