Oscillator is a circuit that generates signals of de sired frequencies and an amplifier is used to amplify the signals. Why positive feedback is applied in an oscillator?

Oscillator is a circuit that generates signals of de sired frequencies and an amplifier is used to amplify the signals.When transister is used as an amplifier, common emitter configuration is used. Why?

Oscillator is a circuit that generates signals of desired frequencies and an amplifier is used to amplify the signals. Draw a circuit diagram common emitter characteristics. Draw output characteristics for two in put current.