Question

derivation of transistor as amplifier

Answer 1

We can use a transistor as an amplifier by raising the strength of the weak signal. With the help of suitable diagram, we explain you how transistor circuit acts as an amplifier. The Figure given below shows the basic circuit of a transistor amplifier.

We apply input signal or the weak signal between the emitter-base junction and takes the output across the load Rc connected in the collector circuit. For faithful amplification, always ensure that the input circuit is forward-biased and the output circuit is reverse-biased. For this purpose, we apply d.c voltage i.e. VEE in the input circuit in addition to the signal as shown in the figure above. This d.c voltage is known as a bias voltage and its magnitude is such that it always keeps the input circuit forward biased despite the polarity of the signal.

As we know the input circuit has low resistance, consequently, a small change in the signal voltage occurs at the input circuit lead to an appreciable change in the emitter current. Due to transistor action, change in emitter current causes a similar change in the collector circuit. Now, the collector current flowing through a high load resistance Rc produces a large voltage across it. Thus, the weak signal applied in the input circuit appears in the amplified form in the collector circuit. In this way, transistor acts an amplifier.