Explain how transistor acts as an amplifier - M R Academic Care

A transistor raises the strength of a weak signal and thus acts as an amplifier.  The basic circuit of a transistor amplifier. The weak signal is applied between emitter base junction and output is taken across the food RC connected in the collector circuit.

As the input circuit has low resistance, therefore, a small change in signal voltage causes an appreciable change in emitter current. This causes almost the same changes in collector current. The collector current flowing through a high load resistance RC produces a large voltage across it. Thus a weak signal applied in the input circuit appears in the amplified form in the collector circuit. It is in this way that a transistor acts as an amplifier.

Example:

Suppose collector load resistance RC= 5KΩ.

Let, a change of 0.1V in signal voltage produces a change of 1 mA in emitter current. Obviously, the change in collector current would also be approximately 1 mA. 

This collector current flowing through the load RC would produce a voltage = 5KΩ × 1 mA = 5V

Thus a change of 0.1V in the signal has caused a chance of 5V in the output circuit. So voltage amplification =

𝑉𝑜𝑢𝑡𝑆𝑖𝑔𝑛𝑎𝑙 = 5𝑉0.1𝑉 = 50 times