Why transistor act as amplifier?

Amplification is the process of linearly increasing the amplitude of an electrical signal.
- A transistor can act as an amplifier directly using the gain, b.
- Keep in mind that when a transistor is biased in the active (linear) region, the BE junction has a low resistance due to forward bias and the BC junction has a high resistance due to reverse bias.
i) DC and AC quantities
- Amplifier circuits have both ac and dc quantities.
- Capital letters are used will be used for both ac and dc currents.
- Subscript will be capital for dc quantities.
- Subscript will be lowercase for ac quantities.
ii) Transistor amplification
- A transistor amplifies current because the collector current is equal to the base current multiplied by the current gain, b.
- Base current (IB) is small compared to IC and IE.
- Thus, IC is almost equal to IE.