# Which of the following are the functions of a transistor?

Which of the following are the functions of a transistor?

### Right Answer is: Variable resistor and switching device

#### SOLUTION

The transistor is a semiconductor device made by joining together three layers of P and N-type material.

Operating a transistor

When you design a transistor circuit, you choose components that will put the transistor into the right operating mode (cutoff, active, or saturation), depending on what you want the transistor to do. Here’s how:

Transistor as a variable Resistor:- The operation of a transistor could be explained by making an analogy to faucets.

The emitter is the source (as in the water supply). The handle of the faucet is equal to the base whereas the end of the opening where water will flow from is the equal of the collector. In a transistor, the collector is the output whereas the emitter is the input This leaves the base as the controller of current between the emitter and collector.

By applying a high enough voltage to the base (like exerting pressure on a faucet handle), you switch the transistor on, and current flows from the collector to the emitter (like the water flows through the pipe part of the faucet). If the voltage at the base is too low, you switch off the transistor, and no current flows from the collector to the emitter.

When the transistor is switched on, you control the amount of current that flows from the collector to the emitter by controlling how much current flows into the base of the transistor. And the nice part about this fact is that small currents in the base control large currents flowing from the collector to the emitter.

It is correctly said that the transistor is nothing but the variable resistor. The resistance between collector and emitter depends upon the base current. Higher is the base current lower is the resistance between collector and emitter and at that time transistor is said to be in ON state.

Collector current, IC = β × Ib(base current)

Transistor amplifier: if you want to use the transistor as an amplifier (active model, you select supply voltages and resistors to connect to the transistor so that you forward-bias the base-emitter junction and allow just enough base current to flow—but not so much that the transistor becomes saturated. This selection process is known as biasing the transistor.

Transistor switch: If you want the transistor to act like an on/off switch, you choose values of supply voltages and resistors so that the base-emitter junction is either nonconducting (the voltage across it is less than 0.7 V) or fully conducting—with nothing in between. When the base-emitter junction is nonconducting, the transistor is in cutoff mode and the switch is off. When the base-emitter junction is fully conducting, the transistor is in saturation mode and the switch is on.

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