Question

How does a BJT act as a switch?

Answer 1

Hint: Generally, the transistor as a switch is the application of the device. A transistor is used for switching operation either for the opening or closing of the circuit. The operation of a transistor as a switch is based on its mode of operation. Here, the low voltage DC is turned on or off by transistors.

Complete answer:
A bipolar junction transistor (BJT) is a kind of transistor that uses both electrons and holes as charge carriers. The unipolar transistor is a kind of field-effect transistor, which uses only one kind of charge carrier.
A bipolar transistor only permits a small current injected at one of its terminals to manage a much larger current flowing between two other terminals, making the device capable of amplification or switching.
BJTs refer to two junctions between two semiconductor types, n-type and p-type, that are regions in a single crystal of material.
We can make the junctions in several different ways, like changing the doping of the semiconductor as it is grown, by depositing metal pellets to form alloy junctions.
A transistor has three modes: active region, cut-off region, and saturation region. During cut-off mode and the saturation mode, The transistor acts as a switch. The transistor is off during the cutoff region and becomes on during the saturation region.
Finally, A transistor can be used as a switch because a small electric current flowing through one part of here, causes a larger current flow through the other part of the transistor.

Note: Generally, a BJT is a three-terminal device. and it has two junctions.
The function of the transistor is to amplify the signal. The three terminals are base, emitter, and collector.
The transistor acts as a switch in the application of transistors.