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How can a transistor amplify an electrical signal?

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NMOS transistorNegative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors. — transistor NMOS transistor
Negative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.

A transistor amplifies an electrical signal by using a small input current to control a much larger output current.12

In a typical common-emitter configuration, the device is biased with a small forward voltage at the base-emitter junction and a larger reverse voltage at the base-collector junction. When an alternating current (AC) signal is applied to the base, it causes the base current to fluctuate. Because the transistor is designed so that a large number of charge carriers (electrons or holes) pass from the emitter to the collector for every carrier that passes to the base, these small fluctuations in the input signal result in proportionally larger variations in the collector current.12

This varying collector current flows through a series resistor, creating a voltage drop that serves as an amplified version of the original input signal. By effectively acting as a current-controlled switch or valve, the transistor allows a low-power input to modulate a high-power output, providing the amplification necessary for electronic circuits.213