How do transistors control the flow of electrical current?

Transistors control the flow of electrical current by acting as a valve, where a small input signal regulates a larger current flowing between two main terminals. Depending on the design, these terminals are known as the emitter and collector (in bipolar transistors) or the source and drain (in field-effect transistors).12

How Control is Achieved

• Bipolar Transistors: These devices use a third terminal, the base, to control current. By applying a small input voltage or current to the base, the transistor modulates the flow of charge carriers (electrons or holes) between the emitter and collector. A small change in the base input can result in a much larger change in the output current, allowing the device to amplify signals.32
• Field-Effect Transistors (FETs): These operate using an electric field. A voltage applied to the gate terminal creates an electric field that either attracts or repels charge carriers within a channel between the source and drain. This field effectively opens or closes the path for current, acting like a switch.451

In modern computing, transistors function primarily as high-speed switches, where the gate voltage determines if the circuit is "on" (conducting) or "off" (blocking current), representing binary 1s and 0s.16