Which device is used to control a larger current by using a smaller current for operation?

• A. Diode
• B. Capacitor
• C. Transistor
• D. Switch

Answer: (C)

A transistor is used to control a larger current with a smaller one because it can amplify current. In a bipolar transistor, a small base current modulates a much larger current flowing from collector to emitter. The ratio of the output current to the input current, called current gain, is typically large, so a tiny control signal can drive a substantial load current. This amplification capability is why transistors are core to both amplifiers and switches. Other devices don’t provide this kind of current gain: a diode passes current but doesn’t amplify a small input current into a larger output current; a capacitor stores charge rather than producing a controlled current gain; a switch can start or stop current flow but doesn’t use a small control current to regulate a larger current in the same way a transistor does.