A transistor is fundamentally a device for amplifying a signal. While it can increase current, voltage, or power depending on the circuit design, its core function is to boost a weak input signal into a stronger output signal.

Here is how a transistor achieves amplification in different ways:

• Current: For a bipolar junction transistor (BJT), a small current at the base terminal can control a much larger current flowing between the collector and emitter. This is one of the most direct forms of amplification.
• Voltage: By adding components like resistors, a transistor can amplify voltage. A small change in the input voltage causes a change in current, which then produces a much larger change in the output voltage across the load.
• Power: Since power is the product of voltage and current (\(P=VI\)), and a transistor can be configured to amplify both, it also acts as a power amplifier.

The overall purpose is to increase the strength of an electrical signal—whether it is a radio frequency, an audio signal, or another type of electrical input—before passing it on to the next part of the circuit.