Transistors are used for the?

Analyze the question: It asks about the main use of a transistor, which is a semiconductor device.

Explain the concept: A transistor is a three-terminal semiconductor device (emitter, base, collector). It has two main uses:

1. Amplifier: a small change in base current produces a large change in collector current, which strengthens weak signals (e.g. in radios and public address systems).
2. Switch: it turns current on or off, as in digital circuits.

Check each option:

• A. Rectification of signals: Rectification is done by diodes, which allow current in one direction only. A transistor is not used for this.
• B. Conversion of a.c. to d.c.: This is also rectification, done by diodes (usually with a smoothing capacitor). It is not the transistor's job.
• C. Amplification of signals: This is the transistor's main function. A small input signal at the base controls a larger current in the collector circuit, so the output signal is stronger.
• D. Conversion of d.c. to a.c.: This is the job of an inverter or an oscillator circuit. Transistors can be components in these circuits, but converting d.c. to a.c. is not their general purpose.

Answer: The correct option is C. amplification of signals.

Exam tip: Remember "Diode = Direction (rectifier), Transistor = Turn up (amplifier/switch)." If a JAMB question mentions rectification or a.c. to d.c., think diode. If it mentions amplification or switching, think transistor.