CAPF AC 2022 Q11: Science & Technology – Physics
- (a) Register
- (b) Transistor
- (c) Flip-flop
- (d) Diode
Answer: (b) Transistor
Explanation
The device that amplifies a signal
How to think: to increase the power of a signal while keeping its shape is to amplify it.
The semiconductor device used as an amplifier is the transistor.
| Device | What it does |
|---|---|
| Transistor | Amplifies weak signals; also works as a switch |
| Diode | Lets current flow in one direction; used as a rectifier |
| Flip-flop | Stores one bit of data |
| Register | A group of flip-flops storing several bits |
About the transistor: it has three regions, the emitter, base and collector.
A small change in the base current gives a large change in the collector current.
It was invented at Bell Laboratories in 1947 by Bardeen, Brattain and Shockley.
Answer: (b) Transistor.
Why each option is right or wrong
- (a) Incorrect. A register stores data bits; it does not amplify.
- (b) CORRECT. A transistor amplifies a signal without changing its shape.
- (c) Incorrect. A flip-flop is a memory element that stores one bit.
- (d) Incorrect. A diode only allows one-way flow and is used for rectification.
Key point
Transistor: amplifier and switch; emitter, base, collector; invented 1947 (Bardeen, Brattain, Shockley; Nobel Prize 1956). Diode: rectifier. Flip-flop: one-bit memory. Register: group of flip-flops.
Remember
Transistor amplifies; diode rectifies.
Common mistakes
- Marking the diode, which rectifies current but cannot amplify it.
- Mixing up a register (storage) with a resistor or a regulator.
- Forgetting that amplification means the output is a bigger copy of the input.
Exam tip
Educated guess: the old pocket radio was called a transistor because it used transistors to amplify weak radio signals.
Sources
- NCERT Class XII Physics — Semiconductor Electronics: Materials, Devices and Simple Circuits
- NCERT Class XI Computer Science — Computer System (memory, registers and flip-flops)