*Question T6B03:
Which of these components can be used as an electronic switch?*  

*Correct Answer is  C: Transistor*  

### AI Response: (may contain errors)  

To determine which component can be used as an electronic switch, let's analyze each option:

### Correct Answer: Transistor
- **Explanation**: A transistor is a semiconductor device that can act as a switch or amplifier. When a small current flows into the base of a transistor, it allows a larger current to flow between the collector and emitter. This property makes transistors ideal for switching applications in electronic circuits.

### Why the Other Choices are Incorrect:
- **A: Varistor**  
  - **Explanation**: A varistor is a voltage-dependent resistor that changes its resistance based on the voltage applied across it. It is primarily used for voltage clamping and surge protection, not for switching.

- **B: Potentiometer**  
  - **Explanation**: A potentiometer is a variable resistor used to adjust voltage levels in a circuit. While it can control current flow, it does not function as a switch because it does not turn current on or off.

- **D: Thermistor**  
  - **Explanation**: A thermistor is a temperature-sensitive resistor. Its resistance changes with temperature, making it useful for temperature sensing and compensation, but it does not serve as a switch.

### Summary
- **Transistor**: Can be used as an electronic switch.
- **Varistor**: Used for voltage clamping.
- **Potentiometer**: Adjusts voltage levels, not a switch.
- **Thermistor**: Senses temperature, not a switch.

Understanding these distinctions will help you identify components and their functions in electronic circuits, which is crucial for the Extra Class exam.