Which component is a two-terminal resistor used to control current and can adjust lamp brightness or speed?

Which component is a two-terminal resistor used to control current and can adjust lamp brightness or speed?

• A. Resistor
• B. Variable Resistor
• C. Thermistor
• D. Transformer

Answer: (B)

Controlling current by changing resistance is what a variable resistor does. Because it has two terminals, it can be wired in series with a lamp or motor, and you can turn its knob to change the resistance. Increasing the resistance lowers the current, dimming the lamp or slowing the motor, while decreasing the resistance raises the current and increases brightness or speed. A fixed resistor stays at one value and cannot adjust the current, so it can’t tune brightness or speed. A thermistor changes resistance based on temperature, not by user adjustment, so it isn’t suitable for direct, manual control of brightness or speed. A transformer alters voltage and current through magnetic coupling and isn’t used as a simple, adjustable current limiter. So the best choice is the variable resistor.

Controlling current by changing resistance is what a variable resistor does. Because it has two terminals, it can be wired in series with a lamp or motor, and you can turn its knob to change the resistance. Increasing the resistance lowers the current, dimming the lamp or slowing the motor, while decreasing the resistance raises the current and increases brightness or speed. A fixed resistor stays at one value and cannot adjust the current, so it can’t tune brightness or speed. A thermistor changes resistance based on temperature, not by user adjustment, so it isn’t suitable for direct, manual control of brightness or speed. A transformer alters voltage and current through magnetic coupling and isn’t used as a simple, adjustable current limiter. So the best choice is the variable resistor.