What component typically has three terminals including a movable contact?

• A. Variable resistor
• B. Capacitor
• C. Inductor
• D. Transformer

Answer: (A)

A three-terminal device with a movable contact is a potentiometer, a type of variable resistor. It consists of a resistive element with two fixed ends, plus a wiper that slides along the element. The three terminals are the two ends and the wiper. As you turn the knob, the wiper moves to tap a different point on the track, changing how much resistance is on each side and providing a variable output voltage when used as a voltage divider. This setup is ideal for adjustable levels like volume control or tuning.

Capacitors and inductors don’t use a sliding contact to pick off a variable portion of a single element, so they don’t fit the description. A transformer involves windings and taps but not a movable contact that continuously changes the connection along a single element, so it also isn’t the typical three-terminal with a movable contact.