A device which can vary the resistance without opening the circuit.

A device which can vary the resistance without opening the circuit.

• A. Capacitor
• B. Transformer
• C. Rheostat
• D. Inductor

Answer: (C)

The idea being tested is how to change current in a circuit without breaking the connection, by using a device that can vary resistance on the fly. A rheostat does exactly this. It’s a resistive element with a movable contact (the slider) that taps into different points along the element. Turning the control changes how much of the resistive path is in the circuit, so the resistance rises or falls while the circuit stays closed, directly altering the current. Capacitors store charge and present impedance that changes with frequency rather than offering a controllable resistance in a live circuit. Transformers change voltage and current through magnetic coupling and depend on turns and load, not on adjustable resistance in the path. Inductors store energy in a magnetic field and oppose changes in current, but they don’t provide a tunable resistance in the circuit.

The idea being tested is how to change current in a circuit without breaking the connection, by using a device that can vary resistance on the fly. A rheostat does exactly this. It’s a resistive element with a movable contact (the slider) that taps into different points along the element. Turning the control changes how much of the resistive path is in the circuit, so the resistance rises or falls while the circuit stays closed, directly altering the current.

Capacitors store charge and present impedance that changes with frequency rather than offering a controllable resistance in a live circuit. Transformers change voltage and current through magnetic coupling and depend on turns and load, not on adjustable resistance in the path. Inductors store energy in a magnetic field and oppose changes in current, but they don’t provide a tunable resistance in the circuit.