Which device regulates the strength of an electrical current?

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

Answer: (C)

Regulating the strength of an electrical current is achieved by changing the circuit’s resistance. A rheostat is a variable resistor designed for this purpose: by turning its knob, you change the length of resistive material in the path, which alters the resistance. According to Ohm’s law (I = V/R), increasing resistance lowers current and decreasing resistance raises current, so the rheostat directly controls the current level.

A transformer, on the other hand, changes voltage and current levels between circuits but doesn’t regulate current by itself; its effect depends on the load and source. A capacitor stores energy and affects current mainly by charging and discharging, especially in AC circuits, rather than actively regulating steady current. A generator provides electrical power but does not regulate the current in a circuit.