Which device is commonly used to vary resistance without opening the circuit?

Which device is commonly used to vary resistance without opening the circuit?

• A. Ammeter
• B. Rheostat
• C. Ohmmeter
• D. Capacitor

Answer: (B)

To adjust how much resistance a circuit presents without breaking the path, a rheostat is used. It’s a two-terminal variable resistor that changes the effective resistance by sliding or rotating a contact along a resistive element, letting you tweak current while the circuit stays complete. This makes it ideal for applications like dimming lights or controlling motor speed where you need smooth, in-circuit adjustment. An ammeter, by contrast, is designed to measure current and is placed in series; it doesn’t adjust resistance. An ohmmeter measures resistance but must be used with the circuit de-energized and isolated from the rest of the circuit. A capacitor stores electric energy and serves functions like filtering or timing rather than controlling resistance.

To adjust how much resistance a circuit presents without breaking the path, a rheostat is used. It’s a two-terminal variable resistor that changes the effective resistance by sliding or rotating a contact along a resistive element, letting you tweak current while the circuit stays complete. This makes it ideal for applications like dimming lights or controlling motor speed where you need smooth, in-circuit adjustment.

An ammeter, by contrast, is designed to measure current and is placed in series; it doesn’t adjust resistance. An ohmmeter measures resistance but must be used with the circuit de-energized and isolated from the rest of the circuit. A capacitor stores electric energy and serves functions like filtering or timing rather than controlling resistance.