A device to vary the resistance and consequently create load on an electrical circuit.

A device to vary the resistance and consequently create load on an electrical circuit.

• A. Battery
• B. Carbon pile
• C. Capacitor
• D. Brush

Answer: (B)

Adjustable resistive loading is the idea here: you use a device whose resistance can be changed to create a controllable load on a circuit. A carbon pile is exactly that. It’s a stack of carbon discs with a mechanism to apply pressure. When you press harder, more disc-to-disc contact occurs, lowering the overall resistance and drawing more current at a given voltage. This lets you set a specific load to test how a power source or circuit behaves under different current demands. It’s particularly useful for high-current testing because the carbon pile can handle large currents while offering a tunable, stable load. By contrast, a battery is a source, not a load; a capacitor stores energy and behaves differently (not a steady resistive load); and a brush is a mechanical contact in motors/generators, not a load device.

Adjustable resistive loading is the idea here: you use a device whose resistance can be changed to create a controllable load on a circuit. A carbon pile is exactly that. It’s a stack of carbon discs with a mechanism to apply pressure. When you press harder, more disc-to-disc contact occurs, lowering the overall resistance and drawing more current at a given voltage. This lets you set a specific load to test how a power source or circuit behaves under different current demands. It’s particularly useful for high-current testing because the carbon pile can handle large currents while offering a tunable, stable load. By contrast, a battery is a source, not a load; a capacitor stores energy and behaves differently (not a steady resistive load); and a brush is a mechanical contact in motors/generators, not a load device.