Which component is commonly used to provide protection against voltage surges in electrical circuits?

The component that is commonly used to provide protection against voltage surges in electrical circuits is the varistor. A varistor is a voltage-dependent resistor that exhibits a nonlinear resistance characteristic, which allows it to clamp voltage spikes and transients effectively. When a surge occurs, the resistance of the varistor decreases, allowing excess energy to dissipate safely through the device rather than passing through sensitive circuit components. This property makes varistors particularly effective for protecting circuits from high-voltage transients caused by events like lightning strikes or electrical switching.

Other components listed, such as diodes, transistors, and capacitors, serve different functions. Diodes are primarily used for directing current flow and protecting against reverse polarity, but do not provide the same level of surge protection as varistors. Transistors act as switches or amplifiers in electronic circuits but do not have the capability to absorb voltage surges. Capacitors can filter out AC noise and provide power smoothing, but they do not specifically protect against voltage spikes in the way that varistors do. Thus, while all these components play important roles in electronic circuits, the varistor is specifically designed for surge protection.