Remote-controlled power switching — which device below can be rapidly switched ON and OFF by a separate low-power control circuit to drive an AC load?

Introduction / Context:
Industrial and consumer AC power controls often need a solid-state “electronic switch” that a low-power control signal can trigger repeatedly and quickly. Several components appear in such circuits, but only some perform the actual high-current switching of the load under control of a small signal.

Given Data / Assumptions:

• Load: AC mains lamp, heater, or motor.
• Control: a small trigger voltage or current from a timing or logic circuit.
• Device must carry load current and be triggerable remotely.

Concept / Approach:
A triac is designed to conduct substantial AC load current and can be turned on by a gate signal from a low-power controller. It latches on per half-cycle and turns off naturally at current zero-crossing. A diac, while related, is a bidirectional trigger device (breakover diode) used to fire a triac, not to carry heavy load current on its own. An RTD is a temperature sensor, not a switch. A “zero-voltage switch” describes a control strategy or a specialized module that switches at AC zero crossing to reduce electromagnetic interference; the underlying power element inside such modules is often a triac or SSR, but the basic component-level answer is “triac.”

Step-by-Step Solution:

Verification / Alternative check:
Standard light dimmer schematics show a diac triggering the gate of a triac; the triac is the element that actually switches the load current.

Why Other Options Are Wrong:

• Diac: trigger only; not rated to carry large AC load continuously.
• RTD: temperature sensor; cannot switch AC loads.
• Zero-voltage switch: describes switching timing; underlying device is typically a triac or SSR module.

Common Pitfalls:
Confusing the trigger (diac) with the main power switch (triac); assuming a marketing term (“zero-voltage switch”) is itself a discrete component.

Final Answer:
Triac.