In a heat-activated switch using a bimetallic strip, what is the resulting action when the strip bends?

• A. It opens a contact switch.
• B. It grounds the circuit.
• C. It interrupts power to the power source.
• D. It closes a contact switch.

Answer: (D)

A heat-activated switch with a bimetallic strip works by converting temperature changes into a mechanical movement. Two metals with different expansion rates are bonded together; when heat is applied, one metal expands more than the other, causing the strip to bend or bow. In this design, the bending motion acts on a contact arm so that the movable contact is pressed into contact with the fixed contact, completing the circuit. When the strip cools and straightens, the contacts separate and the circuit opens. So the bending action of the heated strip results in closing a contact switch, allowing current to flow.