Final answer:
The correct option is 2. Bimetal sensing elements in thermostats commonly use a combination of brass and steel. Brass expands or contracts differently than steel in response to temperature changes, which results in the mechanical action needed for temperature control.
Step-by-step explanation:
Thermostats with bimetal sensing elements typically use a combination of either copper or brass and steel. Brass is an alloy made up of copper and zinc, known for its malleability, making it advantageous in varying applications such as musical instruments. Steel, well-known for its strength and durability, contrasts with brass in its thermal expansion properties, which is essential for the functioning of a bimetallic thermostat. Bimetallic thermostats work on the principle of thermal expansion.
When subjected to changes in temperature, brass, and steel will expand or contract at different rates. This difference causes the bimetal strip to bend or coil, triggering a mechanical response that can be used to control the temperature. Thus, the correct answer to the question is option 2) Steel. The unique properties of alloys like brass (copper and zinc) and the combination of brass and steel make them ideal for use in temperature regulation devices.