Question

describing thermostats
in a thermostat, what property of the bimetallic coil allows it to contract and expand?
the two metals absorb different amounts of thermal energy.
the two metals are placed perpendicular to each other.
the two metals burn at different temperatures.
the two metals turn into liquids when absorbing energy.

Explanation:

A bimetallic coil in a thermostat consists of two different metals bonded together. Different metals have different coefficients of thermal expansion. When heat (thermal energy) is absorbed, the metal with a higher coefficient of thermal expansion will expand more than the other metal. This differential expansion (due to absorbing different amounts of thermal energy and having different expansion rates) causes the coil to bend (contract or expand depending on the temperature change). The orientation (perpendicular or not as in option 2) is not the key property for contraction/expansion. Burning (option 3) and melting (option 4) are not relevant to the normal operation of a thermostat's bimetallic coil which works within temperature ranges where the metals remain solid.

Answer:

The two metals absorb different amounts of thermal energy.