Question

which causes an air conditioner to turn on?
house - temperature decreases cause the bimetallic coil to expand or contract
house - temperature decreases cause the bimetallic coil to return to normal
house - temperature increases cause the bimetallic coil to return to normal
house - temperature increases cause the bimetallic coil to expand or contract

Explanation:

An air - conditioner turns on when the house temperature increases. A bimetallic coil is used in the thermostat of an air - conditioner. Bimetallic strips are made of two different metals bonded together. Different metals have different coefficients of thermal expansion. When the temperature increases, the two metals in the bimetallic coil expand at different rates, causing the coil to expand or contract. This mechanical movement in the thermostat (due to the change in the bimetallic coil caused by temperature increase) completes the electrical circuit and turns on the air - conditioner.
When the temperature decreases, the bimetallic coil would return to its original state (if it was triggered by a temperature increase before) and turn off the air - conditioner.

Answer:

House - temperature increases cause the bimetallic coil to expand or contract.