How is a bimetal constructed?

A bimetal is constructed by using two dissimilar metals with different expansion ratings. This specific combination allows the bimetal to take advantage of the differing thermal expansion rates of the two metals. When the bimetal is heated, the metal with the higher expansion rate will expand more than the metal with the lower rate, causing the bimetal to bend or curve. This property is extremely useful in various applications, such as thermostats and temperature sensors, where precise mechanical movement is required to activate or deactivate a circuit based on temperature changes.

The other options do not accurately describe the construction of a bimetal. A single metal alloy would not provide the necessary difference in expansion rates needed for the bimetal effect. A metal coated with ceramic does not involve two dissimilar metals that respond differently to heat. Lastly, plastic and metal combined might suggest a composite material but lacks the fundamental principle of thermal expansion that defines a bimetal.