Alberta Boilers Safety Association (ABSA) Practice Test

In a bimetal thermometer, the design relies on two different types of metals that are bonded together. The key principle behind its operation is the difference in thermal expansion rates of the two metals when exposed to temperature changes. Each metal expands and contracts at a different rate, which creates mechanical movement.

For this reason, having a large difference in their coefficient of expansion is essential. When one metal expands more than the other in response to heat, the resulting curvature of the bimetallic strip can be used to move a pointer on a scale, indicating the temperature. This differential expansion is what makes the instrument functional and sensitive to temperature changes.

The other choices, while related to material properties, do not directly contribute to the bimetal thermometer’s functionality. Electrical conductance and resistance do not play a role in the temperature measurement process in this type of thermometer; thus, they are not relevant to the operation of a bimetal thermometer.