Visual Testing (VT) Practice Exam

What fundamental principle allows a bimetallic thermometer to operate?

1. Metals change volume with temperature changes

2. Metals have the same coefficients of expansion

3. Thin strips of different metals are placed next to each other

4. All of the above

The correct answer is: Metals change volume with temperature changes

The functioning of a bimetallic thermometer is based on the principle that different metals expand at different rates when subjected to temperature changes. This is due to the unique physical properties of each metal, particularly their coefficients of thermal expansion, which represent how much a material expands per degree of temperature change. In the case of a bimetallic thermometer, two strips of different metals are bonded together. As the temperature rises or falls, one of the metals expands more than the other due to its higher coefficient of expansion. This difference in expansion causes the bimetallic strip to bend in a specific direction, allowing the movement to be translated into a measurement that indicates the temperature. While it is true that the other statements hint at various aspects of how a bimetallic thermometer is constructed, the fundamental operation relies primarily on the varied expansion properties of metals. This differential expansion is what causes the mechanical movement within the thermometer, making it possible for it to indicate temperature changes.