The correct answer to this question is:
B. The brass on a bent bimetallic strip is on the outside curve
This is because a bimetallic strip is a popular temperature sensor that uses the expansion properties of two different metals to measure temperature. As the temperature changes, the longer alloy (called the baseline metal) heats up faster than the shorter alloy (the sensing metal). This difference causes the bimetallic strip to bend, aligning the two metals so that the sensing metal is on the outside curve of the bend. This bend is a clear indication of a temperature drop since the sensing metal has expanded while the baseline metal has not.
The other options are incorrect:
A. The alcohol in a thermometer expands: Alcohol expands when heated but this does not indicate a temperature drop in the thermometer. It simply means that the alcohol is hotter and has expanded.
C. The column of liquid in a thermometer moves up three degrees: This option describes the reading on a thermometer that uses a liquid column, not the actual temperature drop.
D. A bimetallic strip bends so that the steel is on the outside curve: This is the same as answer B and does not describe a temperature drop.
This question tests the understanding of how a bimetallic strip sensor works and how it indicates a change in temperature when it bends due to the expansion of different alloys in the strip.
