A bimetallic thermometer works based on the principle of thermal expansion. It consists of two different metal strips or coils bonded together, each with different coefficients of thermal expansion. When the temperature changes, the two metals expand or contract by different amounts, causing the bimetallic strip to bend.

Here's how a bimetallic thermometer works:

1. Construction: A bimetallic thermometer typically consists of two metal strips or coils bonded together. These metals have different coefficients of thermal expansion, meaning they expand or contract at different rates when heated or cooled.

2. Bending Mechanism: As the temperature changes, one metal strip expands or contracts more than the other due to its coefficient of thermal expansion. This causes the bimetallic strip to bend or twist.

3. Pointer Movement: The bending of the bimetallic strip is connected to a pointer or indicator mechanism. As the strip bends, it moves the pointer across a scale, indicating the temperature.

4. Temperature Measurement: The scale on the bimetallic thermometer is calibrated to indicate the temperature corresponding to the amount of bending in the strip. By reading the position of the pointer on the scale, the temperature can be determined.

5. Hysteresis: Bimetallic thermometers may exhibit hysteresis, meaning the pointer may not return to exactly the same position when the temperature decreases after it has increased. This is due to the different rates of expansion and contraction of the two metals.

Bimetallic thermometers are simple, robust, and cost-effective devices used for temperature measurement in various applications, such as industrial processes, HVAC systems, appliances, and automotive applications. They provide a visual indication of temperature changes and are suitable for use in environments where electrical or electronic devices may not be appropriate or feasible.