Which of the following thermometer types best responds to a change in temperature

Analysis

The question asks us to identify which type of thermometer is most sensitive, meaning it reacts most quickly and accurately to small or rapid changes in temperature.

Concept Explanation

Sensitivity in a thermometer refers to its ability to detect and respond to minute changes in temperature. This depends on:

1. Thermal Capacity: A thermometer with a low thermal capacity absorbs very little heat from the body being measured, allowing it to reach thermal equilibrium faster.
2. Thermal Conductivity: The material must be able to transfer heat quickly from the source to the sensing element.
3. Response Time: This is the time taken for the thermometer to register the temperature of the object it is measuring.

Step-by-Step Solution

• Mercury and Alcohol thermometers: These rely on the expansion of liquid in a glass bulb. Because the glass bulb has a relatively high thermal capacity and the liquid takes time to expand and move up the capillary tube, these are generally slower to respond to rapid temperature changes.
• Gas thermometers: These are highly accurate but are bulky and slow to reach equilibrium because they require a large volume of gas to be heated. They are typically used for calibration purposes rather than quick measurements.
• Resistance thermometers: These use a fine wire (usually platinum) wound around a frame. Because the wire is very thin and has a very low thermal capacity, it gains or loses heat almost instantaneously when placed in contact with a medium. This allows it to respond to temperature changes much faster than liquid-in-glass thermometers.

Conclusion

Among the options provided, the resistance thermometer is the most sensitive and has the fastest response time to changes in temperature.

Exam Tip: Remember that "sensitivity" in physics often relates to how quickly a device can detect a change. If you see a question about "fast response" or "high sensitivity" in thermometry, always look for the device with the smallest thermal mass (like a thin wire in a resistance thermometer or a thermocouple).