The sensitivity of a thermometer is

1. Analyze the question

The question asks for the definition of "sensitivity" in the context of a thermometer. In physics, sensitivity refers to how responsive an instrument is to small changes in the quantity it is designed to measure.

2. Explain the concept

In measurement science, sensitivity is defined as the ratio of the change in the output (the reading on the thermometer, such as the length of a liquid column) to the change in the input (the temperature).

A highly sensitive thermometer is one that shows a large, noticeable change in its reading for even a very tiny change in temperature. Therefore, the "sensitivity" is essentially determined by the smallest increment of temperature that the device can reliably detect or measure.

• Option B describes responsiveness (how fast it reacts), not sensitivity.
• Option C describes the range of the thermometer.

3. Show the solution

• Sensitivity = $\frac{\text{Change in output}}{\text{Change in input}}$
• If a thermometer has high sensitivity, a very small change in temperature (input) will produce a measurable change in the liquid level (output).
• Therefore, the limit of this sensitivity is the smallest temperature change that the thermometer can detect. If the temperature changes by an amount smaller than this limit, the thermometer will not show any change, meaning it is not sensitive enough to detect it.

4. Identify the answer

Based on the definition of sensitivity in physical instruments, the correct description is the smallest temperature change that can be detected or measured. This matches Option D.

5. Tip

Think of sensitivity as "precision in detection." If you are using a clinical thermometer, you want it to be very sensitive so that it can detect a tiny fever (e.g., 0.1°C difference). If the thermometer could only measure in whole numbers, it would have low sensitivity!