I. High thermal capacity. II. High sensitivity. III.Easy readability. IV. Accuracy over a wide range of…

Analyze the question: We need to pick which of the four listed properties make a good thermometer.

Explain the concept: A thermometer should measure temperature without changing the temperature of the object being measured. It should also respond quickly and be easy to read.

Evaluate each statement:

• I. High thermal capacity: This is NOT a good quality. A thermometer with high thermal capacity absorbs a lot of heat from the object, which changes the temperature you are trying to measure. It also responds slowly. A good thermometer should have a low thermal capacity.
• II. High sensitivity: This is good. A small change in temperature should produce a noticeable change, such as a visible movement of the mercury thread.
• III. Easy readability: This is good. The scale should be clear, with a thin, visible thread.
• IV. Accuracy over a wide range of temperature: This is good. The thermometer should give reliable readings across a useful range.

Conclusion: Statements II, III and IV are qualities of a good thermometer. Statement I is wrong, so options A, B and C are eliminated.

Correct answer: D (II, III and IV).

Exam tip: Remember "thermometer = low thermal capacity". The thermometer must not take heat away from what it is measuring. Whenever an option says "high thermal capacity" for a thermometer, it is probably a trap.