Clinical thermometers are examples of

Step 1: Analyze the question The question asks which type of thermometer a clinical thermometer (the one used to measure body temperature) belongs to.

Step 2: The concept Thermometers are classified by the thermometric property they use:

• Pressure gas thermometer: uses the change in pressure of a gas at constant volume. It is used in laboratories and for very wide temperature ranges.
• Resistance thermometer: uses the change in electrical resistance of a metal wire, usually platinum. It is used in industry for precise measurements.
• Alcohol thermometer: uses the expansion of coloured alcohol. It is suited to very low temperatures because alcohol freezes at about -115°C.
• Mercury-in-glass thermometer: uses the expansion of mercury in a narrow glass capillary tube.

Step 3: Apply to the clinical thermometer The traditional clinical thermometer has these features:

• A glass bulb filled with mercury, connected to a narrow capillary tube.
• A constriction just above the bulb, which stops the mercury from falling back once it has risen. This lets you read the temperature after removing the thermometer from the body.
• A short range of about 35°C to 42°C, which covers normal and fever body temperatures.

These features make it a specialized mercury-in-glass thermometer.

Step 4: Answer The correct option is D. mercury-in-glass thermometer.

Exam tip: Remember "clinical = constriction + mercury". If a question mentions the kink or constriction, or a narrow range of 35-42°C, think mercury-in-glass. Also note that:

• Laboratory thermometers have a wider range, often -10°C to 110°C.
• Alcohol thermometers are for very cold places.
• Resistance thermometers are for precise industrial use.