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What is the difference between a clinical thermometer and a laboratory thermometer?

Class 6 ScienceNCERT chapter: Temperature and its Measurementइसे हिंदी में पढ़ें

Exam-ready answer

A clinical thermometer measures human body temperature and has a range of 35 °C to 42 °C. A laboratory thermometer measures the temperature of other objects, such as water, and usually has a range of -10 °C to 110 °C. A clinical thermometer keeps its reading after removal, but a laboratory thermometer must be read while still in the substance.

Explanation

Temperature tells us how hot or cold an object is, and it is commonly measured in degrees Celsius (°C). The human body temperature normally stays close to 37 °C, so a thermometer for the body needs only a narrow range. A clinical thermometer therefore reads from 35 °C to 42 °C. Today, digital clinical thermometers are widely used because the older ones contained mercury, which is poisonous.

A mercury clinical thermometer has a kink, a narrow bend just above the bulb. When the bulb is warmed in the mouth or armpit, mercury rises past the kink. When the thermometer is taken out, the kink stops the mercury from falling back, so the reading can be noted calmly. It must be jerked down before the next use.

A laboratory thermometer is used to measure the temperature of liquids and other objects in experiments, for example hot water in a beaker. Its wider range, about -10 °C to 110 °C, covers ice-cold to boiling water. It has no kink, so its reading falls as soon as it is taken out; it must be kept upright in the liquid, without touching the container, while reading.

Points to remember

  1. Clinical thermometer: measures human body temperature; range 35 °C to 42 °C.
  2. Laboratory thermometer: measures temperature of other objects; range about -10 °C to 110 °C.
  3. A mercury clinical thermometer has a kink that stops mercury from falling back on its own.
  4. A laboratory thermometer has no kink and must be read while its bulb is in the substance.
  5. Normal human body temperature is about 37 °C; temperature is commonly measured in degrees Celsius (°C).

Exam tip

Present the difference as a two-column table with rows for use, range, kink and how it is read. Always write the unit °C with every number, such as 35 °C to 42 °C.

Questions students also ask

Why should a clinical thermometer not be used to measure the temperature of boiling water?
A clinical thermometer can show only up to 42 °C, while boiling water is at about 100 °C. The liquid inside would expand far beyond the scale, and the thermometer could break. A laboratory thermometer should be used instead.
Why is a laboratory thermometer not used to measure body temperature?
Its range is too wide and its scale is not marked finely enough near body temperature. Also, it has no kink, so the reading starts falling as soon as it is taken out of the mouth, and the correct temperature cannot be read.
Why are digital thermometers preferred over mercury thermometers?
Mercury is a poisonous substance. If a mercury thermometer breaks, the mercury is difficult to clean up and harmful to people and the environment. Digital thermometers contain no mercury, show the reading directly as numbers and are easier to read.

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