Question

State the similarities and dissimilarities between the laboratory thermometer and the clinical thermometer.

Answer 1

Hint: Thermometers are the universal instruments of measuring temperatures of objects. There are different types of thermometers based upon their purpose and the objects whose temperatures they are used to measure. Two thermometers differentiated according to this classification are the laboratory thermometer and the clinical thermometer.

Complete answer:
Thermometers are measuring instruments used to measure the temperature of an object. They can be classified based upon their purpose of use, that is, the kind of objects whose temperature they are used to measure.
Two types of thermometer based upon this classification are the laboratory thermometer or ‘lab’ thermometer in short and the clinical thermometer.
The lab thermometer is used to measure temperatures other than the human body in laboratory experiments whereas the clinical thermometer is used to measure the temperature of the human body.
The similarities between clinical and lab thermometers are –
1) Their structure is essentially a long glass tube with a bulb at the end.
2) There is mercury present in the bulb for both thermometers.
3) Usually both of them are calibrated according to the Celsius scale.
The dissimilarities between clinical and lab thermometers are –
1) For clinical thermometer, the temperature range is ${{35}^{0}}C-{{42}^{0}}C$ (the normal human body temperature is ${{37}^{0}}C$) while for the lab thermometer the temperature range is from $-{{10}^{0}}C\text{ to }{{110}^{0}}C$.
2)The lab thermometer is used to measure the temperatures of objects other than the human body, and usually in lab experiments whereas the clinical thermometer is used to measure the temperature of the human body for clinical purposes.
3) The clinical thermometer has a kind of kink at the bulb that does not allow the back flow of mercury whereas the lab thermometer has no such kink in it.

Note:
Students must be thinking that if lab thermometers cover the range of the human body temperature then why were clinical thermometers developed separately and are being used for this purpose. The reason is that even though the lab thermometer covers the range of the human body temperature, the calibrations are such that it will be very difficult to measure the minute temperature changes in the human body on the lab thermometer. The clinical thermometer is graduated specifically for this purpose and hence, it is much easier to read the changes in the human body temperature using this thermometer.