Question

You may have noticed a few sharp jerks are given to a clinical thermometer before using it. Why is it done so?

Answer 1

Hint: Clinical thermometer is also known as Mercury thermometer. This thermometer uses mercury as the metal rising in the glass to measure the temperature. The volume of mercury slightly changes with the temperature.

Complete answer:
It is known to us that mercury is only a metal liquid at room temperature. This property is useful in the rising in the narrow tube of the thermometer. The thermometer has a bulb containing mercury. It is attached to a narrow glass tube.
The volume of mercury in the tun=be is much less than the volume in the bulb. The volume of mercury changes very slightly with the temperature. The small change in volume is a large leap in a narrow tube.
It is calibrated in ice for zero temperature and in water vapor mixture for 100 deg. Temperature.
Bur ass mercury is liquid metal lying in the bulb. There may be difficulty in rising because of being in the bulb for a long time. In that case the movement of the mercury in the tube will not be the same as desired.
Then the jerks are given in order to get the accurate reading. The jerks are helping mercury to allow the mercury level to flow into the bulb, below from the normal temperature.

Note: Thermometers made of different materials might be expected to give different intermediate readings due to different expansion properties. In practical purpose the substances chosen will have a reasonable value of thermal expansion coefficient. Nowadays digital thermometers are used for accuracy more than the mercury thermometers.