Question

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

Answer 1

A clinical thermometer has a kink that prevents immediate backflow of the mercury from the tube to the bulb, thus allowing us to read the temperature conveniently. This is the reason why we give a jerk to the thermometer before taking a new reading. The jerk positions the mercury below the kink into the bulb.