Question

What is a clinical thermometer? State its special features. Draw a labelled neat diagram of a clinical thermometer showing the range of temperature marked on it.

Answer 1

Hint: Thermometer is a device used to measure the temperature. The thermometer used by doctors to measure the temperature of patients has a reading range which is different from the range of a normal thermometer. This is because the purpose of such a thermometer is only to measure the body temperature.

Complete step by step solution:
Thermometer is an instrument which is used to measure temperature. It consists of a glass tube which is sealed at both ends. Usually the glass tube is filled with mercury. If we place the thermometer on a hot object the bulb of the thermometer gets heated up this results in the heating of the liquid inside the glass tube. We know that mercury is a liquid metal. When heat is provided it will expand. So, the level of mercury in the glass tube will rise which gives us the measurement of the temperature of the hot object.

Similarly, when the temperature falls the liquid will contract resulting in the lowering of the level of mercury in the glass tube. The temperature is found by noting the reading on the temperature scale corresponding to the level of the liquid in the tube. A normal thermometer will have readings on the scale from zero degree Celsius to hundred degree Celsius.

The thermometer used by doctors is different from the normal thermometer. The thermometer that is specially made for measuring the body temperature is called a clinical thermometer. The difference between this thermometer and the normal thermometer is that the readings on the clinical thermometer starts from 35 degree Celsius to 42 degree Celsius.

There is a slight bend in the stem above the bulb, this bend is called the constriction. It is this constriction that prevents the mercury from falling back. The normal temperature of a healthy person is 37 degree Celsius. This reading is marked by a red Arrow in the thermometer.
The diagram of a clinical thermometer is shown below:

Note: In some thermometers alcohol is also used instead of mercury. Alcohol level will also arise when the temperature increases and fall down when the temperature decreases. Alcohol is colored using red or green so that it can be seen clearly. But since alcohol boils at 80 degree Celsius for higher temperature measurements mercury is used.