Types of Thermometer

There are several types of thermometer, here, I explain only a few of the possibly many types of thermometer.

Mercury thermometer

1. The physical quantity that is used to determine the temperature of a body by means of a mercury thermometer is the length of the thread mercury, or to be more exact, the volume of mercury.

2. When the temperature increases, the volume of the mercury increases too.

3. The sensitivity of a mercury thermometer can be increased by

a. reducing the diameter of the capillary tube.
b. increasing the size of the bulb.
c. using a thinner-walled glass bulb.

4. Normally mercury is used in a thermometer because it:

a. Expands uniformly.
b. has a higher boiling limit.
c. is opaque and therefore it is easier to read off the temperature.
d. is a good conductor of heat.
e. does not stick to the glass.

5. One weakness of the mercury thermometer in the measurement of an accurate temperature is that the glass of the capillary tube also expands when the temperature expands.

In addition to that, it is extremely dangerous if the glass tube breaks because mercury is very poisonous.

Mercury thermometer is suitable to measure temperature between -30 degree celsius to 300 degree celcius.

Resistance thermometer

1. Thermometers which use liquids inside the glass are not suitable to be used for measuring a wide range of temperature. e.g temperature ranging from -250 degree celcius to about 700 degree celsius.

2. A suitable thermometer which is used for the above range of temperatures is a resistance thermometer.

3. A resistance thermometer uses the property of the change in the platinum wire with a change in temperature.

4. The current flowing in the wire experiences more resistance when the wire becomes hot.

5. The change in the resistance of the wire is directly proportional to the change in temperature.

6. A milliammeter can and should be calibrated before hand to measure the temperature.

7. Its calibration of the melting limit of water and the boiling point of water at a pressure of 1 atmosphere is able to convert the milliameter scale to a temperature scale in degree celsius.

8. Therefore, this thermometer is very accurate.


Thermocouple thermometer

1. An electromotive force (e.m.f) will be produced in a thermocouple when there is a temperature difference between the hot junction and the cold junction. Once this happens, a current will flow.

2. This thermometer is very sensitive and responds towards slight change in temperature.

3. Since the physical quantity which is used to measure the temperature is the e.m.f, this thermometer can be connected to other electrical circuits to control or record the surrounding temperature.

4. A thermocouple thermometer is a very sensitive thermometer which is suitable for measuring temperatures ranging from -250 degree celsius to 1600 degree celsius.