Thermometer is the most common instrument to measure temperature.
There are various kinds of thermometers. Some of them are like glass tubes which look thin and are filled with some kind of liquid.
Why Mercury or Alcohol is used in Thermometer?
Mostly Alcohol and Mercury are used in thermometers as they remain in liquid form even with a change of temperature in them. A small change in the temperature causes change in volume of a liquid. We measure this temperature by measuring expansion of a liquid in thermometer.
Properties of Mercury:-
* Its expansion is uniform. (For equal amounts of heat it expands by equal lengths.)
* It is opaque and shining.
* It does not stick to the sides of the glass tube.
* It is a good conductor of heat.
* It has a high boiling point (357°C) and a low freezing point (−39°C). Hence a wide range of temperatures can be measured using a mercury thermometer
Properties of Alcohol
* The freezing point of alcohol is less than −100°C. So it can be used to measure very low temperatures.
* Its expansion per degree Celsius rise in temperature is very large.
* It can be coloured brightly and hence is easily visible.