Heat and Temperature | Term 2 Unit 1 | 7th Science - Thermometer | 7th Science : Term 2 Unit 1 : Heat and Temperature
Chapter: 7th Science : Term 2 Unit 1 : Heat and Temperature
Thermometer
Thermometer:
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.
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