In a thermometer, when the liquid gets heated, it expands, and when it is cooled down, it contracts. It is used to measure temperature.

In this exercise, an activity is explained to understand how the thermometer measures the temperature.
Materials Required:
  • A small glass bottle
  • A rubber cork
  • An empty refill
  • Water
  • Colour
  • Candle
  • Fork
  • Paper
  • Take a small glass bottle.
  • Fill it with coloured water.
  • Make a hole at the centre of the rubber cork.
  • Pass empty refill from the hole of the rubber cork.
Glass bottle with coloured water
  • Make the bottle airtight and observe the water raised in the refill.
  • Make a scale on paper, place it behind the refill and note down the position of the water's surface
  • Hold the bottle with a fork and supply heat to it with the candle. Then observe.
Experimental setup to measure the temperature
What will happen?
  • Initially, the bottle and liquid in the refill are at different temperatures. So, the liquid acquires heat energy from the bottle and starts to rise in the refill. This process continues until they both reach the same temperature (Thermal Equilibrium).
Heat flow
  • Now, heating up the bottle causes an increase in temperature, which creates the difference in temperature between liquid and bottle. So, to attain the thermal equilibrium, the heat transfer takes place between bottle and liquid. This heat transfer enables the expansion in liquid, which is directly related to a change in temperature. So, we can compare this expansion of the liquid in the refill with the temperature.
Heat transfer energy
  • When you cool the bottle, the liquid returns to its original position due to contraction.