Heat is a form of energy that gets transferred by various methods such as conduction, convection and radiation. In liquids, the heat transfer takes place by convection. Let's look at a simple activity to observe convection in action!
You need two glasses, some colour, hot and cold water. Take hot water in a glass and add some colour to it. Take cold water in another glass and place the CD on this glass as a lid. Now carefully invert the cold glass on the glass containing hot water with colour. The hole in the CD allows hot water to rise up as seen by the movement of coloured water.
Hot water is less dense than cold water and thus rises up in the fluid also transferring the heat with it. This form of heat transfer, called convection, happens in all fluids (liquid and gases) and is due to the actual motion of fluid particles.
If you invert the position of glasses, that is the lower glass contains cold water, and the top glass contains hot coloured water. You will notice that the colours do not mix as the coloured hot water is less dense than cold water and does not sink in cold water (move downwards).
This experiment demonstrates convection as a mode of heat transfer in fluids and also shows how convection only takes place in upwards direction.
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Presented By: Vidya Salehittal, Muktangan English Medium School and Jr. College, Pune
Produced by: IISER Pune Science Activity Center
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