Colourful convection currents

Articles Required: Three tablets of water colours, hard-glass jar.

When you heat water, only a part of it comes into a direct contact with its container which is being heated. But strangely enough, the tempera­ture of entire body of water rises uniformly. So, it means that the heat absorbed by the container spreads equally throughout the entire liquid. The most interesting fact about it is that this process of heating is not haphazard and takes place in a very systematic manner. You can witness it through the experiment explained below:

Fill three-fourths of glass jar with water. Drop small pieces of water-colour tablets into it. Now you'll notice that as this water gets heated, coloured currents emerge from the tablet pieces and come down almost touching the container walls in the form of a foun­tain. Do you know why it happens like this? As the water at the bot­tom gets heated, it becomes lighter and rises upwards. It makes a place for itself at the top displacing the water present there. The water at the top is cool and thus heavy. As a result, it sinks down and fills the gap left by the hot water. This process goes on like this.The particles of colour tablets (red, blue and green) that you have dropped into the water, become a part of the water current after dis-olving in it. They form a definite pattern with the convection currents and you can notice a pretty colour­ful fountain inside the glass jar.