Question

Two test tubes full of water are heated-one from below and the other near the top. In which case will the water heat up faster and why?

Answer 1

The test tube which is heated from below will heat up faster. When we heat water from below, the molecules at the bottom of the water start heating and expanding due to which they become light and move upwards. On moving upwards, they transfer the heat energy to other molecules. After transferring their energy, they contract and return to the bottom again. This cycle continues till the entire water gets heated through the convection mode. If water is heated from above, the heated molecules at the top will change their state to form steam, as they can hardly transfer the heat energy to the bottom layer due to the convection currents.