Question

What happens to convection currents when the liquid or gas is no longer heated?

Answer 1

they stops and the whole liquid or gas comes to a final equal temprature..

Answer 2

The currents are produced by applying heat, most often to the bottom. The warmed fluid is 'lighter' than the cold fluid surrounding so it rises to allow colder fluid to replace it and be heated. As soon as the heat is removed, all the fluid rapidly comes to a single temperature and convevtion does not happen! An opposite effect happens when cold air sits on the surface of a lake. In this case the water at the surface cools, gets 'heavier' and sinks. In this case the convection currents operates downwards.