An electric heater is used to keep the water in an aquarium warm. To ensure that all of the water is heated as efficiently and evenly as possible, where should the heater be placed?
near the surface of the water
near the bottom of the tank
on the side wall near the top
floating in the upper half
73 exam-style questions on CIE IGCSE Physics 2.3.2 Convection. Each one has a worked solution and a mark scheme showing where the marks go.