Which of the following is an example of heat transfer by convection?

• A. Removal of heat from an engine cylinder by air flowing over its surface.
• B. The heating of the Earth's surface by heat transmitted through space from the sun.
• C. The uniform heating of the air in a room by a floor heater. The heated air rises and forces the cooler air down so it can be heated by conduction.
• D. Heat transfer by radiation from the Sun.

Answer: (C)

Convection is heat transfer through the movement of a fluid. In the room scenario, the floor heater warms the air right at the floor. That heated air becomes less dense and rises, while cooler air moves in to take its place. This creates a continuous circulation known as a convection current, which transports heat through the room. It’s a clear example because you can see the actual movement of the air carrying heat from the floor upward, rather than heat moving only by contact or radiation.

The other options involve different mechanisms: heat reaching the Earth’s surface from the Sun through space is radiation, and heat transfer from the Sun by radiation is also radiation. The first option describes heat transfer to moving air (which is a form of convection as well), but the floor-heater scenario most clearly illustrates the buoyancy-driven air movement that characterizes convection in a room.