What is the phenomenon of convection in relation to heat?

Convection refers specifically to the movement of heat through fluids (liquids and gases) caused by temperature differences within those fluids. In this context, when a fluid is heated, it becomes less dense and rises, while cooler, denser fluid descends to take its place. This movement creates a convection current, effectively distributing heat throughout the fluid.

In practical terms, when air is heated—such as by a fire—the warmer air rises, creating a circulation pattern. This is why in a room heated by a radiator, for example, you may feel warm air rising near the radiator and cooler air near the floor. Thus, option B accurately describes convection as the rise of heat due to temperature differences, capturing the essence of how heat moves within fluids.

The other choices do not represent convection accurately. The movement of heat from cold to hot substances characterizes the direction of heat transfer rather than convection itself. The transfer of heat through direct contact describes conduction, which is a different process. Lastly, the notion of heat accumulating in a single place does not capture movement or circulation, which is central to convection's definition.