Convection is

• A. Heat transfer through a solid.
• B. Heat transfer through a fluid that creates currents as warm fluid rises.
• C. Heat transfer by electromagnetic waves.
• D. Heat transfer by direct contact between solids.

Answer: (B)

Convection is the transfer of heat by the movement of a fluid caused by density differences when it is heated. When part of the fluid warms up, it becomes less dense and rises, while cooler, denser portions sink, creating a circulating current that carries thermal energy with the moving fluid. This explains why warm air rises and circulates when room temperatures change, or why boiling water develops upward warm currents. It’s different from conduction, which transfers heat through direct contact in solids or stationary fluids, and from radiation, which is heat transfer by electromagnetic waves that don’t require a medium. So the described idea—heat transfer through a fluid that creates currents as warm fluid rises—fits convection precisely.