If heat is transferred by convection, what is happening?

• A. Direct contact between objects.
• B. Fluids moving heat due to density differences.
• C. Electromagnetic waves carrying energy through space.
• D. No transfer of energy.

Answer: (B)

Convection happens when a fluid moves and carries heat because of density differences. When part of the fluid is heated, it becomes less dense and rises, while cooler, denser portions sink. This sets up a circulating flow that transfers thermal energy from warmer areas to cooler ones. For example, in boiling water, the hotter, less dense water at the bottom rises while cooler water sinks, creating a loop that moves heat through the liquid. This is different from conduction, which requires direct contact for energy transfer, and from radiation, which can move energy through space without a medium. So, heat transfer by convection is the movement of fluids driven by density differences that carries energy with the moving fluid.