Convection is defined as the transfer of heat through the movement of fluids caused by differences in temperature and density.

• A. The transfer of heat through electromagnetic waves.
• B. The transfer of heat through the movement of fluids caused by differences in temperature and density.
• C. The transfer of heat by direct contact.
• D. The transfer of heat by phase changes.

Answer: (B)

Convection is heat transfer through the movement of a fluid caused by differences in temperature and density. When part of the fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks, creating a circulating motion that carries heat with it. This is why you can feel warm air circulating from a heater or see bubbles carry heat upward in boiling water. The statement captures this mechanism exactly. Other ways heat moves are different: radiation transfers energy as electromagnetic waves and can occur without any medium; conduction transfers heat through direct contact, usually through solids, by particle interactions; and phase changes move heat when a substance changes state, via latent heat, not primarily because of fluid movement.