The term convection refers to heat transfer through which of the following?

• A. Liquid and gases
• B. Metal objects
• C. Solid materials
• D. Vacuum spaces

Answer: (A)

Convection is a specific mode of heat transfer that occurs primarily in liquids and gases. This process relies on the movement of the fluid itself; as it is heated, it becomes less dense and rises, while cooler, denser parts of the liquid or gas sink. This continuous cycle creates a convection current that facilitates the distribution of heat throughout the substance.

In contrast, heat transfer through metal objects typically occurs via conduction, where heat is transmitted directly through material without any movement of the medium itself. Solid materials also primarily conduct heat, and vacuum spaces do not conduct heat at all because there are no particles to transfer energy through. Thus, the nature of convection distinctly pertains to the thermal dynamics observed in fluids, which is why the option referring to liquids and gases is the correct answer for this question.