Which heat transfer mode involves energy flowing through a medium due to a temperature gradient within the medium?

Which heat transfer mode involves energy flowing through a medium due to a temperature gradient within the medium?

• A. Conduction
• B. Convection
• C. Radiation
• D. Evaporation

Answer: (A)

Conduction is the mode where energy flows through a medium due to a temperature gradient within the medium. In this process, heat is transmitted by interactions between neighboring particles and, in solids, by free electrons. When part of the material is hotter, its particles have more energy and transfer some of that energy to adjacent particles, creating a flow of heat along the temperature gradient. This transfer can happen even if the material as a whole isn’t moving, which distinguishes conduction from convection. A common way to describe it quantitatively is Fourier’s law, where the heat flux is proportional to the negative temperature gradient and scaled by the material’s thermal conductivity. For example, heating one end of a metal rod and allowing the heat to travel to the cooler end illustrates conduction clearly. Convection would require bulk fluid motion to carry heat, not just transfer through interactions in place. Radiation transfers energy via electromagnetic waves and does not require a medium at all. Evaporation involves latent heat associated with a phase change at a liquid surface, not simply energy movement within the medium due to a gradient.

Conduction is the mode where energy flows through a medium due to a temperature gradient within the medium. In this process, heat is transmitted by interactions between neighboring particles and, in solids, by free electrons. When part of the material is hotter, its particles have more energy and transfer some of that energy to adjacent particles, creating a flow of heat along the temperature gradient. This transfer can happen even if the material as a whole isn’t moving, which distinguishes conduction from convection.

A common way to describe it quantitatively is Fourier’s law, where the heat flux is proportional to the negative temperature gradient and scaled by the material’s thermal conductivity. For example, heating one end of a metal rod and allowing the heat to travel to the cooler end illustrates conduction clearly.

Convection would require bulk fluid motion to carry heat, not just transfer through interactions in place. Radiation transfers energy via electromagnetic waves and does not require a medium at all. Evaporation involves latent heat associated with a phase change at a liquid surface, not simply energy movement within the medium due to a gradient.