# Doubt in Fourier's Law of Heat conduction

## Main Question or Discussion Point

Hello friends
Fourier law of heat conduction states that:

Q ~ A.(Dt/Dx) where A= area normal to direction of heat flow.
Dt/Dx= temp gradient in same direction.

Now, obviously rate of heat flow will depend upon temp gradient but my doubt is how/why rate of heat flow is affected by this NORMAL area A ?????

Thnx

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Back in the 1800s they used to think heat was a fluid... called a caloric fluid. The reason they thought this was because it's behaviour was similar to that of a fluid.

Using the ideas of a fluid, in particular lets use water, if we maintain a *constant* pressure gradient on a pipe from one end to another and change its diameter, would you say more water now flows? It's the same idea for heat.

cjl
Hello friends
Fourier law of heat conduction states that:

Q ~ A.(Dt/Dx) where A= area normal to direction of heat flow.
Dt/Dx= temp gradient in same direction.

Now, obviously rate of heat flow will depend upon temp gradient but my doubt is how/why rate of heat flow is affected by this NORMAL area A ?????

Thnx
Because the total heat flow depends on the size of the cross section. Think about it - will a wire conduct as much heat from one point to another as a large rod of the same material?

yeah, I get it now after a bit of thinking. If source of heat is placed at one end then more the area of cross section more the medium is available for flow so more heat will flow. It was simple.
Thnx coto and cj.