Is the steady-state condition for the conductor a fixed ##\Delta T##? In other words, must the surrounding media at temperatures ##T_1## and ##T_2## be approximate heat sinks?
Okay, yes. I was thinking that something must be idealized. Why must heat exchange from the side material be minimized though? Doesn't that just lead to a change in ##\Delta T## and thus a time dependent ##\dot{Q}##? In other words, in that case we may rewrite the equation to say something like...
I recently read in a Khan Academy article that the rate of energy exchange through heat across a material of thickness ##d##, surface area ##A##, and thermal conductivity ##k## can be approximated by $$\dot{Q} = \frac{kA\Delta T}{d}$$ where ##\dot{Q}## is the heat rate and ##\Delta T## the...