I have come across a problem where I must find the rate of heat flow to the surface of a sphere from the center. The sphere has a constant coefficient of thermal conduction. The problem also supplies the temperature difference between the center/surface and the radius of the sphere. My question is whether it would be correct to simply apply the conduction formula Q/t=kA(T2-T1)/L even though the area of contact between two adjacent surfaces will be changing at different radii. If applying this equation is incorrect, what method should be used for this problem? Will calculus be required due to the varying area of contact? Thank you for your time.