Derive the relationship between the pin efficiency when a pin with constant cross$-$sectional area Ac$,$ length p$,$ length $L,$ and thermal

conductivity $k$ is exposed to a medium with a thermal transfer coefficient $h$ that is temperature T$..$ Assume that the temperature at the

tip of the pin is almost as long as T$.$ Ignoring the heat transfer at the tip of the pin, we call the temperature at the bottom of the pin To$.$

Briefly summarize the relationship between $($a$)$ the diameter D of a cylindrical pin with thickness t and $($b$)$ a rectangular pin.