Atransistor, which may be approximated as a hemispherical heat source of radius ro 0.1 mm, is embedded in a large silicon substrate (k 125 w/m k) and dissipates heat at a rate q. all boundaries of the silicon are maintained at an ambient temperature of t 27 c, except for the top surface, which is well insulated.
obtain a general expression for the substrate tempera ture distribution and evaluate the surface temperature of the heat source for q = 4 w