In class, we saw how steady-state heat flow can be modeled using dc circuit principles. consider a 50 ohm power resistor used as a "dummy load" for a high power radio transmitter. the resistor absorbs 150 watts of power. to shed heat, a heat sink is fastened to the resistor’s housing. the thermal path is depicted below. (not to scale) the contact area between the resistor case and the heat sink is 5 cm by 20 cm. the resistor case is 5 mm thick and made of aluminum. between the resistor and the heat sink sits a copper plate 1 mm thick with the same dimensions as the contact area. assuming thermal conductivities for the copper and aluminum of 400 w/(m-k) and 237 w/(m-k) respectively, compute the thermal resistance in k/watt that the heat sink needs to have to keep the resistor temperature at 80 °c when the ambient temperature is 20°c. hint : draw the equivalent circuit