Consider a power transistor encapsulated in an aluminum case that is attached at its base to a square aluminum plate of thermal conductivity n 240 w/mk, thickness / 6 mm, and width : 20 mm. the case is joined to the plate by screws that maintain a contact pressure of 1 bar, and the back surface of the plate transfers heat by natural convection and radiation to ambient air and large surroundings at 7 7sur 25c. the surface has an emissivity of 0.9, and the convection coefficient is k 4 w/m2 k. the case is completely enclosed such that heat transfer may be assumed to occur exclusively through the base plate (a) if the air-filled aluminum-to-aluminum interface is characterized by an area of ac x 10 m and a roughness of 10 um, what is the maximum allow- able power dissipation if the surface temperature of the case. to is not to exceed 85°c? (b) the convection coefficient may be increased by subjecting the plate surface to a forced flow of air. explore the effect of increasing the coefficient over the range 4 shs 200 w/m .k.