The diameter and surface emissivity of an electrically heated plate are d = 300 mm and ε = 0.80, respectively. (a) estimate the power needed to maintain a surface temperature of 200°c in a room for which the air and the walls are at 25°c. the coefficient characterizing heat transfer by natural convection depends on the surface temperature and, in units of w/m2.k, may be approximated by an expression of the form h=0.80(ts - too)1/3. (b) assess the effect of surface temperature on the power requirement, as well as on the relative contributions of convection and radiation to heat transfer from the surface.