1) A 10-cm long and 20-cm wide circuit board is covered with 100 closely spaced chips, each generating heat at a rate of 0.08 W and transferring it by convection to the surrounding air at 25°C. Heat transfer from the back surface of the board is negligible. What is the average surface temperature of the chips? The convective heat transfer coefficient on the surface of the board is 10 W/(m^2 K) and radiative heat transfer is negligible.
2) Toasters, blow dryers, and electric space heaters do their jobs via electric resistance heating: when electricity flows through a high-resistance wire, the temperature of the wire goes up, and heat is dissipated from the wire to the surroundings. A particular toaster uses 20 feet of a Nichrome resistance wire to cook toast. The diameter of the wire is 0.0285 inches.
a. Estimate the radiant heat transfer from the wire. You can assume that the surface temperature of the wire is approximately 750°C and that the wire is a thermal black body.
b. About how much current will this toaster use when connected to a 110 V power source?