Heat treatment is common in processing semiconductor materials. A 200- mm-diameter silicon wafer with thickness of 725 ?m is being heat treated in a vacuum chamber by infrared heater. The surrounding walls of the chamber have a uniform temperature of 310 K. The infrared heater provides an incident radiation flux of 200k W/m2 on the upper surface of the wafer, and the emissivity and absorptivity of the wafer surface are 0.70. Using a pyrometer the lower surface temperature of the wafer is measured to be 1000 K. Assuming there is not radiation exchange between the lower surface of water and surroundings, determine the upper surface temperature of the wafer. Pyrometer is a non-contacting device that intercept and measures thermal radiation. The device is used to determine the temperature of an object's surface.