Halliday, Resnick & Walker — Temperature, Heat, and the First Law of Thermodynamics: Problem 108

BIO Thermal emission from forehead. Noncontact thermometers (Fig. 18.40) are used to quickly measure the temperature of a person, to monitor for fever from an infection. They measure the power of the radiation from a surface, usually the forehead, in the infrared range, which is just outside the visible light range. Skin has an emissivity \(\epsilon = 0.97\). What is the total power (infrared and visible) of the radiation per unit area when the temperature is (a) 97.0°F (a common early morning temperature), (b) 99.0°F (a common late afternoon temperature), and (c) 103°F (a temperature indicating infection)?