(1) Where P (watts) is the radiated power from a body of area A (m2) at temperature T (K). Îµ is emissivity, a dimensionless number between 0 and 1 that determines the. efficiency of a body to radiate and absorb energy. A perfect radiator and absorber has an emissivity of 1. Soil, ice, rock, asphalt and human skin have emissivities slightly less than 1. Ï -8is the Stefan-Boltzmann constant, 5.67 x10 Wm-2T-4 T is the body temperature in Kelvin. So if absolute temperature (in Kelvin degrees) doubles, radiated power increases by a factor of sixteen. Also, changes in temperature alter radiation peak wavelengths. Temperature increases move peak radiation to smaller wavelengths and vice-versa. Equilibrium and Solid Angles
Martin Luther King was often seen wearing a gold Rolex DayDate at many of his speaking functions. Musician John Mayer is seen here wearing his Rolex Daytona. Talk show host Ellen DeGeneres also wears a Rolex Daytona. Actor Brad Pitt is often seen wearing a Rolex Explorer.
President Obama wearing a Jorg Gray 6500 Chronograph. This watch was presented to President Obama by his Secret Service detail on August 2007, and the president has worn it almost exclusively ever since. It retailed for $210 at the Secret Service employee store, has a Japanese Miyota movement and is made in China.