----- Original Message ----- From: "Trent Shipley" <[EMAIL PROTECTED]> To: "Brin-L" <[EMAIL PROTECTED]> Sent: Monday, November 12, 2001 8:06 PM Subject: Black body radiation
> What is black body radiation? > Well, i'll try to give this quickly. A black body is a body that doesn't reflect any radiation. It absorbs it all. To understand why this is important, let us consider the opposite: a mirrored surface. The radiation on it is perfectly reflected. So, a 0.3 ev photon is just reflected off the surface. 0.3 ev corresponds, roughly, to 3000 deg C (to within rounding you can forget that 0C = 273K...and have C=K). 0.3 ev corresponds to visible light So, the radiation spectrum off a perfect reflector is simply the radiation spectrum incident upon it. But, a black body does not reflect radiation. Instead it absorbs it. A black body does emit radiation, but the radiation is in a spectrum that corresponds to the energy of the body. So, the mean energy of photons off a black body at room temperature is about 0.03 ev ~=300K =27C. Photons of this energy are infrared and are not visible. The temperature of the surface of the sun, on the other hand, is about 3000 C. This means that the mean energy of the photons from the sun is 0.3 ev...which corresponds to yellow light. So, the black body radiation is the radiation of photons that have an energy distribution that is characteristic of the energy of the surface. Dan M.
