1. Jan 10, 2008

in thermal radiations what is the difference between effective surface area and surface area of emitting body ,and how to calculate effective surface area of ang body????????

2. Jan 11, 2008

### CraigD

What is the context of the question? You can assume that the MBR has an effective surface area of the entire universe, but that the surface area of the emitting body would be the size of the universe when the radiation was first released.

3. Jan 11, 2008

consider a case of a hollow cylinder with one side open to outside &
external area is covered by insulating material, temperature is T
assuming perfect BB how to calculate heat lost by it in 1 sec,

E=$$\sigma$$*T$$^{4}$$*?

length is l, radius is r.

as i think ?=$$\pi$$*r$$^{2}$$

4. Jan 11, 2008