Question

What is emissivity formula?

Answer 1

1. Emissivity can be defined as the ratio of the emissive power of body temperature and emissive power of the black body at same temperature.
2. It is a dimensionless quantity.
3. The value of emissivity lies between 0 to 1.
4. For ideal black body emissivity is 1.
5. The expression for emissivity
   $$\begin{gathered} \mathrm{e}=\frac{\mathrm{Emissive}\mathrm{power}\mathrm{of}\mathrm{the}\mathrm{body}\mathrm{at}\mathrm{temperature}\mathrm{T}}{\mathrm{Emissive}\mathrm{power}\mathrm{of}\mathrm{a}\mathrm{blackbody}\mathrm{at}\mathrm{same}\mathrm{temperature}\mathrm{T}} \\ \mathrm{e}=\frac{\mathrm{E}}{{\mathrm{E}}_0} \end{gathered}$$