Physics

Problem

A body is in thermal equilibrium with its surroundings. Which relation between its absorptive power

a_{\lambda}

and emissivity

\varepsilon_{\lambda}

at a given wavelength

\lambda

is valid? a)

a_{\lambda}+\varepsilon_{\lambda}=1

a_{\lambda}=\varepsilon_{\lambda}

a_{\lambda}\,\varepsilon_{\lambda}=1

a_{\lambda}>\varepsilon_{\lambda}\;\text{for all }\lambda