The absorption coefficient of an open window is:

Which of the following statements is true for a perfectly black body?

Infrared radiation is detected by

The surface of a thermos flask is kept shiny because:

If the absorptance and reflectance of a surface are $0.4$ and $0.6$ respectively,then:

If between wavelength $\lambda$ and $\lambda + d\lambda$,$e_\lambda$ and $a_\lambda$ are the emissive and absorptive powers of a body,respectively,and $E_\lambda$ is the emissive power of a perfectly black body,then according to Kirchhoff's law,which of the following is true?