one week left for my board exams.... so PLEASE ANSWER In kirchoff's law of heat radiations it has been said that the ratio of spectral emissive power to the spectral absorptive power ( both corresp. to a wavelength ) at same temperature is same for all bodies and is equal to the spectral emissive power of a black body corresp. to same wavelength at that temperature. e / a = E This proves that emissive power absorptive power (at same temp.) But while citing examples, books tell us the example of sodium vapour which when absorbs the light of same wavelength ( when light form some source at higher temperature is allowed to pass through it when cold ) as it would have emitted when excited. and many more examples where the temp. of absorption is not equal to that of emission ... WHY THIS CONDITION STATED IN THE LAW IS NOT OBEYED ??? OR AM I WRONG IN UNDERSTANDING THE LAW ???

one week left for my board exams.... so 

PLEASE ANSWER

 

 

 

In kirchoff's law of heat radiations it has been said that the ratio of spectral emissive power to the spectral absorptive power ( both corresp. to a wavelength  ) at same temperature is same for all bodies and is equal to the spectral emissive power of a black body corresp. to same wavelength  at that temperature.

e / a = E

This proves that emissive power  absorptive power (at same temp.)

But while citing examples, books tell us the example of sodium vapour which when absorbs the light of same wavelength ( when light form some source at higher temperature is allowed to pass through it when cold ) as it would have emitted when excited.

and many more examples where the temp. of absorption is not equal to that of emission... WHY THIS CONDITION STATED IN THE LAW IS NOT OBEYED ???  OR AM I WRONG IN UNDERSTANDING THE LAW ???