black body radiation problem

How is it stated, that a mirror can absorb/emit electro-magnetic radiation?

it reflect the EM radiations which is incident on it same

A black body absorbs all incident electromagnetic radiation on it, irrespective of the frequency or the angle of incidence. At thermal equilibrium, it also emits a radiation known as 'black body radiation'.

Now, assuming you are talking about a glass mirror, it doesn't absorb any radiation. It 'reflects' light. Light is but a tiny fraction of the spectrum of electromagnetic radiation, and only that is reflected. Frequencies outside the visible light spectrum just pass through a mirror. So, how can a mirror and a black body be compared at all?

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actually there is a lot of difference between a black body and a mirror.

Black body : absorbs radiation completely.

mirror: it is a completely reflective body, and does not absorb any energy or radiation.

mirror

robo_warriorif a black body absorbs and emits all the electromagnetic radiation then what is the diff b/w a black body and a mirror(i think it also does the same).

mirror doesn't absorb radiation it reflect all of radiation..and black body absorbs all of radiation that is ideal case and not possible in practical life...

robo_warriorif a black body absorbs and emits all the electromagnetic radiation then what is the diff b/w a black body and a mirror(i think it also does the same).

The error is in that part of the definition,'...emits all the electromagnetic radiation...'
An ideal black body radiates energy in the frequency defined by the Planck Law.
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However it will absorb all frequencies incident on it. It is a different matter that such absorption may raise the temperature of the black body making it re radiate energy . However this re radiation will be in a frequency spectrum defined by the Planck law.
A reflector on the other hand just throws back whatever that falls on its surface. A coloured reflector will absorb the complimentary colours to its colour. A red reflector will absorb green frequencies.

DEFINITION OF BLACK BODY IS that it will absorb all incident radiation and then it will give up all the radiations .
In case of mirror only phenomenon of reflection takes place and not absorption.