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Grade Upto college level Engineering Entrance Exams

The best ideal black body is (a) Lamp of charcoal heated to high temperature (b) Metal coated with a black dye (c) Glass surface coated with coalter (d) Hollow enclosure blackened inside and having a small hole

Profile image of sumit kumar
12 Years agoGrade Upto college level
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2 Answers

Profile image of Saurabh Koranglekar
6 Years ago
Hollow enclosure blackened inside and having a small hole is a very good example of a black body.
Suppose once light enters inside it.
It may be absorbed or it may be reflected.
Since it is blackened from inside, there is a high probability that it will be absorbed.
Now if it is reflected, it will suffer multiple reflections and it is very unlikely that it will come out of the hole because the aperture of hole is too small. Moreover, with each reflection, more and more fraction of it will be absorbed. So, it will serve as a good black body.
Profile image of Vikas TU
6 Years ago
Real materials emit energy at a fraction—called the emissivity—of black-body energy levels. By definition, a black body in thermal equilibrium has an emissivity of ε = 1. A source with lower emissivity independent of frequency often is referred to as a gray body.

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