Question

A black body of emissive power 81 J/`m^(2)` s when it is at 300 K and ordinary body of emissivity 0.8 when it is at 500 K. what is the emissive power of an ordinary body?
A. 500 J/`m^(2)s`
B. 600 J/`m^(2)` s
C. 800 J/`m^(2)` s
D. 400 J/`m^(2)` s

Answer 1

Correct Answer - A
`(E_(2))/(E_(1))=((T_(2))/(T_(1)))^(4)=((500)/(300))^(4)`
`E_(2)=(625)/(81)xxE_(1)`
`E_(2)=(625)/(81)xx81`
`E_(2)=625`
`E=0.8xx625`
`=500`
`E=500J//m^(2)s`.