Question

Radiant energy is incident on a body at the rate of 1000 joule/min. The coefficient of emission of body is 0.8 and its coefficient of reflection is 0.1. The radiant energy transmitted by the body in 5 minutes is -

1) 250 J       2) 1000 J      3) 500 J      4) 750 J


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Answer 1

Given : Radiant energy is incident on a body at the rate of 1000 joule/min. The coefficient of emission of body is 0.8 and its coefficient of reflection is 0.1

To find : radiant energy is incident on a body at the rate of 1000 J/min.

so, Total incident energy in 5 min , Q = 1000 J/min × 5 min = 5000 J

we know,

absorbed + reflection + transmission = 1

⇒0.8 + 0.1 + transmission = 1

⇒transmission = 1 - 0.9 = 0.1

The radiant energy transmitted by the body in 5 min = transmission × total radiant energy

= 0.1 × 5000

= 500 J

Therefore option (3) 500 J , is correct choice.