Question

An electric heater of surface area $200$ cm${}^2$ emits radiant energy of $60kJ$ at a time interval of $1$ min. If its emissivity be $0.45$, what would be the radiant energy emitted by a black body in one hour, identical to the electrical heater in all respects?

• A. 8000 kJ
• B. 4000 kJ
• C. 2000 kJ
• D. 6000 kJ

Answer 1

The correct option is A 8000 kJ

Energy emitted by a black body in one min $=\frac{60}{0.45}$

Energy emitted by a black body in one hour $=\frac{60}{0.45}\times 60=8000KJ$