Question

A spherical body of area $300{\text{cm}}^2$ has emissive power of $3000{\text{J/m}}^2\text{s}$. Find the amount of thermal energy radiated by the body in $10\text{s}$.

• A. $1000\text{J}$
• B. $5000\text{J}$
• C. $9000\text{J}$
• D. $900\text{J}$

Answer 1

The correct option is D $900\text{J}$

Given,
Area, $A=300{\text{cm}}^2=0.03{\text{m}}^2$
Emissive power, $E=3000{\text{J/m}}^2\text{s}$
Time, $t=10\text{s}$
We know that,
Emissive power, $E=\frac{Q}{At}$
$\Rightarrow Q=EAt$
$\Rightarrow Q=3000\times 0.03\times 10$
$\Rightarrow Q=900\text{J}$