Question

Light with an average flux of $10{\text{W cm}}^{-2}$ falls on a non-reflecting surface at normal incidence having surface area $40{\text{cm}}^2$. The energy received by the surface during time span of $2$ minutes is

• A. $24\text{kJ}$
• B. $240\text{J}$
• C. $12\text{kJ}$
• D. $48\text{kJ}$

Answer 1

The correct option is D $48\text{kJ}$

$E=IAt$
$E=10\times {10}^4\times 40\times {10}^{-4}\times 120$
$E=48000\text{J}$
$E=48\text{kJ}$