Question

Light with an average flux of $20{\text{W/cm}}^2$ falls on a non-reflecting surface at normal incidence having area $20{\text{cm}}^2$. The energy recieved by the surface during timespan of $1\text{minute}$ is :

• A. $24\times {10}^3\text{J}$
• B. $48\times {10}^3\text{J}$
• C. $10\times {10}^3\text{J}$
• D. $12\times {10}^3\text{J}$

Answer 1

The correct option is A $24\times {10}^3\text{J}$

Total energy recieved by surface is,
$$E=IAt$$

Where,
$I$ = Intensity
$A$ = Area
$t$ = time interval

$E$ $=$ $\frac{20}{{10}^{-4}}$ x 20 x ${10}^{-}4$ x $60$

$E$ $=$ $24$ x${10}^3$ $J$