Question

Light with an average flux of $20\,\Omega/cm^2$ falls on a non-reflecting surface at normal incidence having surface area $20\,cm^2$. The energy received by the surface during time span of $1\,minute$ is :

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

Answer 1

Answer: (C)

$24 \times 10^3J$

Answer 2

Energy received = Intensity $\times$ Area $\times$ Time
$I=\frac{E}{A}$
$E=IAt$
$=\frac{20}{10^{-4}}\times 20\times 10^{-4}\times 60$
$=24 \times 10^{3}\,J$