Light with an average flux of $20\ W/cm^2$ 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 $12\times10^3\ J$

B $24\times10^3\ J$

C $48\times10^3\ J$

D $10\times10^3\ J$

The answer is B.

Solution

Energy received = intensity × area × time $= 20\ W/cm^2 \times 20\ cm^2 \times 60\ s = 24 \times 10^3$ J

Concept energy from flux, area and time

49 questions from this chapter have appeared across 24 exam years.