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 :
(1) ``10×10^3`` J
(2) ``12×10^3`` J
(3) ``24×10^3`` J
(4) ``48×10^3`` J