Light with an average flux of 20 W/cm² falls on a non-reflecting surface at normal incidence having a surface

Question

Light with an average flux of 20 W/cm² falls on a non-reflecting surface at normal incidence having a surface area of 20 cm². The energy received by the surface during a time span of 1 minute is:

Accepted Answer

1.  **Given Data:**
    *   Average Flux (Intensity), $I = 20 	ext{ W/cm}^2$.
    *   Surface Area, $A = 20 	ext{ cm}^2$.
    *   Time, $t = 1 	ext{ minute} = 60 	ext{ s}$.
2.  **Concept:** The energy ($U$) received by a surface is the product of power ($P$) and time ($t$). Power is the product of intensity ($I$) and area ($A$).
    *   $P = I 	imes A$
    *   $U = P 	imes t = I 	imes A 	imes t$
3.  **Calculation:**
    *   $U = (20 	ext{ W/cm}^2) 	imes (20 	ext{ cm}^2) 	imes (60 	ext{ s})$
    *   $U = 400 	ext{ W} 	imes 60 	ext{ s}$
    *   $U = 24000 	ext{ J} = 24 	imes 10^3 	ext{ J}$.

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