Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

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:

12 × 10³ J

24 × 10³ J

48 × 10³ J

10 × 10³ J

Step-by-Step Solution

Given Data: Average Flux (Intensity), $I = 20 \text{ W/cm}^2$ . Surface Area, $A = 20 \text{ cm}^2$ .

Time, $t = 1 \text{ minute} = 60 \text{ s}$ .

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 ( $A$ ). $P = I \times A$ $U = P \times t = I \times A \times t$
Calculation: $U = (20 \text{ W/cm}^2) \times (20 \text{ cm}^2) \times (60 \text{ s})$ $U = 400 \text{ W} \times 60 \text{ s}$

$U = 24000 \text{ J} = 24 \times 10^3 \text{ J}$ .

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