An electromagnetic wave of intensity 100 W/m² is incident normally on a square black card whose sides are 25 cm.If the card absorbs all of the radiation incident on it,the approximate force exerted by the wave on this card is A)64 nN B)16 nN C)42 nN D)10 nN E)None of these is correct.

Question

Quizplus · Accepted Answer

The force exerted by an electromagnetic wave can be calculated using the formula $F = \frac{I \cdot A}{c}$, where $I$ is the intensity of the wave, $A$ is the area of the surface, and $c$ is the speed of light ($3 \times 10^8 m/s$). Given that the intensity $I = 100 W/m^2$ and the side of the square card is $25 cm = 0.25 m$, the area $A = (0.25 m)^2 = 0.0625 m^2$. Substituting these values into the formula gives $F = \frac{100 W/m^2 \cdot 0.0625 m^2}{3 \times 10^8 m/s} = \frac{6.25}{3 \times 10^8} N$, which calculates to approximately $2.08 \times 10^{-8} N$ or $20.8 nN$, which is not listed among the options provided.

An Electromagnetic Wave of Intensity 100 W/m2 Is Incident Normally

An Electromagnetic Wave of Intensity 100 W/m² Is Incident Normally