Question

An electromagnetic wave of intensity $1400\mathrm{W}/{\mathrm{m}}^2$ falls on a metal surface on an area $1.5{\mathrm{m}}^2$ and is completely absorbed by it. Find the force exerted by the beam.

Answer 1

Step 1: Given information

The electromagnetic wave of intensity, $\mathrm{I}=1400\mathrm{W}/{\mathrm{m}}^2$

Area, $\mathrm{A}=1.5{\mathrm{m}}^2$

Step 2: To find

The force exerted by the beam.

Step 3: Calculating force

We know the formula for force, when wave is completely absorbed

$\mathrm{F}=\frac{\mathrm{IA}}{\mathrm{C}}$

By substituting the values, we get

$$\begin{gathered} =\frac{1400\times 1.5}{3\times {10}^8} \\ =7\times {10}^{-6}\mathrm{N} \end{gathered}$$

Therefore, the force exerted by the beam is $7\times {10}^{-6}\mathrm{N}$.