A planar source emits a parallel beam of light of power 20 W.Wavelength of light is 600 nm and is incident on a perfectly absorbing surface. Find the number of photons absorbed by the surface per second and the total force exerted on the surface .

Explanation

To solve the problem step by step, we will first calculate the number of photons absorbed by the surface per second and then find the total force exerted on the surface.

### Step 1: Calculate the Energy of a Single Photon
The energy \( E \) of a single photon can be calculated using the formula:
\[ E = \frac{hc}{\lambda} \]
Where:
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