A parallel beam of monochromatic light of wavelength 500nm is incident normally on a perfectly absorbing surface. The power through any cross- section of the beam is 10 W. Find (a) the number of photons absorbed per second by the surface and (b) the force exerted by the light beam on the surface.

Explanation

To solve the problem step by step, we will break it down into two parts: (a) calculating the number of photons absorbed per second and (b) calculating the force exerted by the light beam on the surface.

### Step-by-Step Solution:

**Given:**
- Wavelength of light, \( \lambda = 500 \, \text{nm} = 500 \times 10^{-9} \, \text{m} \)
- Power of the beam, \( P = 10 \, \text{W} \)

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