Photons of wavelength `lamda=662` nm are incident normally on a perfectly reflecting screen. Calculate their number of photons per second falling on the screen such that the exerted force is 1 N.

Explanation

To solve the problem of calculating the number of photons per second falling on a perfectly reflecting screen that exerts a force of 1 N, we can follow these steps:

### Step 1: Understand the relationship between force and momentum
The force exerted by the photons on the screen is related to the change in momentum. When photons strike a perfectly reflecting surface, they reverse their momentum. The change in momentum (Δp) for one photon is given by:
\[ \Delta p = p_{\text{final}} - p_{\text{initial}} = -p + p = 2p \]
where \( p \) is the momentum of a single photon.
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