Parallel beam of light of wavelength 420 nm is focused on a screen at a distance of 50 cm from the lens. What would be the radius of the central bright spot formed? Diameter of the lens is 10 cm.

Explanation

To find the radius of the central bright spot formed by a parallel beam of light focused by a lens, we can use the formula for the radius of the central maximum in diffraction due to a circular aperture:

\[ R = \frac{1.22 \lambda D}{d} \]

Where:
- \( R \) is the radius of the central bright spot,
- \( \lambda \) is the wavelength of light,
- \( D \) is the distance from the lens to the screen,
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