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### Diffraction

• Diffraction is the bending of waves around obstacles.
• Huygen’s Principle: Every point on a wave front acts as a source of wavelets that move forward at the wave speed; the wave front at a latter time is the surface tangent to the wavelets.
• Diffraction of light from a narrow slit: If the screen is far away, the first dark fringe occurs for an angle theta given by

Sin (theta) = lambda / W

where lambda is the wavelength of light, W is the width of the slit, and theta is the angle that the line from the center of the slit to the dark fringe makes with the line from the center of the slit to the central maximum.

• In general dark fringes occur at angles theta given by

Sin(theta) = m * lambda / W

where m = 1, 2, 3,… The bright fringes are situated halfway between the dark ones.

## Diffraction

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