Why is white light separated into a spectrum of colors when it is passed through a diffraction grating?
The diffraction angle (theta) is given by
n x (lambda) = d sine(theta)
where
lambda = wavelength
theta = diffraction angle
d = grating spacing
n = order (1,2,3 etc.)
so each wavelength is diffracted through a slightly different angle. If the incident light is white light then you will see a rainbow at each value of n.
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Due to varying wavelengths, the wave speed of each constituent of the visible light spectrum will vary, and so will the angle at which the light will leave the diffraction grating. - Hope that makes some sense. (-:
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