Answer:
When a light wave goes through a slit, it is diffracted, which means the slit opening acts as a new source of waves. How much a light wave diffracts<em> (how much it fans out)</em> depends on the wavelength of the incident light. The wavelength must be larger than the width of the slit for the maximum diffraction. Thus, for a given slit, red light, because it has a longer wavelength, diffracts more than the blue light.
The corresponding relation for diffraction is
,
where is the wavelength of light,
is the slit width, and
is the diffraction angle.
From this relation we clearly see that the diffraction angle is directly proportional to the wavelength
of light—longer the wavelength larger the diffraction angle.