Diffraction
Diffraction is the bending of light around a corner. It is a property very specific to the
wave model of light. When light shines through an opening, we easily imagine a very
straight line shadow appearing, however as light passes a corner it bends like waves
and interferes creating a diffraction pattern on a screen rather than a straight line. To
get a pattern as shown above, a light is shone on a small opening to create an image
on a distant screen.
One big assumptions must be made for this description of the single slit diffraction
pattern: that the slit size is small, relative to the wavelength of light.
Math for diffraction problems can be done in 2 ways. One method using an
assumption based on small angles, typically under 10o:
𝑑𝑥
λ=
𝑛𝑙
Or for any angle,
 Wavelength ( λ ) of incoming light is often called monochromatic light due to
the fact the only one specific wavelength is used (mono). (units, m)
 d, is the distance between slits on the diffraction grating, or the width of a
single slit (units, m)
 n is the number of bright points away from the central one on the screen (no
units)
 x is the distance between bright spots on the screen (units, m)
 l is the distance from the grating to the screen (units, m)
You can see the issue, lots of the same units can make it easy to make a mistake.
x
L
For the above example, 2 side by side points are used to measure x, so n=1