Peoples Physics Concepts

http://www.ck12.org Chapter 16. Light

Example 1

A typical experimental setup for an interference experiment will look something like this:

Recall: for constructive interference we require a path difference ofmλ=dsinθ

d = spacing of slits

m = number of maximum (i.e. m = 0 is the central maximum, m = 1 is the 1st maximum and thus the first dot to the right and left of the center, etc.)

L = distance form diffraction grating to screen

∆y=distance from nth spot out from the center (if m = 1 then it is the 1st spot)

Definitions:

Maximum= place where waves constructively interfere

Minimum= place where waves destructively interfere

Because the screen distanceLis much larger than the slit distanced, one can see that

∆y

L =tanθ≈sinθ.

Thus, the condition for a first maximum becomes

λ=dsinθ=d∆Ly

One can now easily calculate where the first maximum should appear if given the wavelength of the laser light, the

distance to the screen and the distance between slits.

First Maximum:∆y=Ldλ

Example 2

White light (which is comprised of all wavelengths and thus all colors) separates into a rainbow pattern as shown

below.