Learning Goal: To understand the cause of constructive and destructive interference for the double-slit experiment, and to explain how the interference pattern depends on the parameters of the emitted waves. For this tutorial, use the PhET simulation Wave Interference. This simulation allows you to send waves through a variety of barriers and look at the resulting interference patterns.

In double slit interference experiments it is essential that the waves lurk coherently, that is, that the relative phase of the waves that reaches each slit is maintained over time, this is achieved when point sources are used by passing light through a initial slit and if a laser is used it is already consistent at the output.

When the light passes through the slits, the relative phase between the two rays is due to the optical path difference of each one, when this path difference is equal to a whole number of donut lengths, it has constructive interference and if it is a number sowing we have destructive interference.

d sin θ = m λ constructive

d sin θ = (m + ½) λ destructive

where d is the distance between the two slits, lam is the wavelength and m is an integer called the interference order