The double slit experiment is a great example of wave interference. This experiment is also quite famous for other reasons and we will return to it in later parts of the class. The set-up is simple (see figure below). We shine light on a screen with two holes (two slits) of a certain size and a certain distance apart. If the holes are very small compared to the wavelength of the incident light, then it is just as if we had two point sources separated by a small distance. Light will go through those holes and the waves will travel out in all directions.This is a very clean set-up and we can easily predict the interference pattern of the light if we put a screen in the way (the grey bar in the picture below). The light on the screen will look like a long line of equally spaced dark and bright spots (this picture on the screen is shown on the right below). At the bright spots the waves from each slit are reinforcing each other. The dark spots are where the two waves completely cancel.
And this is the demo for the double slit: