Interactive Tutorial about Diffraction
Interactive example : Interference by two slits

Basic examples
Single atom
Pair of atoms
Row of atoms

Interactive examples
1D crystal builder
Polygons of atoms
Different atoms
Ewald sphere
Bragg's law


This example simulates the interference between two waves scattered by two slits. The incoming wave is a plane wave whose wave vector stands normal to the grid formed by the two slits.

The controls on the right allow you to enter the initial wave length, the phase of the initial wave, distance between the slits and the angle under which the diffracted waves should be displayed.

The program will display an image representing the wave vectors drawn in blue and red respectively. The amplitude of each wave is plotted as a sinusoidal wave along each wave vector. The superposition of the two diffracted waves is shown as green wave.

Start exploring and try to answer the questions below: Initially, keep the phase of the incoming wave at 0.5*lambda = 180 degrees = 3.14 radian. Also, for your first trials you should keep all parameters at their default values and just change the angle.

  • How does the amplitude of the green wave change with the angle alpha?

  • What influence does the distance between the two slits have on the diffracted(=green) wave ?

  • What influence does the wave length have on the diffracted(=green) wave ?

  • Under which conditions do you get the highest (lowest) amplitude of the diffracted(=green) wave ?

  • How high is the highest (lowest) amplitude of the diffracted(=green) wave ?

Once you are done, click here to verify your answers.
© Th. Proffen and R.B. Neder, 2003