Waves of equal wavelength and with a constant difference of phases are called coherent waves. When coherent waves superimpose, time-stable interference of intensity minimums and maximums occurs.
This model illustrates the concept of interference on the example of Young's experiment. A beam of light falls on a screen with a small hole on it. The light passes through the hole and reaches a second screen, which contains two slots. Coherent beams coming from each of the two slots interfere when they reach the third screen. The diagram indicates the distance between the slots d (you may change this distance by using the input window), distance between screens L, and well angle θ. The alternating values of this angle, as well as the width of the interference band, are indicated in a small window at the bottom of the screen.
Observe the screen in the model's right-side window to study the impact of interference and intensity of radiation on the distance to the system's optical axis. The color of the diagram corresponds to the wavelength of the beam, which you may modify.
Interference occurs only when several beams fall on the same sport. This is why two slots are present on the second screen. Otherwise, one would need two different sources of light to conduct the experiment.