Single Slit Diffraction[br][br]This shows two rays, one from each edge of the slit (or aperture) to show how they interfere when they intersect. [br][br]You can adjust the slit width (a), the distance to the screen, and the position of intersection of the two rays (effectively, the angle of the ray from the normal to the slit)[br][br]It will then calculate the superposition of the two waves: Positive for a peak, negative for a trough, and zero for destructive interference, where the dark nodal lines will be seen. (This used to say "energy", but that is not technically correct. It is simply the superposition, because in 2D, the actual meaning of the wave is confusing!)[br]Check that it's right by looking at the exact position of the sine waves at right angles to the ray.[br][br]This diagram should be used with the formula for calculating the angle of the m-th dark nodes in a single slit diffraction with light of wavelegth [math]\lambda[/math] and slit of width a.[br][math]sin\theta = \frac {m \lambda}{ a} [/math].