Young's double slit produces equally spaced bright and dark fringes

Interference & Diffraction — AQA A-Level Physics

A laser passes through a single slit (to create two coherent sources) and then through a double slit.
The two diffracted beams overlap and interfere on a distant screen.
Bright fringes (maxima) form where constructive interference occurs: path $difference = n \lambda$.
Dark fringes (minima) form where destructive interference occurs: path $difference = (n + 1/2) \lambda$.
With monochromatic light, each bright fringe has the same width and intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared..
The central maximum ($n = 0) has zero path differenceThe difference in distance travelled by two waves from their sources to a given point. Determines whether constructive or destructive interference occurs.$.

White light through a double slit

The central maximum is white (all wavelengths interfere constructively here).
Other maxima show a spectrum: blue/violet nearest the centre (shorter wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m)., less diffraction), red furthest out.
Spectra eventually overlap and become blurry far from the centre.