In the double-slit experiment, the fringe separation (also called fringe width) is directly proportional to the wavelength of light.
This means:
- If the wavelength increases, the distance between adjacent bright (or dark) fringes increases.
- If the wavelength decreases, the fringes get closer together.
More specifically, the fringe separation depends on the wavelength, the distance between the slits, and the distance from the slits to the screen. So, for a fixed slit separation and screen distance, changing the wavelength changes the fringe spacing proportionally.
In short, longer wavelengths produce wider spaced fringes, and shorter wavelengths produce narrower spaced fringes in the interference pattern.