What is fringe width?

Fringe width is the distance between the centers of two adjacent bright or dark fringes in an interference pattern.

In Young’s double-slit experiment (YDSE), coherent light from two slits overlaps on a screen to produce alternating bright and dark bands called interference fringes. The spacing of these bands is the fringe width. It tells how spread out the pattern is and depends on the wavelength of light, the slit separation, and the screen distance.

Formula (YDSE)

β = λD / d, where β is fringe width, λ is wavelength, D is distance from slits to screen, and d is slit separation.

How each factor affects fringe width

• Increase λ: Red light (longer λ) gives larger β than blue light.
• Increase D: Moving the screen farther increases β.
• Increase d: Making slits farther apart decreases β.

Typical measurements