Formula and example
How it is calculated
Fringe spacing Δy ≈ wavelength × screen distance ÷ slit separation
Worked example
A wavelength of 500 nm, slit separation of 0.5 mm and screen distance of 1 m give approximately 1 mm fringe spacing.
Things to check
- The formula describes the central region at small angles with a distant screen.
- A finite slit width also produces a diffraction envelope that affects the brightness of individual fringes.