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Physics

Double Slit Fringe Spacing Calculator

Estimate bright-fringe separation in a two-slit interference pattern.

SI units shown beside each fieldIdeal model explained below
Physics lab
Physics lab

Use the units beside each input and review the model assumptions.

See the method

Define your system

Runs on your device

Your calculated quantity

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter wavelength, screen distance, slit separation.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

For small angles, fringe spacing Δy = λL/d.

A WORKED EXAMPLE

Using wavelength = 550 nm, screen distance = 2 m, slit separation = 0.5 mm, the result is 2.2 mm. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

Far-field small-angle approximation. Slit width affects the diffraction envelope but is not included in the spacing formula.

What to keep in mind

Far-field small-angle approximation. Slit width affects the diffraction envelope but is not included in the spacing formula. An idealized educational model using the stated SI units. Real systems may need additional forces, losses or experimental measurements. Not a safety or equipment specification.

Common questions

How do I use this double slit fringe spacing calculator?

Estimate bright-fringe separation in a two-slit interference pattern. Enter wavelength in nm, screen distance in m, slit separation in mm. The starting example is editable; use values for the same system or project.

Which assumptions affect this result?

Far-field small-angle approximation. Slit width affects the diffraction envelope but is not included in the spacing formula.

Methodology maintained by ClarityKit. How these tools are built and checked.