PhysicsDouble slit interferenceUniversity
AQAEdexcelOCRAPIBCambridge

Double-Slit Fringe Spacing Calculator

Calculates the spacing between adjacent bright fringes in a double-slit interference pattern.

Use the free calculatorCheck the variablesOpen the advanced solver
Open Advanced Calculator
This is the free calculator preview. Advanced walkthroughs stay in the app.
Result
Ready
Fringe Spacing

Formula first

Overview

Under the small-angle approximation, the distance between interference fringes is proportional to the screen distance and the wavelength of light used. As the slit separation increases, the spacing between these fringes decreases inversely.

Symbols

Variables

D = Fringe Spacing, L = Screen Distance, = Wavelength, d = Slit Spacing

Fringe Spacing
Screen Distance
Wavelength
Slit Spacing

Apply it well

When To Use

When to use: Use this formula to find the distance between neighboring bright fringes on a screen when light passes through two slits.

Why it matters: This calculation allows for the experimental determination of light wavelength using simple laboratory geometry.

Avoid these traps

Common Mistakes

  • Placing the slit spacing (d) in the numerator instead of the denominator.
  • Failing to convert units like millimeters or nanometers into base meters.

One free problem

Practice Problem

A screen is 2.0 m away, the slit spacing is 1.0e-3 m, and the wavelength is 5.0e-7 m. What is the fringe spacing?

Screen Distance2 m
Wavelength5e-7 m
Slit Spacing0.001 m

Solve for:

Hint: Multiply the screen distance by the wavelength, then divide by the slit spacing.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. University Physics Volume 2 (OpenStax) - Chapter 17.3 Double-Slit Interference
  2. Halliday, Resnick, and Walker, Fundamentals of Physics
  3. Hecht, Optics
  4. NIST CODATA
  5. Hecht, Eugene. Optics.
  6. Jenkins, Francis A., and Harvey E. White. Fundamentals of Optics.
  7. Wikipedia, "Double-slit experiment"
  8. University Physics textbooks, e.g., Young & Freedman, Serway & Jewett