Constructive interference from two coherent slits occurs when their path difference is an integer number of wavelengths.
Difficulty
Intermediate
Read time
5 min
Prerequisites
Basic algebra, consistent units, and the stated model assumptions
Source
OpenStax, College Physics 2e, §27.3 (Paul Peter Urone and Roger Hinrichs)OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.
Constructive interference from two coherent slits occurs when their path difference is an integer number of wavelengths. Bright-fringe positions therefore depend on wavelength and slit separation.
| Symbol | Meaning | Units |
|---|---|---|
| Slit center-to-center spacing | ||
| Bright-fringe angle from the central axis | ||
| Integer bright-fringe order | ||
| Wavelength |
Relate bright-fringe angle to wavelength.
Infer wavelength from a known slit separation.
For slit spacing 2.00 × 10⁻⁵ m, a first-order bright fringe occurs at the listed angle in radians. Find the wavelength.
OpenFormulaGraph equation reference; FormuLab adaptation details and license are provided below.
Adapted from OpenFormulaGraph, under CC BY 4.0.
FormuLab adapted wording, notation, applicability conditions and topic placement, and expanded the numerical check into a worked example.
Assumptions
FormuLab is a study reference. Verify formulas, units, assumptions, and course-specific conventions before relying on them.
© 2026 FormuLab. All rights reserved.