Interference Fringe Spacing Calculator: Young's Double Slit

Young's Double Slit Experiment

Young's double slit experiment (1801) demonstrated the wave nature of light by producing interference fringes on a screen. When light passes through two slits, it diffracts and the waves interfere constructively (bright fringes) and destructively (dark fringes), creating a distinctive striped pattern.

🌈 Fringe Spacing Calculator

Free calculator for instant results.

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📐 Formula

Δy = λL / d

Δy = fringe spacing (m), λ = wavelength (m), L = distance to screen (m), d = slit separation (m). Bright fringe positions: y_m = mλL/d.

📝 Worked Example

Red laser (λ=633nm), slit separation d=0.1mm, screen L=1m:
Δy = (633×10⁻⁹ × 1) / (0.1×10⁻³) = 6.33 mm
Fringes visible every 6.33 mm on the screen

📝 How to Use

Enter Slit SeparationDistance d between the two slits in mm or μm.

Enter WavelengthWavelength of incident light in nm.

Enter Screen DistanceDistance L from slits to observation screen in meters.

Calculate Fringe SpacingView Δy and positions of all bright/dark fringes.

❓ FAQ

What happens to fringes when slit separation increases?

Fringes become closer together (Δy ∝ 1/d). Very close slits produce widely spaced, easily visible fringes.

Can electrons and atoms also create interference fringes?

Yes! De Broglie waves of electrons, neutrons, and even buckyballs (C₆₀) produce double-slit interference patterns — proving wave-particle duality.