Young's Double Slit — Interference Lab

Light Source

Wavelength (λ) 550 nm

c = λ · f

Frequency (f) 545 THz

400 THz (red) → 789 THz (violet) · c = 3×10⁸ m/s

380 nm Green 750 nm

Intensity 100%

Slit Geometry

Slit Separation (d) 0.50 mm

smaller d → wider fringes

Slit Width (a) 0.08 mm

controls diffraction envelope

Setup Geometry

Screen Distance (L) 100 cm

Δy = λL / d

Screen Width 5.0 cm

Display Options

Show Wavefronts

Animated superposition field

Diffraction Envelope

Single-slit modulation

Order Labels

m = 0, ±1, ±2…

Multi-wavelength

RGB composite pattern

Calculated Values

Fringe Width Δy

—

millimetres

Δy = λL / d

Visible Fringes

—

bright bands on screen

Path Difference (m=1)

—

nm = 1λ

Angular Fringe Width

—

degrees

θ = λ / d

λ = 550 nm · f = 545 THz

          d = 0.50 mm
           · 
          a = 0.08 mm
           · 
          L = 100 cm
        

Hover over field for intensity

Intensity Distribution I(y) — Position on Screen

How It Works

Coherent light passes through two slits separated by d. Each slit acts as a new point source of circular waves.

The field shows the real superposition. Where two crests meet → constructive (bright). Where crest meets trough → destructive (dark).

Bright fringes: d sinθ = mλ
Fringe spacing: Δy = λL / d
Intensity: I = I₀ cos²(πdy/λL)
× sinc²(πay/λL)
Speed of light: c = λ · f

Visible Spectrum

380–450 nm → Violet
450–495 nm → Blue
495–570 nm → Green
570–590 nm → Yellow
590–620 nm → Orange
620–750 nm → Red

f = c / λ c = 3×10⁸ m/s

Fringe Orders

m = 0 Central maximum

m = ±1 First order

m = ±2 Second order

m ≥ ±3 Higher orders