Light interference — Young’s experiment

Equipment

• Coherent source through two slits — “Wavelength λ” slider (400–700 nm)
• “Slit separation a” and “Screen distance D” sliders
• Fringe screen with intensity plot and fringe-spacing readout
• “Reset parameters” button

Procedure

1. Hold a and D, sweep the wavelength

   Fix “Slit separation a” and “Screen distance D”; drag “Wavelength λ” from 400 to 700 nm and watch the fringes spread. Record the readout i (mm) at two wavelengths and check that i₂/i₁ ≈ λ₂/λ₁ from $i = \lambda D/a$.

2. Sweep a and D, build a comparison table

   Decrease a then increase D in turn; each time read i and tabulate it against $\lambda D/a$. Check that i is inversely proportional to a and proportional to D; use “Reset parameters” to return to the standard configuration between measurements.

3. Predict the fringe order by color

   Set λ to the two ends of the spectrum and predict which pattern is wider before looking; explain why the experiment let Young measure visible-light wavelengths without any microscope — only a ruler for the fringe spacing.

Simulation

Experiment history

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