Diffraction
Send a wave through one opening and watch the transmitted field spread into a structured interference pattern. The amount of spreading depends on the opening size relative to the wavelength, not on a mysterious loss of direction at the slit.
The same wave can leave one opening as a narrow pattern and another as a broad fan.
Which matters more: the absolute width of the slit, or its width compared with the wavelength passing through it?
Change the two length scales and watch the far-field pattern respond.
The screen uses an idealized single-slit Fraunhofer intensity pattern. The model is normalized and dimensionless here so the ratio is easier to investigate.
The first modeled dark minimum appears at about 21.0°.
Try doubling both a and λ together. Then change only one of them. Which changes preserve the pattern shape, and which change the spread?
dimensionless scale ratio
ideal single-slit first zero
qualitative comparison only
Diffraction is a wave-scale effect: geometry measured in wavelengths controls the angular pattern.
Ray optics becomes a useful approximation when wavelength is tiny compared with the apertures and features that redirect the wave. When those scales become comparable, interference across the opening is visible in the transmitted field.
Aperture width and wavelength have the same unit, so their ratio has no unit. Similar ratios produce similar normalized patterns in this idealized model.
For an ideal single slit in the Fraunhofer regime, the first zero occurs where the path-difference geometry cancels the aperture contributions.
with β proportional to (a/λ) sinθ. This captures the central maximum and weaker side lobes of the ideal slit.
Real apertures have thickness, finite illumination, imperfect coherence, detector response, polarization effects, near-field/far-field differences, and other details. The formulas here describe an idealized scalar-wave single-slit model.
The single-slit pattern is coherent and structured. Changing aperture geometry changes the interference pattern predictably in the ideal model.
The angular distribution changes. The normalized display rescales brightness for visibility and does not track total transmitted power through different slit widths.
With λ fixed at 0.45 units, place the first dark minimum near 25°.
Adjust aperture width, then check your setting. This is an inverse use of the same relationship: target pattern → required geometry.
arbitrary length units
ideal first minimum
within ±1° counts