Physics
Wave Interference
Two sources send out ripples that cross and combine. Where crests meet crests the wave doubles; where crest meets trough it cancels to stillness. Those cancellations trace the dark fringes behind the double-slit experiment.
Source separation—
Wavelength—
troughcrest
Drag either white source. The dark lines that never move are nodal lines, where the two waves are exactly out of phase and cancel.
What to observe
- Follow one of the dark bands: it stays put while the waves stream through it. Along that line the two sources are always a half-wavelength out of step, so they cancel. This is destructive interference.
- Move the sources farther apart or shorten the wavelength and the fringes crowd together. It is the ratio λ / separation that sets their spacing, exactly the double-slit formula.
- Drop to 1 source: plain circular ripples, no fringes. Interference needs at least two coherent waves to add and subtract.
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