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.
Drag either source. The colourless lines that never move are nodal lines, where the two waves are exactly out of phase
Source separation—
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Show
Sources
Source separation—
Wavelength—
troughcrest
What to observe
- Watch the waves stream out: the nodal lines stay put while crests and troughs pass on either side. Along them the two paths differ by half a wavelength, so the waves cancel.
- Switch to time-averaged intensity. The moving ripples average away and only the fixed fringes remain: bright where the waves add, blank where they cancel.
- Move the sources farther apart or shorten the wavelength and the fringes crowd together. Their spacing is set by λ / separation, the double-slit formula.
- Drop to 1 source: plain circular ripples and no fringes. Interference needs two coherent waves.
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