Waves · free physics game
Interference Tuner
Set λ so the first bright fringe lands on the detector at 1.10 mm.
Interference Tuner play area
(430 nm × 2.00 m) ÷ 1.000 mm0.860 mmSolve x = λD/a, drag the glowing piece of the bench into place, then lock it.
How the physics works
- Simple definition
- Interference fringes appear where waves from two coherent sources arrive with a path difference of a whole number of wavelengths.
- Example
- Slits 1.00 mm apart lit by 550 nm light throw fringes 1.10 mm apart on a screen 2.00 m away, because x = λD/a.
Light passing through two narrow slits arrives at a point on the screen by two slightly different routes. For small angles the extra distance travelled from the far slit is a·y/D. Where that equals a whole number of wavelengths, nλ, crests meet crests and the point is bright; where it equals an odd number of half wavelengths, (n + ½)λ, a crest meets a trough and the point is dark.
Setting a·y/D = nλ gives evenly spaced fringes: the spacing is x = λD/a, the nth bright fringe sits at n·x and the nth minimum at (n + ½)·x. A longer wavelength, a more distant screen or closer slits all spread the pattern out — which is the whole of this game. Drag the slits together and watch the fringes breathe apart; drag the lamp through the spectrum and the beam recolours because λ is the colour. The screen window here is ±12 mm, and the dial moves in real steps, so the value you calculate is the value you can set.
The two other standard results of this topic have their own pages: a ruled grating obeys d sinθ = nλ in Diffraction Gratings, and a driven wire obeys fₙ = (n/2L)√(T/μ) in Stationary Waves.