VCE Physics · Wave Interference

Young's Double Slit

Two coherent sources, one screen. Set the optics (λ, d, L) to change the fringe spacing on the wall, then set the path difference (PD) at the screen and see whether the waves meet in phase (bright) or antiphase (dark).

Intensity on screen

Optics

Wavelength λ550 nm

Slit separation d0.20 mm

Slit–screen distance L1.50 m

Fringe spacing Δy = λL/d. The viewing window on the wall is fixed, so wider fringes mean fewer bands in view. The PD you have set is held at the same number of wavelengths, so the probe and rays move to wherever that PD now occurs.

Animation

Path Difference (PD)1.0 λ

Time (s)0.00 s

Show

Path rays Fringes Antinode lines Wavefronts

0.0 λ

At probe

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Spacing Δy

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Probe y

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Condition

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Constructive (bright): PD = nλ

Destructive (dark): PD = (n + ½)λ

n = 0, 1, 2, … (order). VCAA convention.