Young's double slit
Intermediate
Bright and dark fringes from two slits.
β = λD/dLight from two narrow slits forms bright and dark fringes on a screen. Bright when path difference = nλ: d sinθ = nλ.
d = 0.2 mm, D = 1.5 m, λ = 550 nm: β = 4.1 mm.
Small angles allow sinθ ≈ y/D.
In more detail
Young's double-slit experiment shows interference by passing light through two narrow slits. Bright and dark fringes appear on a screen where waves reinforce or cancel.
Real-world uses
- Young's experiment proved the wave nature of light.
- It is used to measure wavelengths in teaching labs.
- Physicists use Young's double slit experiment to show that light is a wave and to measure its wavelength.
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Frequently asked questions
Why are there bright and dark fringes?
Waves from the two slits add in phase at bright fringes and out of phase at dark ones.
What determines the fringe spacing?
The wavelength, the slit separation and the distance to the screen.
Why must the light be coherent?
The two slits must have a fixed phase relationship for a stable interference pattern to appear.
Related topics in Optics
Wave theory of light · Huygens' principle · Coherent sources · Fringe width · Intensity in interference · Thin film interference