PhysicsChapter 4: Diffraction and Interference
Interference of Light and Coherent Sources
Light interference
Definition
Light interference is the formation of alternating regions of greater and smaller intensity when coherent light waves overlap. Coherent sources maintain the same frequency and a constant phase difference.
Coherent Sources
Stable interference fringes require waves with a predictable phase relationship. For stable fringes, sources should have: the same frequency, a constant phase difference, and preferably comparable amplitudes. Two independent ordinary lamps usually do not maintain a fixed phase relation. Therefore, Young's experiment uses two slits illuminated by the **same initial source**. The slits then behave as coherent secondary sources.
Bright Fringes
**Δr=nλ**
Dark Fringes
**Δr=(n+½)λ Interference is important evidence for the wave nature of light**.
Formula / Key Relation
**I=I₁+I₂+2√(I₁I₂)cosΔφ**
Exam preparation
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Review the key facts, formulas and checks before you move on.Interference of Light and Coherent Sources
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COHERENT
- same frequency
- constant phase difference
- → stable fringes
60-second revision
- Stable light interference requires coherence.
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