TCE Physics — Level 4
Wave Interference — Flashcards & Quiz
Wave interference occurs when two or more waves overlap, producing regions of enhanced (constructive) or cancelled (destructive) amplitude. TCE Physics Level 4 uses Young's double-slit experiment as the canonical example, and expects you to apply path-difference conditions to predict bright and dark fringes, calculate fringe spacing, and explain why interference is evidence for the wave nature of light.
Key Points
- Constructive interference: waves arrive in phase, amplitudes add. Path difference = nλ (n = 0, 1, 2, ...).
- Destructive interference: waves arrive out of phase, amplitudes cancel. Path difference = (n + ½)λ.
- Young's double-slit: two coherent light sources produce bright and dark fringes on a distant screen.
- Fringe spacing formula: Δy = λL/d, where L is the slit-to-screen distance and d is the slit separation.
- Young's experiment provided historical evidence for the wave nature of light (vs Newton's particle theory).
- Coherent sources have a constant phase difference — typically achieved by splitting one source into two.
Common Mistakes to Avoid
- Confusing path difference (∆) with phase difference — they're related but different.
- Using nλ for destructive interference and (n+½)λ for constructive — it's the other way.
- Forgetting the small-angle approximation for fringe spacing (valid when fringe spacing << slit-to-screen distance).
- Missing that coherent sources are required — incoherent sources average out the interference pattern.
- Using wavelength in cm in a formula expecting metres.
Exam Strategy
TASC Level 4 interference questions give experimental parameters (slit separation, wavelength, distance) and ask for fringe spacing or position of bright/dark fringes. Method: (1) identify known quantities, (2) apply Δy = λL/d for fringe spacing, (3) use path difference conditions to find specific fringe positions, (4) check units. Diagrams of the experimental setup add clarity.
Revision Tip
Young's double-slit calculations are drillable — build a Revizi deck with 8+ problems varying which parameter is the unknown (λ, d, L, or Δy).
Last updated: March 2026