Superposition & Interference Challenge
25 NEET-standard questions on the principle of superposition, coherent and incoherent addition of waves, intensity, constructive and destructive interference, and why two bulbs give no fringes. Answer each one. If you get it wrong, Vidya Ma’am explains it with an animated movie you can control, a slider to play with, and a step-by-step solution. Then try again.
NCERT Physics XII Part II · Ch. 10 · pp. 262–265Keys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
“Coherent = add amplitudes”Coherent: add the displacements, then square. Incoherent: add the intensities.Two bulbs: I = I₁ + I₂
Phase from pathφ = (2π/λ) × Δ1 wavelength = 2π; 2.5λ = 5π
Bright (constructive)Δ = nλ, φ = 0, ±2π, …I = 4I₀ for equal sources
Dark (destructive)Δ = (n + ½)λ, φ = ±π, ±3π, …I = 0 for equal sources
Any pointI = 4I₀ cos²(φ/2)Unequal: I = I₁ + I₂ + 2√(I₁I₂) cos φ
Ratio of extremesImax/Imin = ((a₁+a₂)/(a₁−a₂))²Take square roots of intensities first
Incoherent averageI = 2I₀ everywhereOrdinary sources change phase in ~10⁻¹⁰ s
Young’s trickOne pinhole S lights S₁ and S₂, so their phases are locked.Two sodium lamps give no fringes
right first tryfixed after explanationstill to fix
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