Two coherent sources S₁ and S₂ each produce intensity I₀ at the screen. Their wavelength is 0.5 μm, separation d=2 mm, and screen distance L=2 m. Find the intensity at point A shown in the source figure.

Question

G1 Physics · Accepted Answer

At A, S₁A=L and S₂A=√(L²+d²). For d≪L, δ≈d²/(2L)=(2×10⁻³)²/(4)=1×10⁻⁶ m=2λ. Thus the waves arrive in phase. Each source gives intensity I₀, so the resultant is 4I₀. Option A.