Practice question

**Double-slit vs single-slit** double-slit interference pattern has equally spaced bright fringes with envelope due to single-slit diffraction, single-slit central maximum width 2λ D/a, intensity of secondary maxima decreases with order, condition for coherence constant frequency and phase, path difference for bright n λ, dark (n+½)λ. Dark fringe position x_n = ((n + (1/2)) λ D/d) . For the fifth dark fringe, n = 4 . λ = 6.5 × 10⁻⁷ m , d = 5.0 × 10⁻⁴ m , D = 1.0 m . x₄ = ((4 + (1/2)) × 6.5 × 10⁻⁷ × 1.0/5.0 × 10⁻⁴) = (4.5 × 6.5 × 10⁻⁷/5.0 × 10⁻⁴)