Practice question

**Wavefront** is locus of points in same phase, spherical from point source, plane at large distance because radius large, Huygens principle every point on wavefront acts as secondary source of wavelets, new wavefront envelope of secondary wavelets, allows prediction of new wavefront shape from known wavefront, explains reflection and refraction. Angular width 2θ = (2λ/a) . λ = 6.5 × 10⁻⁷ m , a = 5.0 × 10⁻⁶ m . sin θ = (λ/a) = (6.5 × 10⁻⁷/5.0 × 10⁻⁶) = 0.13 , θ = sin⁻¹(0.13) ≈ 7.5° , 2θ ≈ 15° . Using Δ = d sinθ, y = n λ D/d, a sinθ