Practice question

**Frequency of light** remains unchanged when refracts from air into water because frequency determined by source, energy E= h f conserved, speed decreases v= c/n, wavelength decreases λ'=v/f= λ/n, energy of wave proportional to amplitude² not speed, intensity I =½ c ε₀ E₀², energy not depend on speed directly, when speed decreases amplitude may change but energy conserved, interference redistributes energy, total energy same, bright regions gain from dark. Bright fringe position x_n = (n λ D/d) . For the fifth bright fringe, n = 5 . λ = 4.9 × 10⁻⁷ m , d = 5.0 × 10⁻⁴ m , D = 1.0 m