Wave Optics Part 2

Concept:A plane wave remains plane after refraction through a prism, but a small aperture causes diffraction and spherical wavefront.Explanation:When a plane wave passes through a prism, all parts travel at the same speed through the medium.The wavefront tilts due to refraction but remains flat and parallel, so it stays a plane wave.Thus, Statement I is true.According to Huygens' Principle, every point on a wavefront acts as a source of secondary spherical wavelets.When a plane wave encounters a pinhole comparable to the wavelength ($\lambda$), diffraction occurs and the emerging light spreads spherically.Hence, Statement I is true.For a slit of width $d$, the angular spread due to diffraction is $\theta \approx \frac{\lambda}{d}$.As slit width increases, $\theta$ decreases; the wavefront becomes flatter, meaning curvature decreases.Curvature is the reciprocal of the radius of the wavefront, so increasing slit width reduces curvature.Therefore, Statement II is false.Answer:Statement I is true but Statement II is false. Correct option is C.