A transparent block A having refractive index μ = 1.25 is surrounded by another medium of refractive index μ = 1.0 as shown in figure. A light ray is incident on the flat face of the block with incident angle θ as shown in figure. What is the maximum value of θ for which light suffers total internal reflection at the top surface of the block?
❓ Question A transparent block A having refractive index μ = 1.25 \mu = 1.25 is surrounded by another medium of refractive index μ = 1.0 \mu = 1.0 (air). A light ray is incident on the flat vertical face of the block with incident angle θ \theta θ (in air) as shown in the figure. What is the maximum value of θ \theta for which the light suffers total internal reflection at the top horizontal surface of the block? (Assume the top surface is horizontal and the vertical face is flat — standard rectangular block geometry.) 🖼️ Question Image ✍️ Short Solution Step 1 — Snell’s law at the vertical face Air ( n 1 = 1.0 ) (n_1=1.0) → block ( n 2 = 1.25 ) (n_2=1.25) . At the vertical face: n 1 sin θ = n 2 sin r ⇒ sin r = n 1 n 2 sin θ = 1 1.25 sin θ = 0.8 sin θ . Here r r is the angle the refracted ray makes with the normal to the vertical face (i.e. with the horizontal direction). Step 2 — Angle of incidence at the top (hori...