Refraction of Light at Curved Surfaces — Telangana (SSC) Class 10 Science Solutions (Free)

Refraction: Bending of light when it passes from one medium to another of different optical density. Snell's Law: n₁ sin θ₁ = n₂ sin θ₂ Where n = refractive index, θ = angle of incidence/refraction Light bends toward normal when entering denser medium, away from normal when entering rarer medium

Lens: A transparent optical device with curved surfaces for refraction of light. Convex lens (converging): Thicker at center, thinner at edges. Converges parallel rays to focal point. Forms real/virtual images. Concave lens (diverging): Thinner at center, thicker at edges. Diverges parallel rays. Forms only virtual, erect, diminished images. Both lenses obey lens formula and follow sign convention

Step 1: Given f = 20 cm, u = 40 cm (object distance) Step 2: Use lens formula 1/f = 1/v + 1/u Step 3: 1/20 = 1/v + 1/40 → 1/v = 1/20 - 1/40 = 1/40 Step 4: v = 40 cm (image distance) Step 5: Magnification m = v/u = 40/40 = 1 Image is at 40 cm, real, inverted, same size as object (magnification = 1)

Focal length (f): Distance between optical center and focal point of a lens. For convex lens, f is positive; for concave lens, f is negative. Power (P): Reciprocal of focal length in meters. P = 1/f (in diopters, D) Example: f = 20 cm = 0.2 m, P = 1/0.2 = +5 D (convex lens)

Step 1: Given f = -15 cm (concave, negative), u = 30 cm Step 2: Use lens formula 1/f = 1/v + 1/u Step 3: 1/(-15) = 1/v + 1/30 → 1/v = -1/15 - 1/30 = -3/30 = -1/10 Step 4: v = -10 cm Image forms at 10 cm on the same side as object, virtual, erect, diminished