12
CBSE Marks
★★★★★
Difficulty
10
Topics
Very High
Board Weight
Topics Covered
10 key topics in this chapter
Reflection of Light
Laws of Reflection
Spherical Mirrors: Concave & Convex
Mirror Formula & Magnification
Refraction of Light
Laws of Refraction (Snell's Law)
Refractive Index
Refraction through Lenses
Lens Formula & Magnification
Power of a Lens
Study Resources
Key Formulas & Reactions
| Formula / Reaction / Rule | Expression |
|---|---|
| Mirror Formula | \(1/v + 1/u = 1/f\) |
| Mirror Magnification | \(m = −v/u = h_i / h_o\) |
| Snell's Law | \(n₁ sin θ₁ = n₂ sin θ₂\) |
| Refractive Index | \(n = c/v = sin i / sin r\) |
| Lens Formula | \(1/v − 1/u = 1/f\) |
| Lens Magnification | \(m = v/u\) |
| Power of Lens | \(P = 1/f(m) unit: Dioptre (D)\) |
| Combined Power | \(P = P₁ + P₂\) |
Important Points to Remember
Mirror formula: 1/v + 1/u = 1/f. Magnification m = −v/u. Sign convention: distances measured from pole; incident ray direction is positive.
Concave mirrors form real, inverted images (except when object is within F). Convex mirrors always form virtual, erect, diminished images.
Snell's Law: n₁ sin θ₁ = n₂ sin θ₂. Light bends toward normal when entering denser medium (n > 1).
Lens formula: 1/v − 1/u = 1/f. Power P = 1/f (in metres), unit is Dioptre (D). Convex lens has positive power.