Board exam focus — Light – Reflection and Refraction (CBSE & HBSE)

Covers the fundamental principles of light, including reflection by mirrors and refraction by lenses. CBSE focuses on ray diagrams and numerical problems; HBSE focuses on definitions and sign conventions.

Reflection and Spherical Mirrors

Reflection is the phenomenon of light bouncing back when it hits a polished surface.

1. Laws of Reflection

1. The angle of incidence is equal to the angle of reflection (∠i = ∠r).
2. The incident ray, the reflected ray, and the normal at the point of incidence, all lie in the same plane.

2. Spherical Mirrors

• Concave Mirror: Reflecting surface is curved inwards. It is a Converging mirror.
• Convex Mirror: Reflecting surface is curved outwards. It is a Diverging mirror.

3. Key Terms

• Pole (P): Center of the reflecting surface.
• Principal Axis: Straight line passing through the Pole and Center of Curvature.
• Focus (F): Point where parallel rays meet (or appear to meet) after reflection.
• Focal Length (f): Distance between Pole and Focus. Relation: R = 2f.

Mirror Formula and Magnification

1. Sign Convention (Cartesian)

• Object is always on the left (-u).
• Distances in the direction of incident light are positive (+).
• Heights above principal axis are positive (+).

2. Mirror Formula

1/v + 1/u = 1/f

• v = Image distance, u = Object distance, f = Focal length.

3. Magnification (m)

m = h' / h = -v / u

• If m is negative, image is Real & Inverted.
• If m is positive, image is Virtual & Erect.
• If |m| > 1, image is enlarged.

Refraction of Light

Refraction is the bending of light when it travels from one medium to another due to change in speed.

1. Laws of Refraction (Snell's Law)

1. The incident ray, refracted ray, and normal lie in the same plane.
2. Snell's Law: The ratio of sine of angle of incidence to the sine of angle of refraction is constant for a given pair of media.

• sin i / sin r = constant (n)

2. Refractive Index (n)

n₂₁ = Speed of light in medium 1 / Speed of light in medium 2

• Absolute Refractive Index (nₘ) = c / v (where c is speed of light in vacuum).
• Light bends towards the normal when moving from Rarer to Denser medium.
• Light bends away from the normal when moving from Denser to Rarer medium.

Spherical Lenses

A lens is a transparent material bound by two surfaces, at least one of which is spherical.

1. Types of Lenses

• Convex Lens: Thicker at middle, thinner at edges. Converging lens.
• Concave Lens: Thinner at middle, thicker at edges. Diverging lens.

2. Lens Formula and Magnification

1/v - 1/u = 1/f

• Magnification (m) = h' / h = v / u

3. Power of a Lens (P)

The degree of convergence or divergence of light rays.

• P = 1 / f (in meters)
• Unit: Dioptre (D).
• Convex lens has +ve power; Concave lens has -ve power.

Frequently asked questions

Are these Light – Reflection and Refraction notes free?

Yes — the Light – Reflection and Refraction notes for Science (Class 10) on Siksha Sarovar are completely free to read, with no account required.

Do these notes follow CBSE and HBSE?

Yes. The Light – Reflection and Refraction notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

What does the Light – Reflection and Refraction chapter cover?

Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Light – Reflection and Refraction.