🔦 Introduction

Light is a form of energy that enables us to see objects. In this chapter, we study how light behaves when it reflects off surfaces and passes through different media.

🪞 1. Reflection of Light

Reflection: Bouncing back of light when it strikes a smooth surface.

🔹 Laws of Reflection:

  1. The incident ray, the reflected ray, and the normal all lie in the same plane.

  2. Angle of incidence (∠i) = Angle of reflection (∠r)

🔹 Types of Reflection:

  • Regular Reflection: From a smooth surface, like a mirror

  • Diffuse Reflection: From a rough surface

🔹 Image Formed by Plane Mirror:

  • Virtual and Erect

  • Same size as object

  • Laterally inverted

  • Same distance behind the mirror

🔭 2. Spherical Mirrors

Spherical mirrors are curved mirrors:

  • Concave Mirror: Curved inward

  • Convex Mirror: Curved outward

Important Terms:

  • Pole (P): Center of mirror surface

  • Center of Curvature (C): Center of the sphere

  • Principal Axis: Line passing through C and P

  • Focus (F): Point where parallel rays meet or appear to diverge from

  • Focal Length (f): Distance between P and F (f = R/2)

🔹 Rules for Ray Diagrams:

  1. A ray parallel to axis passes through F (concave) or appears to diverge from F (convex)

  2. A ray through C reflects back on itself

  3. A ray through F becomes parallel to axis after reflection

  4. A ray incident at pole reflects symmetrically

🔹 Uses:

  • Concave Mirror: Shaving mirror, solar cooker, headlights

  • Convex Mirror: Rear-view mirror

🔍 3. Mirror Formula and Magnification

Mirror Formula: Where:

  • f = focal length

  • v = image distance

  • u = object distance

Magnification (M): Where:

  • h' = height of image

  • h = height of object

💡 4. Refraction of Light

Refraction: Bending of light as it passes from one medium to another.

🔹 Laws of Refraction:

  1. Incident ray, refracted ray, and normal lie in the same plane

  2. (Snell’s Law)

Refractive Index (n):

🔎 5. Lenses

Lenses are transparent objects with curved surfaces:

  • Convex Lens: Converging lens

  • Concave Lens: Diverging lens

🔹 Image Formation by Lenses:

Use similar rules as mirrors for ray diagrams:

  1. Parallel ray passes through F

  2. Through optical center (passes undeviated)

  3. Through F emerges parallel

🔹 Lens Formula:

Magnification (M):

🔹 Power of a Lens:

Unit: Dioptre (D)

✅ Key Points to Remember

  • Light reflects according to the laws of reflection.

  • Concave mirrors form real or virtual images depending on object position.

  • Refraction occurs due to change in speed of light in different media.

  • Convex lenses converge light; concave lenses diverge it.

  • Mirror and lens formulas help in numerical calculations.