Light – Reflection and Refraction – Class 10 Physics Chapter 9

Light – Reflection and Refraction

Light is a form of electromagnetic radiation that enables us to see. It travels in straight lines (rectilinear propagation) and has a speed of approximately 3 × 10⁸ m/s in vacuum.

Reflection of Light

Laws of Reflection:

1. The angle of incidence (i) equals the angle of reflection (r): ∠i = ∠r
2. The incident ray, reflected ray, and normal all lie in the same plane.

Spherical Mirrors

Property	Concave Mirror	Convex Mirror
Reflecting surface	Inner (cave) side	Outer (bulging) side
Focal length	Negative (real focus)	Positive (virtual focus)
Image formed	Real or virtual (depends on position)	Always virtual, erect, diminished
Uses	Torches, headlights, shaving mirrors, dentist mirrors	Rear-view mirrors in vehicles

Mirror Formula

1/v + 1/u = 1/f

Where: v = image distance, u = object distance, f = focal length

Magnification: m = -v/u = h'/h

Refraction of Light

Refraction is the bending of light when it passes from one transparent medium to another. It occurs due to a change in the speed of light.

Snell's Law:

n₁ sin i = n₂ sin r

or equivalently: n = sin i / sin r (refractive index of medium 2 w.r.t. medium 1)

Lenses

Property	Convex (Converging)	Concave (Diverging)
Shape	Thicker at centre	Thinner at centre
Focal length	Positive	Negative
Image	Real or virtual (depends on position)	Always virtual, erect, diminished
Uses	Magnifying glass, camera, spectacles (hypermetropia)	Spectacles (myopia), peepholes

Lens Formula

1/v - 1/u = 1/f

Magnification: m = v/u = h'/h

Power of a lens: P = 1/f (in metres). Unit: dioptre (D).

Reference: NCERT Science Textbook for Class 10 – Chapter 9; HC Verma Concepts of Physics; Lakhmir Singh Physics.