Science · Class 10 · Light

Reflection and Refraction of Light

Aim: Distinguish between reflection and refraction of light, and relate them to everyday phenomena like mirrors and lenses.
  • Reflection — light bouncing back after striking a surface
  • Refraction — bending of light as it passes from one medium to another
  • Incident ray — the ray of light striking a surface
  • Normal — an imaginary line perpendicular to the surface at the point of incidence
  • Refractive index — a measure of how much a medium bends light
40 min lesson

Light · Concept 1 of 8

What is reflection?

  • Light bounces off a surface instead of passing through it
  • Happens with mirrors, water, polished metal, and even rough surfaces (diffused reflection)

Light · Concept 2 of 8

The two laws of reflection

  • The angle of incidence equals the angle of reflection
  • The incident ray, reflected ray, and normal all lie in the same plane

Light · Concept 3 of 8

Plane mirrors vs. spherical mirrors

  • Plane mirror: image is virtual, upright, same size, laterally inverted
  • Concave mirror: curves inward, can form real or virtual images depending on object distance
  • Convex mirror: curves outward, always forms a smaller, virtual, upright image — used in vehicle mirrors for a wider field of view

Light · Concept 4 of 8

What is refraction?

  • Light changes speed and bends when it passes from one transparent medium to another (e.g. air to water)
  • Cause: light travels at different speeds in different media
  • Classic evidence: a pencil looks 'bent' where it enters water

Light · Concept 5 of 8

Rules of refraction

  • Light bends towards the normal when entering a denser medium (e.g. air to glass)
  • Light bends away from the normal when entering a rarer medium (e.g. glass to air)
  • Light travelling along the normal does not bend at all

Light · Concept 6 of 8

Refractive index

  • Tells us how strongly a medium bends light
  • Higher refractive index = light slows down and bends more
  • Example: diamond has a very high refractive index — this is part of why it sparkles

Light · Concept 7 of 8

Lenses use refraction

  • Convex (converging) lens — bends light rays inward to a focus; used in magnifying glasses, human eye
  • Concave (diverging) lens — spreads light rays outward; used to correct short-sightedness

Light · Concept 8 of 8

Reflection and refraction around us

  • Rainbows — refraction and reflection of sunlight inside raindrops
  • Mirages — refraction of light through layers of air at different temperatures
  • Optical fibres — total internal reflection carries light (and data) over long distances

Quick Recap

Check Your Understanding

  1. 1State the two laws of reflection.
  2. 2Why does a pencil appear bent when placed in a glass of water?
  3. 3Name one real-world device or phenomenon each for reflection and for refraction.