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Chapter 10 · Sample

Light — Reflection and Refraction

Class 10 · Physics · Reading time ≈ 6 min · 3 practice questions

Light enables us to see the world around us. In this chapter we study how light behaves when it strikes a surface (reflection) and when it passes from one medium into another (refraction) — two phenomena behind mirrors, lenses, spectacles, and even the twinkling of stars.

10.1 Reflection of Light

📘 Definition
When light falls on a smooth, polished surface and bounces back into the same medium, the phenomenon is called reflection of light.

Laws of Reflection

Reflection follows two simple laws, true for all surfaces — plane or curved:

1. The angle of incidence is always 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.

⭐ Exam Point
The image formed by a plane mirror is always: virtual and erect, of the same size as the object, laterally inverted, and as far behind the mirror as the object is in front of it. Questions on lateral inversion appear very frequently.

10.2 Spherical Mirrors

A spherical mirror is a mirror whose reflecting surface is part of a hollow sphere. There are two types — and comparing them is a favourite exam question:

Concave Mirror Convex Mirror
Reflecting surface Curved inwards (like a cave) Curved outwards
Image Real or virtual, depending on object position Always virtual, erect and diminished
Common uses Shaving mirrors, torches, solar cookers, dentist's mirror Rear-view mirrors in vehicles, security mirrors
🧮 Mirror Formula
1⁄v  +  1⁄u  =  1⁄f
v = image distance · u = object distance · f = focal length  |  Also: f = R/2, where R is the radius of curvature

10.3 Refraction of Light

📘 Definition
The bending of light as it passes obliquely from one transparent medium into another (for example, air to water) is called refraction of light. It happens because light travels at different speeds in different media.

This is why a pencil half-dipped in water appears bent, a pool looks shallower than it is, and stars appear to twinkle as their light bends through layers of the atmosphere.

⭐ Exam Point
When light goes from a rarer to a denser medium (air → glass), it bends towards the normal. From denser to rarer (glass → air), it bends away from the normal. Students most often lose marks by mixing these up.

Practice Questions

Tap an option to check yourself — the answer and explanation appear below the question.

Question 1
A convex mirror is preferred as a rear-view mirror in vehicles because it:
  1. aforms real and magnified images
  2. bforms inverted images of vehicles behind
  3. cgives a wider field of view with erect, diminished images
  4. dabsorbs less light than a plane mirror
✔ Correct answer: (c)
A convex mirror always forms erect, diminished, virtual images, allowing the driver to see a much wider area behind the vehicle in a small mirror.
Question 2
The focal length of a spherical mirror with radius of curvature 30 cm is:
  1. a60 cm
  2. b15 cm
  3. c30 cm
  4. d7.5 cm
✔ Correct answer: (b)
Using f = R/2 = 30/2 = 15 cm. Remember this relation — it is asked directly as well as inside numericals.
Question 3
A ray of light travelling from air into glass slab bends:
  1. atowards the normal
  2. baway from the normal
  3. calong the normal without bending
  4. dbackwards into air
✔ Correct answer: (a)
Glass is denser than air, so light slows down and bends towards the normal — the rarer-to-denser rule.
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