Light – Reflection and Refraction — Part 3: Refraction of light: visual lesson, CBSE Class 10 Science

Lesson

Refraction of light

Part 3 — why light bends when it passes from one medium into another, and how we measure that bending.

In this lesson you will

Explain refraction using everyday examples
State the laws of refraction and trace a ray through a rectangular glass slab
Calculate absolute and relative refractive index from speeds of light

Concept

What is refraction?

Light travels at different speeds in different media. When it passes obliquely from one transparent medium into another, its speed changes and so does its direction. This change of direction is refraction.

Table of four everyday observations caused by refraction
Everyday observation	Explained by
Pencil looks bent at the water surface	Light from the submerged part bends as it leaves water
Bottom of a pond looks shallower	Rays bend away from the normal as they leave water
Letters look raised under a glass block	Refraction at the glass surfaces
Lemon looks larger in a glass of water	The curved glass and water bend light like a lens

Diagram

Refraction through a glass slab

Drawn for refractive index 1.5 and an angle of incidence of 45°, so the angle of refraction is about 28°.

Entering glass from air, the ray bends towards the normal (r < i). Leaving glass into air, it bends away from the normal. In a slab with parallel faces, the emergent ray is parallel to the incident ray, but shifted sideways: the lateral shift.

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