---
title: "Refraction and Lenses"
description: "A wave changes direction at a boundary because its speed changes there, while its frequency stays the same. Converging and diverging lenses use that bending, and a ray diagram shows where the image fo"
canonical: https://lightmysky.com/learn/science/refraction-and-lenses-mt_u8GKuBMmzC
source: https://lightmysky.com/learn/science/refraction-and-lenses-mt_u8GKuBMmzC.md
retrieved: 2026-09-12
---

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# Refraction and Lenses

A wave changes direction at a boundary because its speed changes there, while its frequency stays the same. Converging and diverging lenses use that bending, and a ray diagram shows where the image forms and what it looks like.

Subject: Science · Area: Waves, Light & Sound · Ages 15 to 16
Page: https://lightmysky.com/learn/science/refraction-and-lenses-mt_u8GKuBMmzC

## Ready when they can

- Explains bending at a boundary by the change in speed, and says which of speed, frequency and wavelength change
- Draws a ray diagram for a converging lens with the object beyond and inside the focal length
- Describes an image as real or virtual, upright or inverted, magnified or reduced

## Lesson: Bending light with glass

A straw looks bent in a glass because light changes speed when it enters water, and a speed change bends the ray. Bending toward the normal happens entering a slower medium, and away from the normal leaving it. Only speed and wavelength change at the boundary, since the frequency is fixed by the source.

**Example.** Ella holds a magnifying glass close over a stamp. The object sits inside the focal length, so the rays spread as if from a bigger upright stamp behind the lens. She sees a virtual magnified image. Sliding the stamp beyond the focal length would flip it to a real inverted image a screen could catch, like a camera.

A converging lens is fat in the middle and pulls parallel rays together at its focal point. The image depends entirely on where you park the object. Beyond the focal length you get a real inverted image, and inside it you get a virtual upright magnified one. Bigger steps in refractive index mean stronger bending.

**Tip.** Describe every image with three words: real or virtual, upright or inverted, magnified or reduced. Total internal reflection is the extreme case, when light trying to leave glass is trapped instead, and fibre optics ride on exactly that trick to pipe signals around corners.

**Recap.** Speed change bends the ray, and lens position picks the image.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Ray Diagrams & Images](https://lightmysky.com/learn/science/ray-diagrams-and-images-mt_FVERuBoCD1)
- [Reflection & Refraction](https://lightmysky.com/learn/science/reflection-and-refraction-mt_PifbJOuXrG)
- [The Wave Equation](https://lightmysky.com/learn/science/the-wave-equation-mt_wmKhTiXt1p)

## Opens up

- [Huygens's Principle and the Laws of Reflection and Refraction](https://lightmysky.com/learn/science/huygenss-principle-and-the-laws-of-reflection-and-refraction-mt_xxdniF2__w)