Welcome to
Chapter 6 · Light
Explore dispersion, colour, galaxies and asteroids in this interactive science module.
6.3 Making Rainbows
Prisms, dispersion & the spectrum
6.4 Colours of Light
Primary colours, filters & seeing colour
6.5 Galaxies
The Milky Way, galaxy shapes & composition
6.6 Rocks in Space
Asteroids, Ceres & impacts on Earth
6.3 Making Rainbows
White light, dispersion and the spectrum
Newton's Discovery (1666)
Isaac Newton showed that white light could be split into different colours. He used a glass block shaped like a triangle — a triangular prism — to separate light from the Sun into a rainbow of colours on a screen.
This was a major discovery: white light is not a single colour — it is made up of many colours combined.
The Visible Spectrum
Dispersion
Dispersion means splitting white light into its different colours. It happens because each colour of light is refracted through a slightly different angle when it passes through a prism.
Red light
Refracted through the smallest angle
Violet light
Refracted through the largest angle
Triangular prism
A solid glass shape used to demonstrate dispersion
How Rainbows Form
A rainbow forms when water droplets in the air cause dispersion of sunlight. The light is also reflected from inside each droplet.
Sun must shine
Bright sunlight is needed as the light source
Rain or water drops
Droplets disperse the white light into colours
Sun behind you
Water drops reflect light back toward the observer
✅ Check Your Understanding — Q1
What name is given to the process of white light being split into different colours?
✅ Check Your Understanding — Q2
Which colour of light is refracted through the largest angle when passing through a prism?
✅ Check Your Understanding — Q3
Which condition is required to see a rainbow in the sky?
6.4 Colours of Light
Primary colours, adding, subtracting and seeing colour
Primary Colours of Light
Although white light contains seven colours, there are only three primary colours of light — colours from which all other colours of light can be made:
Adding Colours of Light
When primary colours of light overlap, they combine to produce new colours:
| Combination | Result |
|---|---|
| Red + Green | Yellow |
| Red + Blue | Magenta |
| Blue + Green | Cyan |
| Red + Green + Blue | White |
Subtracting Colours — Coloured Filters
A coloured filter only allows light of its own colour to pass through (transmitted). All other colours are absorbed. This is called subtraction of light.
Example: A red filter placed in front of white light — only red passes through; the other six colours are absorbed.
🔬 Interactive Filter Demo
Choose a filter colour — see what light gets through:
White light — all 7 colours present
Seeing Colours
When you look at a non-luminous object (one that doesn't emit its own light), you see the colour of light it reflects. All other colours are absorbed.
Yellow flower
Reflects yellow light, absorbs the other 6 colours
White object
Reflects all colours in white light equally
Black object
Absorbs all colours — reflects none
✅ Check Your Understanding — Q1
What are the three primary colours of light?
✅ Check Your Understanding — Q2
What colour is produced when red light and green light are added together?
✅ Check Your Understanding — Q3
A red filter is placed in front of white light. What happens to the other six colours of light?
6.5 Galaxies
The Milky Way, galaxy shapes and what galaxies are made of
The Milky Way
Our galaxy is called the Milky Way. On a clear night, far from city lights, you can see it as a milky band stretching across the sky. The word 'galaxy' comes from a Greek word meaning milky.
Shapes of Galaxies
Galaxies across the universe are classified into three main shapes:
Spiral
Arms wind out from a bright centre. Our Milky Way is this shape.
Elliptical
Oval or egg-shaped. Older, redder stars. The nearest galaxy (Canis Major Dwarf) is this shape.
Irregular
No definite shape. Often formed when galaxies collide or interact.
What Are Galaxies Made Of?
Galaxies are held together by gravity and contain:
Stars
Billions of stars, including suns like our own
Solar Systems
Stars with orbiting planets and moons
Gas
Vast clouds of gas spread throughout the galaxy
Stellar Dust
Fine dust particles found throughout space — Earth travels through a cloud of it!
Estimated stars in the Milky Way
Estimated galaxies in the universe
To cross the Milky Way at the speed of light
✅ Check Your Understanding — Q1
What shape is the Milky Way galaxy?
✅ Check Your Understanding — Q2
What force holds all the parts of a galaxy together?
✅ Check Your Understanding — Q3
Which of the following correctly lists what galaxies are made of?
6.6 Rocks in Space
Asteroids, the asteroid belt and impacts on Earth
What Are Asteroids?
Asteroids are objects made from rock that orbit the Sun. They range from 2 metres across (the smallest studied) up to 975 km in diameter. Most asteroids are irregular in shape — scientists describe them as shaped like potatoes.
Smallest studied
Just 2 metres across
Largest: Ceres
975 km diameter — discovered in 1801
Shape
Most are irregular, like potatoes
The Asteroid Belt
Most asteroids in our Solar System orbit the Sun in the asteroid belt — the region between the orbits of Mars and Jupiter. There are millions of asteroids there.
Asteroid Itokawa
Itokawa is one of the smallest asteroids visited by a spacecraft. It is about 530 m long and 250 m wide. In 2005, a spacecraft collected surface samples — giving scientists evidence about how the Solar System formed.
Itokawa appears to be made from lumps of rock from other broken small planets or moons. Tidal forces from passing planets can change its shape because its gravity is too weak to hold pieces firmly together.
Asteroids and Earth
Scientists estimate that a large asteroid impacts Earth on average every 130,000 years. Smaller asteroids hit far more frequently — but most break apart in the atmosphere.
Earth's gravity
Exerts a strong pull on passing asteroids
Orbital paths
Many asteroids have orbits that pass close to Earth
✅ Check Your Understanding — Q1
Where are most asteroids in our Solar System found?
✅ Check Your Understanding — Q2
What is the name of the largest known asteroid?
✅ Check Your Understanding — Q3
Why do asteroids sometimes impact with Earth? Select the best reason.
Match Activity
Match each term to its correct definition
Click a term on the left, then click its matching definition on the right. You need 5/6 to move on.
Terms
Definitions
🧪 Final Quiz
12 questions from all four topics — choose the best answer for each.
Well done!
You completed the Light module.
Certificate of Completion
Chapter 6 · Light
Grade 7 Science · Stage 8
Topics covered: Making Rainbows · Colours of Light · Galaxies · Rocks in Space