Light Bounces, Bends and Is Soaked Up
- Physics
- Ages 11–14 · Grades 6–8
- Hands-on experiment
What you’ll find out
- Light reflects, refracts, is absorbed or passes through, often several at once.
- Reflection follows a rule: the angle in equals the angle out.
- Colour comes from which light a surface reflects and which it absorbs.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Bouncing and bending
When light meets a surface, three things can happen: it can bounce off, pass through, or be soaked up. Usually some of each happens at once. A mirror reflects almost all of it, and it follows a rule: the angle the light arrives at equals the angle it leaves. A rough wall reflects light too, but scatters it in all directions, which is why you cannot see your face in it. Light also bends when it passes into water or glass, because it travels more slowly in them. That bending is called refraction, and it makes a straw look broken at the surface of a drink.
Colour is what is left over
Why is an apple red? White light is a mixture of all the colours, as a prism shows when it spreads sunlight into a rainbow. The apple’s skin absorbs most of the colours and reflects red back to your eye. A white shirt reflects nearly all the light that hits it, while a black one absorbs nearly all of it, which is why black clothes get hotter in the sun. Put a red apple under pure blue light and it looks almost black, because there is no red light for it to reflect.
Curriculum links: NGSS MS-PS4-2