Resource 3: Information on light
Background information / subject knowledge for teacher
Sources of light
- The sun – major source of light and heat here on Earth.
- Stars – distant suns. We can just see the light of these but don’t feel the heat.
- The moon and planets – reflect the light of the sun.
- Lightening flashes during thunderstorms.
- Fire, flames, sparks, heated metals and glowing embers.
- Electric lights.
- When white light is refracted (bent) by certain transparent surfaces, even raindrops, it is split and reveals the seven colours of the rainbow.
- Coloured things absorb all the other colours but reflect their own colour. So a red car reflects only red light, red glass in a car’s brake light transmits only red light.
- Nothing travels faster than light.
- Like sound, light travels as waves of energy. We talk of sound waves, but light ‘rays’ or ‘beams’ of light.
- Light rays generally travel in straight lines that radiate out from a source.
- We see things because light rays bounce off them (get reflected).
- Darkness is because of an absence of light. If there is no source of light to reflect off things we get blackness and cannot see anything.
What happens to travelling light?
- It passes straight through transparent things (glass, water, clear plastic, etc.).
- It partly passes through translucent things (wax paper, tissue, tinted or frosted glass, mist and clouds, etc.).
- Light is blocked by opaque things – this causes shade and shadows.
- Light is also reflected by opaque things.
- Very shiny surfaces (mirrors, polished metal etc.) reflect a clear image/picture.
- Dull surfaces scatter the light that they reflect.
- When light is neither transmitted or reflected, it is absorbed.
- When all the light is absorbed by anything we see it as black.
- When we look into a mirror, the image we see seems to come from behind the mirror.
- A mirror image turns things otherwise (lateral inversion). That is why we can’t easily read a page held up to a mirror.
- Try to shake hands with your own image in a mirror – you will see that as you hold out your right hand, the mirror image ‘holds out’ its apparent left hand.