GoalSort things into light sources and things that are not light sources, even when they look bright.
New words
reflect · to bounce light off a surfaceshiny · smooth and bright, like a mirror or a metal spoonswitched on · working, with the electricity flowing
Explanation
Some things look bright, but they do not make their own light. A mirror is shiny. It can bounce light that falls on it, but it has no light of its own. We say a mirror reflects light. A metal spoon does the same. A book and a cloud are not light sources either. We can only see them when light falls on them. A lamp is only a light source when it is switched on. A lamp that is switched off gives out no light. To decide, ask yourself: does it make its own light?
Worked examples
A shiny mirror on the wall looks bright when light falls on it. But it does not make its own light, so it is not a light source.
A laptop screen makes its own light. A closed book on the desk does not.
A cloud looks white and bright in the daytime, but it is not a light source. Its light comes from the Sun.
Class activity
Dark box test (with an adult): put a mirror, a book and a spoon in a big cardboard box that has a lid. Lift the lid a tiny bit and peep in. Can you see the things in the dark? Now put a switched-on torch inside with them and peep in again. Which thing makes its own light? Which things can you only see when light from the torch falls on them?
Practice
1
Is a mirror a light source? Why or why not?
No. It only reflects light. It does not make its own light.
2
Is a lamp a light source when it is switched off?
No. It only makes light when it is switched on.
3
Which two of these make their own light?
A, the phone screen (when it is on), and C, the fire.
4
On a sunny day, a white cloud looks very bright. Where does its light come from?
From the Sun. The Sun’s light shines on the cloud. The cloud does not make its own light.
