Light and how we see
Physics · Key Stage 2 · The School
Light goes straight
Light travels in STRAIGHT LINES. You can show it: line up three cards with a hole in each and you only see the lamp when all three holes are in a line. Move one card and the light is blocked. This single fact explains most of what light does at this level, including why you cannot see round a corner without a mirror.
How seeing actually works
Some objects are LUMINOUS — they give out their own light, like the Sun, a lamp or a flame. Most objects are not: they are seen because light from a source hits them and some of it REFLECTS off into your eye. So seeing a book runs lamp → book → eye. In a room with no light at all, no amount of staring will show you the book, because there is nothing to reflect.
Why shadows are that shape
A shadow appears where an object blocks light travelling in straight lines. Because the light cannot bend round the object, the missing patch has the same outline as the thing that blocked it. Move the object closer to the light and the shadow gets bigger, because it blocks a wider spread of the rays.
Punch a hole in the same spot on three cards and stand them in a line with a lamp behind. Look through: when all three holes line up you see the lamp clearly. Slide the middle card 1 cm sideways — and the lamp vanishes, even though nothing else has moved and the light is still on. Light could not bend that 1 cm to reach your eye. That single centimetre is the whole demonstration.