Reflection and how mirrors work
Physics · Key Stage 2 · The School
The rule of reflection
Light bounces off a surface at the same angle it arrived — the angle in equals the angle out, measured from a line at right angles to the surface. Because light travels in straight lines, that single rule predicts exactly where a reflected ray goes, and it is what lets a periscope see over a wall using two angled mirrors.
What a mirror image is like
A mirror image is the same size and the same distance behind the glass as the object is in front, but LEFT AND RIGHT ARE SWAPPED. That is why writing held to a mirror is unreadable and why an ambulance has AMBULANCE reversed on its bonnet, so a driver reads it correctly in the rear-view mirror.
Why paper is not a mirror
A mirror is smooth, so parallel rays arriving stay parallel when they leave and the image survives. Paper looks smooth but is rough at a small scale, so rays scatter in every direction — you still see the paper, but no image forms. The difference between a mirror and a wall is not what they are made of but how smooth they are.
Stand 1 m from a mirror and ask a friend to guess how far away your image looks. It looks 2 m away — 1 m to the glass and 1 m behind it. Test it: hold a book at arm's length and focus a phone camera on the book, then on your reflection. The camera has to refocus, because the image is genuinely further away than the glass. Step back another metre and the image retreats two.