Light reflects from surfaces — Physical education, 11–13 years
Seeing a mirror image is one example of reflection: light changes direction at a surface and then travels to your eyes. The angle of arrival and the angle of departure are equal.
Light bounces from a surface
When light reaches a surface, some or all of it may change direction and travel away: this is reflection. A smooth surface sends nearby rays in organised directions, so it can form a clear image. A rough surface scatters the rays, so it usually looks bright but does not act like a mirror.
Why do we need reflection?
An object is not visible to you unless light from it reaches your eyes. Reflection explains how light from a dark room, a road sign or a mirror can be redirected towards you. Measuring angles gives a reliable way to predict where the light will go instead of relying on guesswork.
Using equal angles
Draw a straight line for a mirror and a perpendicular normal line at the point where a ray arrives. If the incoming ray makes 35° with the normal, measure 35° on the other side and draw the reflected ray there. It will leave at 35° from the normal, although the two rays make a different angle with the mirror itself.
Measure from the normal
A common mistake is to measure the angle from the mirror surface, because that is the line you can see most easily. The rule uses the normal, an imaginary line at right angles to the surface. If the ray is 30° from the normal, it is 60° from the surface, so both numbers can be correct but answer different questions.
Reflection helps us see and aim
Mirrors use organised reflection to make images, while bicycle reflectors send light from headlights back towards drivers. Periscopes use several reflections so someone can see over an obstacle. Road signs are designed to reflect strongly in a useful direction, especially when car headlights strike them at night.
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