Light reflects from surfaces — Physics, 11–13 years
Reflection is what happens when light bounces from a surface into our eyes, allowing us to see objects and images.
Idea
Light usually travels in straight lines until it meets something. At a surface, some light can bounce away instead of passing through or being absorbed; this is reflection. A smooth mirror sends the light in an orderly direction, while paper or a wall scatters it in many directions.
Why
We need reflection to explain why a dark room becomes visible when a lamp is switched on. Objects do not usually make their own visible light; they reflect some light from a source towards our eyes. Studying reflection also explains why a mirror can form a clear image while a painted wall normally cannot.
Worked example
Imagine a small torch pointing at a mirror. Step 1: draw the normal, an imaginary line at 90° to the mirror. Step 2: if the torch beam arrives 30° from the normal, the reflected beam leaves at 30° on the other side. Step 3: move your eye into that reflected path and you can see the bright spot; move away and it disappears.
Common trap
A reasonable mistake is to think that a mirror turns light straight back, whatever its angle. That seems true when you stand directly in front of it, because the incoming and outgoing paths line up. In fact, the light leaves at the same angle as it arrived, measured from the normal, so changing the torch or your position changes what you see.
In the world
Car headlights and bicycle reflectors use carefully shaped surfaces to send light where drivers can notice it. Periscopes use mirrors to let someone see over an obstacle or around a corner. In buildings, shiny surfaces can make a room brighter, while rough surfaces reduce sharp glare by scattering light.
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