Reflection
How can a mirror show you your own face?
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Explain
Light bounces off mirrors.
That is how you see yourself.
Reflection is light bouncing off a surface. A smooth, shiny mirror bounces it very neatly.
We see most things because light bounces off them and into our eyes.
Change the angle. Light leaves a mirror at the same angle that it arrived.
Law of reflection: the angle of reflection equals the angle of incidence.
Both angles are measured from the normal, an imaginary line at right angles to the surface.
Rough surfaces scatter light in all directions, which is called diffuse reflection.
- Light hits the mirror
- It bounces off
- Angles match
Want the full story?
Each tiny part of a rough surface still obeys the law, but the surface points in lots of directions. Your image in a flat mirror looks as far behind the mirror as you are in front of it.
The Formula
angle of reflection = angle of incidence
- the angle of the incoming ray, from the normal line, measured in degrees (°)
- the angle of the reflected ray, from the normal line, measured in degrees (°)
Try the numbers
Angle out: 40°
Try it at home
Ask a grown-up to help
You need a small mirror, a torch, paper.
You need: a small mirror, a torch, paper.
Wave at a mirror. It waves back!
- Stand a mirror on paper.
- Shine a thin torch beam at it.
- Mark the two paths of the beam, and compare the angles.
What's happening: the angle going in matches the angle coming out.
Physics is life
Your body
Your eyes see reflected light.
Daily life
Cars have mirrors.
Nature
Still lakes act like mirrors.
Space
The Moon shines with sunlight.
Quick check
Question 1 of 3
Words to know
Reflection: Light or sound bouncing off a surface.
- Reflection
- Light or sound bouncing off a surface.
- Normal line
- An imaginary line at right angles to a surface.
- Light
- Energy that travels as waves you can see.