# Reflection

All waves bounce off surfaces. Water waves hit walls and bounce off them, light hits mirrors and bounces off and so on. We can imagine the direction of the wave travel to be a streak, drawn as a straight line with a pencil. It will strike a surface then rebound at the same angle as it struck.

We never use words like ‘bounce off’ or ‘rebound’. Instead, we say that

The incident ray is reflected at the surface at an angle θ to the NORMAL (an imaginary line perpendicular to the surface) so that the angle of incidence equals the angle of reflection.

Also the incident ray, the normal and the reflected ray can all be drawn on the same flat sheet.

Here’s a little animation to show you…

An image in a mirror isn’t real. Someone could walk behind the mirror and the image in it would still be there.  This kind of image is called a virtual image, because it hasn’t been formed by real rays of light which meet at it. If you stand 1m away from a mirror, how far behind the mirror is your image?  Look in a mirror and wink at yourself. What do you notice? Hold up some writing in front of a mirror. What do you notice?

Now for the physics bits…For light (an electromagnetic radiation) a flat shiny surface, like a plane (flat) mirror, is a good reflector. Unlike the ‘hall of mirrors – above- a plane mirror is one which is straight and not curved so the image appears to be the same distance behind the mirror as the real object is in front of it. This is because the brain thinks that light travels in straight lines without changing direction.

we can see that angle i= angle r

The wavelength, frequency and speed is unaffected by the reflection.

Finally, the image is the same size and colour as the object.

Thanks to Apple Computers for a screenshot of their iMac wallpaper