Reflection

Images and mirrors

Lateral inversion

When you look at yourself in a mirror what you see is an image of yourself. The light appears to come from the image. The light, however, travels from you to the mirror and is then reflected back towards you from the surface of the mirror. There is nothing behind the mirror. You will have noticed that your image appears to be reversed from left to right. If you raise your right hand, the image in the mirror raises what would be its left hand if it was real person facing you.

Our brain is used to seeing things back-to-front in a mirror, and we take it for granted. However, if you are suddenly forced to perform a task while looking in a mirror, it can be difficult until your brain adapts and learns how to cope.

What is causing the back-to-front effect is called lateral inversion.

Real and virtual images

When light is reflected off a curved mirror it can produce an image in two different ways.

1. The mirror can reflect the light onto a screen (or piece of paper) and make an image on that screen. The image you see this way is usually upside down. It is also in full colour and the image is probably smaller than the real thing.
   An image that can be seen on a screen is called a real image.


2. The mirror can reflect the light into your eyes and you see the image in the mirror instead of on a screen. This image is usually the right way up. The size of the image can be bigger than the real thing like in a make-up mirror, or it can be smaller than the real thing like in a shop security mirror. The image may be the same size as the real thing as in the plane mirror in the bathroom. The image is in full colour.
   An image that can be seen in a mirror is called a virtual image.

The virtual image formed in a plane mirror is the same distance behind the mirror as the object is in front of the mirror. This means that when you look at yourself in a flat mirror your image seems to be just as far behind the mirror as you are in front of it.

Law of reflection

The light rays that hit the surface of a mirror are called the incident rays. The light rays that are reflected from the mirror are called the reflected rays. The normal is a word used to name the line that is drawn at right angles to the surface of the mirror at the point where the light ray is reflected. When a light ray is reflected off the surface of a mirror the angle of incidence always equals the angle of reflection. This is called the Law of reflection.

Structure of mirrors

Most mirrors are made of a silvered layer on the back surface of glass. This means the light rays must pass through the glass twice as it is reflected. This can be a disadvantage because if the glass is imperfect, it will affect the image seen in the mirror.

It is possible to silver the front surface of the mirror glass. This means the light is reflected without having to pass through the glass. However, there are disadvantages to having the silvered surface exposed. It can easily be scratched and can tarnish with age.

Uses of reflection

Convex mirrors are often used in shops as security mirrors because of the type of image produced by that mirror. The image is smaller but shows a wide angle view of the shop.

Concave mirrors are often used in torch lights or in the headlights of cars. The light travels in all directions from the light globe towards the mirror behind it. The rays are then reflected by the mirror and they form a beam of light (a bundle of parallel rays).