Different Images Produce Different Kinds of Images
Lenses form images by refracting light and changing its direction. There are two main types of lenses converging and diverging.
They have different shapes and have opposite effects on the light rays.

1. A converging lens is convex - it bulges outwards.
It causes parallel rays of light to converge (move together) at the principal focus
2. A diverging lens is concave - it caves inwards.
It causes the parallel rays of light to diverge (spread out)
3. The axis of the lens a line passing through the middle of the lens
4. The principal focus of a converging lens is where rays hitting the lens parallel to the axis meet
4. The principal focus of a diverging lens is the point where the rays hitting the lens parallel to the axis appear to all come from - you can trace them back until they appear to meet up at the point behind the lens.

There are THREE Rules for Refraction in CONVERGING Lenses...

An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side

An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries in the same direction

There are THREE Rules for Refraction in DIVERGING Lenses...

An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus (so it appears to come from a principal focus)
An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries on in the same direction

Lenses can Produce Real or Virtual Images
1. A real image is where the light from an object comes together to form an image on a 'screen' - like the image formed on an eye's retina (the screen on the back of the eye)
2. A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place
You can get a virtual image from a magnifying glass - the image looks bigger than the object actually is

To describe an image properly, you need to say three things:

How big it is compared to the object
Whether it is upright of inverted relative to the object
Whether it's real or virtual

	Created by Amula over 10 years ago

GCSE Physics Note on Lenses and Images , created by Amula on 24/02/2014.