Lenses (Oxford AQA IGCSE Physics)
Revision Note
Convex Lenses
A lens is a piece of equipment that forms an image by refracting light
There are two types of lenses:
Convex
Concave
In a convex lens, parallel rays of light are brought to a focus
This point is called the principal focus (sometimes referred to as the focal point)
This lens is sometimes referred to as a converging lens
The distance from the lens to the principal focus is called the focal length
This depends on how curved the lens is
The more curved the lens, the shorter the focal length
Light rays passing through a converging lens
Concave Lenses
In a concave lens, parallel rays of light are made to diverge (spread out) from a point
This lens is sometimes referred to as a diverging lens
The principal focus is now the point from which the rays appear to diverge from
Light rays passing through a diverging lens
Representing Lenses
In diagrams, the following symbols are often used to represent each type of lens:
Representing convex and concave lenses
Examiner Tip
Remember the symbol for each lens type, as you will be expected to draw these for ray diagrams in your exam!
To remember which lens is converging or diverging, think of the following: Convex lens = Converging
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