Convex and Concave Lenses

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A lens is a block that causes light to refract and form an image.
There are two types of lens: convex and .
A convex () lens is curved outwards on both sides.
Rays from a single point on a distant object arrive at the lens to one another.
A convex lenses refracts these parallel rays so that they come together at a point called the principal .

These lenses focus the rays of light to produce a image that can be projected onto a screen.
The length is the distance between the centre of the lens and the image.

A concave (diverging) lens is curved on both sides.
Concave lenses refract the parallel rays of light so that they spread from one another.
This means that they form a image that cannot be projected onto a screen.
The diverging rays can only be seen by the , and appear as having come from a different point to where the object is.

The point at which the rays appear to have come from is called the .
The focal length is the distance between the of the lens and the focus.