Lenses (Oxford AQA IGCSE Physics)

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