Convex & Concave Lenses (AQA GCSE Physics)

• A lens is a piece of equipment that forms an image by refracting light
• There are two types of lens:
  • Convex
  • Concave

Convex Lenses

• In a convex lens, parallel rays of light are brought to a focus
  • This point is called the principal focus

• 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

The focal length is the distance from the lens to the principal focus

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

Parallel rays from a concave lens appear to come from the principal focus

Representing Lenses

• In diagrams, the following symbols are often used to represent each type of lens:

Concave and convex symbols