AQA GCSE Physics

Revision Notes

6.3.1 Convex & Concave Lenses

Convex & Concave Lenses

  • 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

Lens focus, IGCSE & GCSE Physics revision notes

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

Diverging Lens, downloadable IGCSE & GCSE Physics revision notes

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:

convex-concave-symbols, IGCSE & GCSE Physics revision notes

Concave and convex symbols

Exam Tip

Make sure you remember the symbol for each type of lens, 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

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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