Lenses are a part of our everyday lives (as every part of physics is!). Spectacles glasses, camera lenses, magnifying glasses, microscope eyepieces, telescope lenses and in almost everywhere!

Lenses work by refracting light. When a ray strikes the surface of the lens, it is refracted towards the normal. When the ray leaves the lens, it is refracted away from the normal.

Converging and diverging lenses

Lenses can be divided in two types:

  1. Converging lenses
  2. Diverging lenses

Converging lenses can be described by their appearance, which is fatter in the middle than at the edges. Converging lenses are used often as magnifying glasses and as burning glasses. Converging lenses always give magnified and detailed images.

Diverging lenses can also be described by their appearance, which is fatter in the edges than at the middle. Diverging lenses always give diminished images.

Focal point, focal length and principal focus

There are a few keywords that we recommend you to get familiar with.

Learning what focal point, focal length and principal focus will help you draw and understand ray diagrams involving lenses.

Focal point See principal focus
Focal length The distance from the center of the lens to its principal focus.
Principal focus The point at which rays of light parallel to the axis converge after passing through a converging lens.


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