Types of lens
When light is Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. it changes direction due to the change in density as it moves from air into glass or plastic.
Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses.
A lens can be converging (convex) or diverging (concave).
Converging (or convex) lenses
A converging lens is thicker in the middle than it is at the edges.
Parallel light rays that enter the lens converge.
They come together at a point on the principal axis called the principal focus F.
The centre of the lens is called the optical centre C.
A ray of light incident at the optical centre passes straight through without being bent.
In a ray diagram, a converging lens is drawn as a vertical line with outward facing arrows to indicate the shape of the lens.
Key point
- The focal length f of a converging lens is the distance between the optical centre, C, of the lens and the principal focus, F.
- Focal length is measured in m, cm or mm.