Lenses & Images
A lens or mirror can bend rays of light to make an image.
There are two different kinds of lenses: converging and diverging. Mirrors follow the
There are two different kinds of images: real and virtual. Optical devices that you look
through use virtual images; those that project images use real images.
Converging & Diverging Lenses
f (focal length) is +
Parallel rays are converged at the focal point, beyond the lens
Rays continue after passing through the focal point.
f is –
Focal point is in front of the lens
Rays appear to diverge from the focal point.
P = 1/f
Unit for refractive power is the diopter
1 D = 1 m
What is the power of a converging lens with focal length 20 cm?
1/0.2 m = 5 diopters
What is the power of a diverging lens of focal length -20 cm?
For two lenses in close proximity, P total P 1 P 2 A converging lens has a focal length of 10 cm is plac