Lenses

Applications of Light Refraction• What are some common

applications of the refraction of light?

• Cameras• Microscopes• Lenses• Eyeglasses• Human eye• Telescopes• Binoculars

Lenses

• Definition: curved piece of glass• When light passes through as lens,

direction of light changes• Each light ray strikes surface of lens at

slightly different angle• Two types: 1) Converging lens:

– Bends light inward– Ex: magnifying glass

2) Diverging lens:– Bends light outward

Lenses

• Compound microscope uses multiple lenses to magnify an object

• Magnification: any change in the size of an image compared with the size of the object

The Human Eye

• Without refraction, we couldn’t see at all!• Human eye works similar to a camera

Camera vs. Human Eye

• Light enters through large lens

• Lens focuses light• Light creates image

on film at back of camera

• Light enters eye through cornea (transparent tissue)

• Light passes through pupil (hole in iris)

• Light travels though lens which focuses image on retina (back layer of eye)

The Anatomy of the Human Eye

• Cornea:– Where light first enters

eye– Responsible for 70% of

refraction of light in eye

• Lens:– Curvature determines

refraction of light– Muscles adjust curvature

of lens

The Anatomy of the

Human Eye

• Retina:– Made up of light sensitive cells, rods and cones

• When light strikes rods and cones, signals sent to brain where they are interpreted as images

– Cones: responsible for color vision• Only respond to bright light• Why we can’t see color in very dim light

– Rods: sensitive to dim light• Can’t resolve details well

Eye Defects

• Near-sightedness (also called myopia)

• Common cause of blurred vision

• Objects in the distance appear blurry and out of focus

• Caused by change in the shape of the eyeball that makes the eyeball oval (egg-shaped) rather than round

Near-Sightedness• Causes light rays entering the eye to focus in

front of retina

Far-Sightedness

• Also called hyperopia

• Can clearly see objects that are far away, but they have trouble seeing objects up close

• Occurs when eye is too short lengthwise

• This causes an image to focus behind the retina

Far-Sightedness

Concave Lens vs. Convex Lens

• Convex: bends light inward

• Concave: bends light outward

Lenses can be used to correct vision defects

• Near-sightedness (right) Concave lens• Far-sightedness (left) Convex lens