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