Chapter 26 The Refraction of Light: Lenses and Optical Instruments.
Lenses. Applications of Light Refraction What are some common applications of the refraction of...
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Transcript of Lenses. Applications of Light Refraction What are some common applications of the refraction of...
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