Download Mirrors and Lenses

Mirrors and Lenses
Chapter 13
The penultimate chapter!!!!
Mirrors
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Recall that your eyes gather light reflected off of objects
 This allows you to see the objects
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Light can reflect more than once
 Light bouncing off of you can then bounce off of a mirror
 This creates the image that you see in the surface of the mirror
 When the light rays bounce, they can change direction
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Mirrors use smooth, reflective surfaces that allow light to reflect
 Recall that this is called regular reflection
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The light from a mirror enters your eyes, from which the brain receives
signals and interprets them as the image.
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Different Mirrors use different shapes to cause images
“L-O-S-T” Art of Image Description
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L-Location
 Where the object is located
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O-Orientation
 Is the object upright or inverted
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S-Size
 Did the object get larger or smaller
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T-Type
 Real or Virtual
Plane Mirrors
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Flat, smooth mirrors
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L-The image appears as far away as the object is from the mirror
 If the object is 2m from the mirror, the image will appear 4m away
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O-The image is upright
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S-The object is the same size
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T-Virtual image
Concave Mirrors
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Mirror that curves inward (like a cave entrance)
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Concave mirrors have an optical axis
 Perpendicular line through the center of the mirror
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The curvature of the mirror causes all rays to be reflected through a focal
point
 Point on the optical axis through which light rays converge after reflecting from the
mirror
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The distance from the mirror to the focal point on the optical axis is called
the focal length
Ray Tracing-Concave Mirrors
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Easiest way:
 Start from top of object
 Draw straight line to mirror
 From where line strikes mirror, draw straight line
through focus
 2nd line: Start from top of object
 Draw straight line through focus to mirror
 Where ray hits mirror, draw straight line
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Where the 2 rays converge (meet up) draw the image
 It will be upside down and slightly smaller
Concave mirror: Object outside of the
focal length
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L-At least a little bit outside of the focal length
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O-Inverted
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S-Smaller
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T-Real
What about objects on the Focal
Point?
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No image is formed
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L-On the focal point
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O-none
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S-none
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T-none
Object between concave and focal
point.
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Causes mirror to magnify image of the object
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L-Inside focal length
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O-Upright
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S-Larger
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T-Virtual
Convex Mirrors
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A mirror that curves outward.
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Light rays diverge after striking the convex mirror
 They never meet
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Used often for security
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L-Past the focal point
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O-Upright
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S-Smaller
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T-Virtual
Convex Mirror Ray Diagram
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Focal point is on the other side
 “Behind the mirror”
 Your book has this incorrect…
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A bit different than concave mirrors
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First, draw a line parallel to the optical axis
from the top of the object
 This line will then travel through the focus
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Second, draw a line from the top of the
object to the mirror that would travel
through the focus
 Once it hits the mirror, it travels parallel to the
optical axis
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Draw the image where the lines converge
Lenses
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Come in concave and convex, just like mirrors
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Used in cameras, eyeglasses, contacts, etc.
Convex lenses
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Lens that is thicker in the middle than the edges
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Light rays are refracted so that they converge on a single point
 Focal length depends on the shape of the lens
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They type of image depends on where the object is relative to the focal
length
Concave Lenses
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Lens that is thinner in the middle
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Rays hit the lens and then diverge
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L-Anywhere in front of the lens
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O-Upright
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S-Smaller
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T-Virtual
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Used in some eyeglasses and microscopes
Eyesight and Lenses
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Light enters the eye through the cornea
 Transparent covering of the eye
 Causes light to converge through the pupil and into a convex lens called
the crystalline lens
 Focuses rays on the retina
 The retina converts the light to electrical signals that travel to the brain and
are interpreted
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Muscles in your eye can adjust the shape of the lens and allow you to
see near and far.
Vision Problems
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Astigmatism
 Irregular curvature of cornea
 Corneas are more oval than round
 Causes blurry vision at all distances
 Can be corrected with lenses
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Farsightedness
 Trouble seeing near objects clearly (eyes are focused to a distance)
 Light does not converge enough
 Corrected with convex lenses
 As people age, farsightedness becomes more common
 Lens becomes less flexible
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Nearsightedness
 Difficulty seeing at a distance
 Can be corrected with concave lenses
Uses of Mirrors and Lenses
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Telescopes use mirrors and lenses to gather a lot of light, and see distances
 Refracting telescopes use 2 convex lenses to gather and focus light
 Reflecting telescopes use mirrors to reflect gathered light.
 Some also contain lenses
 Usually reflecting telescopes are larger
 Space telescopes, such as Hubble and soon James Webb, use huge mirrors to reflect
and gather light
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Microscopes
 Use convex lenses (objective lenses and eyepiece) to magnify tiny images such as
cells
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Cameras
 Use lenses to gather light for photographs