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Mirrors
Chapter 13 - 15
Chapter 13

Section 2 & 3
Mirror History
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Mirrors are the oldest optical
instruments
Almost 4000 years ago, Egyptians
used polished metal mirrors
Sharp, well-defined reflected images
became possible in 1857, when Jean
Foucault developed a method for
coating glass with silver
Plane mirror

Light rays are reflected with equal
angles of incidence and reflection
• Bathroom mirrors

Object- a source of diverging
(spreading) light rays
• Every point on the object is a source of
diverging light
• May be luminous, more commonly
illuminated
Image
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What you see- brains thinks the light
comes from the image
Virtual image- an image where the
light rays do not actually converge
on the point
In a bathroom mirror- where do you
see the image? Is that where you
really are?
Example- On board
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If the image and the object are
pointing in the same direction, the
image is called an erect image
In a plane mirror- the image formed
is the same size as the object and is
the same distance behind the mirror
as the object is in front. If you wave
your right hand it looks like the left
hand is moving
Concave mirrors

Reflects light from the inner surface
• Inside a spoon
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The surface of a concave mirror reflects
light to a given point called the focal point
(F)
The distance from the focal point to the
mirror along the principal axis is the focal
length (f)
Concave

The concave mirror is used whenever a
magnified image of an object is needed
• Dressing-table mirror

The radius of curvature is the same as the
radius of the spherical shell of which the
mirror is part. Therefore the distance from
the mirror’s surface to the center of
curvature C is the radius.
Features of an image

Can be found using formulas, and
will tell you if the image is:
• Real or virtual
• Inverted or right side up
• Magnified or reduced
Formula symbols
di is image distance
 do is object distance
 hi is image height
 ho is object height
 f is the focal length (1/2 the radius)
 C is the center of curvature

• (2f or radius)
Equations
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On board
• 1/do + 1/di = 1/f
• M = hi/ho = - di / do
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Page 457, 458

Assignment – page 462 (1-2)
Convex Mirrors
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A spherical mirror that reflects light
from its outer surface
Rays reflected from a convex mirror
always diverge, so they do not form
real images
Form reduced images, and reflect a
larger area of view
Assignment

Page 466
• (1-2)
Chapter 14

Section 2
Lenses
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A lens is transparent with a refractive
index larger than air
Convex lens- thicker at the center
• Are converging lenses; refract parallel
light rays so that the rays meet

Concave lens- thinner in the middle
• Diverging lens; the rays passing
through are spread out
Lens/Mirror Equation
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f is positive for convex lenses and
negative for concave lenses
do is positive on the object side of
the lens
 di is positive on the image side,
where images are real
 di is negative on the object side of
the lens where images are virtual
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Equations
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The lens/Mirror equation can be used
to find the location of an image
The magnification equation can be
used to find the image size
Assignment- Page 501 (1 & 4)
How do eye glasses Work?
How do you think eye glasses work?
 How do microscopes and telescopes
work?
 What about a camera?

Write your hypothesis/explanation
for each.
 Read Page 502-505
 Were you right or wrong?
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Why are the edges of shadows not
sharp?
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Grimaldi named the slight spreading
of light around barriers diffraction
Thomas Young developed an
experiment that allowed him to make
a precise measurement of light’s
wavelength using diffraction
Young’s Double-Slit Experiment
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Young directed a beam of light at two
closely spaced narrow slits in a
barrier
The light was diffracted, and the rays
from the two slits overlapped. When
the overlapping light beams fell on a
screen a pattern of bright and dark
bands was produced
Measuring the wavelength of light
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Young used the double-slit experiment to
make the first precise measurement of the
wavelength of light
λ = (xd) / L
x = the separation between the central
bright line and the first-order bright line
L= distance between slit & screen
d = distance between the two slits
Diffraction Gratings
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Transmits or reflects light and forms
an interference pattern in the same
way that a double-slit does
Wavelength using a Diffraction
Grating
λ = (xd)/L = d sin θ
Assignment
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Page 531 (1)

Page 538 (1 & 2)
Lasers