Lecture series for Conceptual Physics, 8th Ed'

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Lecture series for Conceptual Physics, 8th Ed.
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Reflection p486
Tuning forks are to sound as electrons are to
photons.
The surface electrons of a page in the book
reflect all the colors and appear to be white.
The black letters absorb all the colors.
Principle of Least Time p487
Pierre de Fermat, 1650, said,
Out of all possible paths that light might take
to get from one point to another, it takes the
path that requires the shortest time.
This concept underlies all the formulas that
describe light paths.
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Law of Reflection p487
How does light get from A to the mirror and to B?
Two possible paths
But, how do we find the least time?
Try this construction
In fact, it works in all cases.
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More reflections
The angle of incidence equals the angle of
reflection.
The reflected rays seem to come from a point
behind the mirror.
This is a virtual image.
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Plane Mirrors p489
Does a mirror shift left and right?
NO!
Front and back are switched.
back
front
If your nose is closest to the mirror in front,
then its image is also closest to the mirror in
back.
Smaller image in a convex mirror.
Larger image in a concave mirror.
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Focal point
axis
object
Virtual image
Convex mirror
object
axis
Virtual image
Concave mirror
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Diffuse Reflection p490
A radio telescope
Rough to light.
Polished to radio waves.
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Refraction p492
Light bends when it changes speed at an interface.
Youre the lifeguard. Which path takes the least
timedashed or solid?
Remember that you can run faster in the sand than
you can swim.
The dashed line takes the least time.
The relative sizes of the angles depend on the
difference in speed.
The index of refraction, n, is used.
speed of light in a vacuum
n
speed of light in the material
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From air through glass
The path of least time.
A to B is perpendicular to the interfaceno
refraction.
A to Q hits glass and bends.
Q to C continues through glass and bends as it
emerges.
C to C continuesparallel to AQ but offset.
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Light goes through these shapes always taking the
least time.
The index of refraction, n, for air is nearly 1,
but
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Mirages
Cyclist sees blue sky where the road should be.
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Cause of Refraction p496
Snells Law
N1 sinO1 n2 sinO2
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When light enters a denser medium (the speed of
light is slower), the light bends toward the
normal.
And, vice versa.
The reflection is normal The angle of
incidence equals the angle of reflection.
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Dispersion p497
Higher frequency light is closer to the resonance
frequency of glass electrons.
So, light at the blue end of the visible spectrum
refracts more than light at the red end of the
visible spectrum.
This is why prisms make rainbows.
And, its why focal points of lenses get fuzzy
when blue light is focused closer to the lens
than red light.
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Rainbows p498
Stand with your back to the sun and image an arc
of 42oC.
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Total Internal Reflection p502
Note the critical angle 43o
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Heres the critical angle from under water.
Total internal reflection causes 100 of the
light to bendno loss.
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More on Total Internal Reflection p503
This concept is used in binoculars
The critical angle for a diamond is24.5oC
Fiber optics depend on total internal reflection.
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Lenses p505
A converging lens
A diverging lens
Important features of a lens.
Where do the red rays bend?
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Surface ripples on a pond create familiar
patterns of light on the bottom.
Image Formation by a Lens p506
Lenses make images
No image.
Pin-hole camera
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Lens Defects p509
Light passing through edge of lens focuses in
front of light passing through middle of lens.
1. Cover the edges.
Cures
2. Combine concave and convex lenses.
Blue light is refracted more than red.
Combining different types of glass usually cures
this.