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```					Adv Physics

Chapter 15
Section 1
Refraction

If wave strikes
boundary at a right
angle the wave
continues in a
Air            straight line since all
parts of the wave
water          slow at the same
time by the same
amount
Refraction

If wave strikes
boundary at an angle
the wave abruptly
changes direction
Air            since part of the
wave is slowed while
water          part maintains its
speed
Refraction

 Bending of a wave as it passes from one
medium to another have a different
density and a different speed
Refraction
Reflected light follows the
Inc ray           reflected     law of reflection so i = r
ray
i   r               If i > 0 degrees then the
transmitted part is
refracted

If i = 0 degrees then the
normal                        transmitted part travels
refracted       straight through and is
ray          not refracted
Refraction

If wave strikes the
boundary at an angle
the wave abruptly
changes direction
Water          since part of the
wave is sped up
air            while part maintains
its speed
Refraction
 If you travel into a medium where you slow
down, the light bends toward the normal and
the angle gets smaller
i > refraction angle
 If you travel into a medium where you speed
up, the light bends away from the normal and
the angle gets bigger
i < refraction angle
 Exception! If i = 0 degrees (travels along the
normal) the light doesn’t bend at all
Index of Refraction

 Measure of light’s speed in a medium
 Ratio of the speed of light in a vacuum to
the speed of light in a medium

n=c/v

where n = index, c = speed of light in
vacuum, v = speed of light in medium
Index of Refraction

1. Speed of light in water = 2.25 x 108 m/s
n = c/v = 3 x 108 / 2.25 x 108 = 1.333

2. Speed of light in glass = 2 x 108 m/s
n = c/v = 3 x 108 / 2 x 108 = 1.5

Note: larger the value for n, the slower
light travels in that medium
Sample Problem

The light emitted by a He-Ne laser has a
frequency of 4.74 x 1014 Hz. Find the
wavelength of the light in a vacuum and
in ordinary crown glass.
Snell’s Law
 When light travels from a
material with index n1
into a material with index
n2, the angle of
refraction, Θ2 is related    Θ1
to the angle of incidence,             n1
Θ1 by                                  n2

n1 sinΘ1 = n2 sinΘ2         Θ2
Sample Problem

A ray of light passes from air into water,
striking at an angle of 25 degrees with
the normal. The index of refraction of
water is 1.333. Calculate the angle of
refraction of the ray of light.
Sample Problem

A light ray strikes an air/water surface at an
angle of 46 degrees with respect to the
normal. Find the angle of refraction
when the direction of the ray is a) from air
to water and b) from water to air.
Sample Problem

A light ray is incident on the outer surface
of the cornea at an angle of 40 degrees
with the normal. Find the angle the
transmitted ray makes with the normal.
Sample Problem

A light ray passes from water into ice. If
the transmitted ray makes an angle of 20
degrees with the normal, what is the
angle of incidence.
Sample Problem

Light travels from air through a flat sheet of
glass ( n = 1.5 ) into water. If the angle of
incidence in air is 30 degrees, what is the
angle of the refracted ray in water?
Sample Problem

A light ray travels from air to water and
then is reflected by a mirror under water.
It strikes the mirror at an angle of 30
degrees. A) Find the angle of incidence
as the ray enters the water. B) Find the
angle of refraction as the ray leaves the
water.

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Jun Wang Dr
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