Reflection and Refraction

Waves – Topic 4
Chapters 26
Reflection & Refraction
Law of Reflection
– The angle of
incidence equals
the angle of
The incident and
reflected rays lie in
the same plane
with the normal.
Image position
 You
think in
 The
image is
behind the
Diffuse vs Specular
Diffuse Reflection
– Light incident upon
a rough surface
– Law of reflection
still holds; Normals
are not parallel.
Specular Reflection
– Mirror like reflection
– All Normals are
Sudden change in direction of a wave as
it changes speed.
– It must enter obliquely to change direction!
Which direction does it bend as it slows?
In both cases the speed of the wave has
decreased. This is indicated by the
decrease in wavelength!
 In
which medium does light travel
faster? (glass rod appears bent)
Speed of light
n is the absolute index
of refraction. This is a
measure of optical
density. n is defined
as the ratio of the
speed of light in a
vacuum to the speed
of light in a new
v is the speed of light
in the new medium.
c= 3.0 x 108 m/s
As the index increases
the speed decrease.
Draw a graph for
index vs. speed.
Relative Index of Refraction
n is the relative index of
refraction. If air is not
used, then remember
nrel = n2/n1
What is the relative index
when going from
diamond into lucite?
If nrel < 1 ;
speeds up
If nrel > 1 ;
slows down
n(water)=1.33; n(glass)=1.50; n(air)=1.00
Calculate the
speed of light in
water and glass.
Vw = 2.26 x 108m/s
Vg = 2.00 x 108m/s
n1- from
n2 - into
When a wave slows down it bends closer to the
normal. {less to more – toward} n2>n1
When a wave speed up it bends away from the
normal. {BLA – Big ―› Little – Away} n2<n1
If light rays bend closer to the normal
when slowing down, why does the glass
rod seem to bend away form the normal?
Apparent Depth
R – Real Depth
A – Apparent Depth
Diverging rays
enter your eyes.
You “think” in
Straight Lines.
A virtual image
appears to come
from point y
Apparent Depth
 If
the chest is 20 m below the
surface at what depth will the image
appear? Assume nsea water = 1.34
Snell’s Law
n1sinθ1 = n2sin θ2
v1/v2 = λ1 / λ2
A monochromatic light ray f= 5.09 x 1014 Hz
is incident on medium X at 55˚. The
absolute index of refraction for material X
is 1.66
What is material X?
Determine the angle
of refraction.
Determine the
speed of light in
medium X.
Ex: Solution
The index of 1.66 is Flint Glass
To find the angle of
refraction use
Snell’s Law.
θ2= 30˚
To find the speed use
v = 1.8 x 108 m/s
 The
breaking up of white light into its
component frequencies.
Refractive & Frequency
The refractive index
depends on the
medium & the
frequency of light.
Each frequency
“color” propagates at
a different speed and
bends a different
Critical Angles
 Def:
The angle of incidence when the
angle of refraction is 90 degrees.
 Only
exist when you have the BLA’s
– Big to Little Away
 When
a light ray exceeds the critical
angle it undergoes total internal
reflection (TIR)
Snell’s Law Lab
 What
factors effect the index of
refraction of a liquid?
 Write up a planning A and B for this
question. (Last IB Assessment)
 Research any procedures you might
want to use when investigating.
– I may modify your methods based on
materials we have available.