Reflection and Refraction

1. Waves – Topic 4Waves – Topic 4
Chapters 26Chapters 26
Reflection & RefractionReflection & Refraction

2. ReflectionReflection
 Law of ReflectionLaw of Reflection
– The angle ofThe angle of
incidence equalsincidence equals
the angle ofthe angle of
reflectionreflection
 The incident andThe incident and
reflected rays lie inreflected rays lie in
the same planethe same plane
with the normal.with the normal.

3. Image positionImage position
 You think inYou think in
straightstraight
lines!lines!
 The image isThe image is
locatedlocated
behind thebehind the
mirror.mirror.

4. Diffuse vs SpecularDiffuse vs Specular
ReflectionReflection
 Diffuse ReflectionDiffuse Reflection
– Light incident uponLight incident upon
a rough surfacea rough surface
– Law of reflectionLaw of reflection
still holds; Normalsstill holds; Normals
are not parallel.are not parallel.
 Specular ReflectionSpecular Reflection
– Mirror like reflectionMirror like reflection
– All Normals areAll Normals are
parallelparallel

5. RefractionRefraction
 Sudden change in direction of a wave asSudden change in direction of a wave as
it changes speed.it changes speed.
– It must enter obliquely to change direction!It must enter obliquely to change direction!
 Which direction does it bend as it slows?Which direction does it bend as it slows?

6. RefractionRefraction
 In both cases the speed of the wave hasIn both cases the speed of the wave has
decreased. This is indicated by thedecreased. This is indicated by the
decrease in wavelength!decrease in wavelength!

7. RefractionRefraction
 In which medium does light travelIn which medium does light travel
faster? (glass rod appears bent)faster? (glass rod appears bent)

8. Speed of lightSpeed of light
 v is the speed of lightv is the speed of light
in the new medium.in the new medium.
 c= 3.0 x 10c= 3.0 x 1088
m/sm/s
 As the index increasesAs the index increases
the speed decrease.the speed decrease.
 Draw a graph forDraw a graph for
index vs. speed.index vs. speed.
nn is the absolute indexis the absolute index
of refraction. This is aof refraction. This is a
measure of opticalmeasure of optical
density.density. nn is definedis defined
as the ratio of theas the ratio of the
speed of light in aspeed of light in a
vacuum to the speedvacuum to the speed
of light in a newof light in a new
medium.medium.

9. Relative Index of RefractionRelative Index of Refraction
 n is the relative index ofn is the relative index of
refraction. If air is notrefraction. If air is not
used, then rememberused, then remember
 nnrelrel = n= n22/n/n11
 What is the relative indexWhat is the relative index
when goingwhen going fromfrom
diamonddiamond intointo lucite?lucite?
 If nIf nrelrel < 1 ;< 1 ;
speeds upspeeds up
 If nIf nrelrel > 1 ;> 1 ;
slows downslows down

10. RefractionRefraction
VVww = 2.26 x 10= 2.26 x 1088
m/sm/s
VVgg = 2.00 x 10= 2.00 x 1088
m/sm/s
Calculate theCalculate the
speed of light inspeed of light in
water and glass.water and glass.
nn(water)(water)=1.33; n=1.33; n(glass)(glass)=1.50; n=1.50; n(air)(air)=1.00=1.00

11. RefractionRefraction
 When a wave slows down it bends closer to theWhen a wave slows down it bends closer to the
normal. {less to more – toward} n2>n1normal. {less to more – toward} n2>n1
 When a wave speed up it bends away from theWhen a wave speed up it bends away from the
normal. {BLA – Big ―› Little – Away} n2<n1normal. {BLA – Big ―› Little – Away} n2<n1
nn11- from- from
nn22 - into- into

12. RefractionRefraction
 If light rays bend closer to the normalIf light rays bend closer to the normal
when slowing down, why does the glasswhen slowing down, why does the glass
rod seem to bend away form the normal?rod seem to bend away form the normal?

13. Apparent DepthApparent Depth
 Diverging raysDiverging rays
enter your eyes.enter your eyes.
 You “think” inYou “think” in
Straight Lines.Straight Lines.
 A virtual imageA virtual image
appears to comeappears to come
from pointfrom point yy
R – Real Depth
A – Apparent Depth

14. Apparent DepthApparent Depth
 If the chest is 20 m below theIf the chest is 20 m below the
surface at what depth will the imagesurface at what depth will the image
appear? Assume nappear? Assume nsea watersea water = 1.34= 1.34

15. Snell’s LawSnell’s Law
 nn11sinsinθθ11 = n= n22sinsin θθ22
 vv11/v/v22 == λλ11 // λλ22

16. ExampleExample
A monochromatic light ray f= 5.09 x 10A monochromatic light ray f= 5.09 x 101414
HzHz
is incident on medium X at 55˚. Theis incident on medium X at 55˚. The
absolute index of refraction for material Xabsolute index of refraction for material X
is 1.66is 1.66
1.1. What is material X?What is material X?
2.2. Determine the angleDetermine the angle
of refraction.of refraction.
3.3. Determine theDetermine the
speed of light inspeed of light in
medium X.medium X.

17. Ex: SolutionEx: Solution
The index of 1.66 is Flint GlassThe index of 1.66 is Flint Glass
To find the angle ofTo find the angle of
refraction userefraction use
Snell’s Law.Snell’s Law.
θθ22= 30˚= 30˚
To find the speed useTo find the speed use
n=c/v.n=c/v.
v = 1.8 x 10v = 1.8 x 1088
m/sm/s

18. DispersionDispersion
 The breaking up of white light into itsThe breaking up of white light into its
component frequencies.component frequencies.

19. Refractive & FrequencyRefractive & Frequency
 The refractive indexThe refractive index
depends on thedepends on the
medium & themedium & the
frequency of light.frequency of light.
 Each frequencyEach frequency
“color” propagates at“color” propagates at
a different speed anda different speed and
bends a differentbends a different
amount.amount.

20. Critical AnglesCritical Angles
 Def: The angle of incidence when theDef: The angle of incidence when the
angle of refraction is 90 degrees.angle of refraction is 90 degrees.
 Only exist when you have the BLA’sOnly exist when you have the BLA’s
– Big to Little AwayBig to Little Away
 When a light ray exceeds the criticalWhen a light ray exceeds the critical
angle it undergoes total internalangle it undergoes total internal
reflection (TIR)reflection (TIR)

21. Snell’s Law LabSnell’s Law Lab
 What factors effect the index ofWhat factors effect the index of
refraction of a liquid?refraction of a liquid?
 Write up a planning A and B for thisWrite up a planning A and B for this
question. (Last IB Assessment)question. (Last IB Assessment)
 Research any procedures you mightResearch any procedures you might
want to use when investigating.want to use when investigating.
– I may modify your methods based onI may modify your methods based on
materials we have available.materials we have available.