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Transcript of Light and Electromagnetic Radiation – Part 1 To accompany Pearson Physics PowerPoint Presentation...
Light and Electromagnetic Light and Electromagnetic Radiation – Part 1Radiation – Part 1
To accompany To accompany Pearson Pearson PhysicsPhysics
PowerPoint Presentation by R. [email protected]
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 1
Light is one form of electromagnetic Light is one form of electromagnetic radiation, EMRradiation, EMR
Quick Lab 13-1 page 635Quick Lab 13-1 page 635
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
EMREMR is radiant energy produced and is radiant energy produced and transmitted by oscillating electric and magnetic transmitted by oscillating electric and magnetic fieldsfields
All forms of EMR travel at the same speed, All forms of EMR travel at the same speed, 3.00 x 103.00 x 1088 m/s in vacuum ( m/s in vacuum (exactlyexactly 299792458 m/s)299792458 m/s)
Speed of light in vacuum: Speed of light in vacuum: cc
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 1
Light is one form of electromagnetic Light is one form of electromagnetic radiation, EMRradiation, EMR
Quick Lab 13-1 page 635Quick Lab 13-1 page 635
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Types of EMR: radio waves, microwaves, Types of EMR: radio waves, microwaves, infrared light, visible light, ultraviolet infrared light, visible light, ultraviolet light, X-rays, and gamma (light, X-rays, and gamma (γγ) rays) rays
The complete range of EMR in terms of The complete range of EMR in terms of frequency or wavelength is called the frequency or wavelength is called the electromagnetic spectrumelectromagnetic spectrum
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Figure 13.4 on page 637 is a chart of the Figure 13.4 on page 637 is a chart of the electromagnetic spectrumelectromagnetic spectrum
Table 13.1 on page 638 is a summary of Table 13.1 on page 638 is a summary of the characteristics of each region of the the characteristics of each region of the spectrumspectrum
You need to know the order of the You need to know the order of the spectrum (I suggest from lowest spectrum (I suggest from lowest frequency to highest)frequency to highest)
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Unnecessary to know numbers except Unnecessary to know numbers except the boundaries of visible: 700 nm (red) the boundaries of visible: 700 nm (red) to 400 nm (violet)to 400 nm (violet)
Also know the order of the visible Also know the order of the visible spectrum – ROY G BIVspectrum – ROY G BIV
Using the universal wave equation:Using the universal wave equation:
You can convert wavelength to You can convert wavelength to frequencyfrequency
c f
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Note that Note that visible is visible is just a tiny just a tiny part of the part of the spectrumspectrum
DiscussDiscuss spectrum spectrum regionsregions
p. 638p. 638
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
How does light travel:How does light travel:
Newton – 1704 – Light is a particleNewton – 1704 – Light is a particle
Huygens – mid 1600’s – Light is a waveHuygens – mid 1600’s – Light is a wave
Supports:Supports:
Young – 1801 – double slit experimentYoung – 1801 – double slit experiment
Fresnel – 1818 – mathematical wave theoryFresnel – 1818 – mathematical wave theory
Arago – 1818 – observation of Poisson’s Arago – 1818 – observation of Poisson’s Bright SpotBright Spot
Fizeau – 1851 – light slower in water than Fizeau – 1851 – light slower in water than airair
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Double-slit experiment: Double-slit experiment: observed!
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
End of 1800’s – physicists convinced that End of 1800’s – physicists convinced that light was a wavelight was a wave
1900 – Planck – black body radiation 1900 – Planck – black body radiation theory involving quantized energytheory involving quantized energy
1905 – Einstein – explanation of 1905 – Einstein – explanation of Photoelectric Effect using quantized light Photoelectric Effect using quantized light energyenergy
Light has both wave and particle properties
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Maxwell’s Theory of Electromagnetism:Maxwell’s Theory of Electromagnetism:
•• Recall from last unit – changing magnetic Recall from last unit – changing magnetic field across a conductor produces a current field across a conductor produces a current in a conductorin a conductor
•• current in a wire produces a magnetic field current in a wire produces a magnetic field around the wirearound the wire
Maxwell added to these:Maxwell added to these:
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
•• a changing electric field in space produces a changing electric field in space produces a changing magnetic fielda changing magnetic field
•• a changing magnetic field in space a changing magnetic field in space produces a changing electric fieldproduces a changing electric field
This led to the idea of a wave propagated by changing electric and magnetic fields
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Propagation of Maxwell’s electromagnetic waves:
Maxwell also predicted the speed of the waves and that they would behave as light – interference, diffraction, refraction, polarization
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Hertz – verification of existence of Hertz – verification of existence of electromagnetic waveselectromagnetic waves
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Demos of a Hertz-like experimentDemos of a Hertz-like experiment
AM and FM radio wavesAM and FM radio waves
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.1 What is EMR?13.1 What is EMR?
Read Read Then, Now and FutureThen, Now and Future page 646 page 646
Check and ReflectCheck and Reflect page 647 – discuss 3, page 647 – discuss 3, 4, 5, 6, 8, 11, 14, 154, 5, 6, 8, 11, 14, 15
Read pages 639-40
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.2 The Speed of EMR13.2 The Speed of EMR
Early attempt: Galileo (early 1600’s) – Early attempt: Galileo (early 1600’s) – unsuccessfulunsuccessful
First successful attempt: Huygens and First successful attempt: Huygens and Rømer (late 1600’s)Rømer (late 1600’s)
eclipse 22 minutes later here than there
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.2 The Speed of EMR13.2 The Speed of EMR
Fizeau, 1848, first successful Fizeau, 1848, first successful measurement of speed of light on measurement of speed of light on surface of planetsurface of planet
Fizeau, 1851, speed of light in water and Fizeau, 1851, speed of light in water and comparison of speed of light in water comparison of speed of light in water moving in different directionsmoving in different directions
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.2 The Speed of EMR13.2 The Speed of EMR
Michelson’s method – 1905 (awarded Michelson’s method – 1905 (awarded Nobel prize for this)Nobel prize for this)
Example: Practice Problem 3, page 650
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.2 The Speed of EMR13.2 The Speed of EMR
Practice Problem 3Practice Problem 3, page 650, page 650
1
18
5 8
500 500
500 0.00200
0.002000.000250
82 36.0
2.88 10 2.88 100.000250
cycless
cycles ss cycle
scycle s
cycle
km ms s
Hz
kmv
s
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.2 The Speed of EMR13.2 The Speed of EMR
Check and ReflectCheck and Reflect, page 652, questions , page 652, questions 1 and 31 and 3
SNAPSNAP has a good review of has a good review of electromagnetic spectrum, Maxwell’s electromagnetic spectrum, Maxwell’s theory, and Hertz’s experiment on pages theory, and Hertz’s experiment on pages 142 – 146142 – 146
(worth your time to read) (worth your time to read)
SNAP SNAP Problems, page 224 questions 1, 4, Problems, page 224 questions 1, 4, 6, 9, 126, 9, 12
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Rectilinear PropagationRectilinear Propagation: EMR (e.g. light) : EMR (e.g. light) travels in straight lines through a travels in straight lines through a uniform mediumuniform medium
Smooth surface: get regular reflectionSmooth surface: get regular reflection
Rough surface: diffuse or irregular Rough surface: diffuse or irregular reflection – think about a piece of paper reflection – think about a piece of paper in a bookin a book
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Law of Reflection: angle of reflection = Law of Reflection: angle of reflection = angle of incidence (both measured wrt angle of incidence (both measured wrt normalnormal to the surface) to the surface)
Why is it more sensible to measure wrt Why is it more sensible to measure wrt normalnormal than the surface itself? than the surface itself?
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Virtual imageVirtual image – an image that appears to – an image that appears to be behind a plane mirror (it isn’t really be behind a plane mirror (it isn’t really there)there)
Virtual images are always right side upVirtual images are always right side up
Real imageReal image – an image that can be – an image that can be captured on a screen (it is actually captured on a screen (it is actually there)there)
Real images are always inverted (upside Real images are always inverted (upside down)down)
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Ray diagram for a Ray diagram for a planeplane mirror mirror
Comment about “rays” of lightComment about “rays” of light
• •image
object
Note that image is the same distance behind the mirror as the object is in front of it
normal
normal
Diverging rays: your brain knows light travels in straight lines.
Location of image: where the rays appear to have come from
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Image characteristics:Image characteristics:
magnificationmagnification you know you know
attitudeattitude erect (right side erect (right side up) or invertedup) or inverted
positionposition how far from how far from mirrormirror
typetype real or virtualreal or virtual
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Curved mirrors:Curved mirrors:
ConConcavecave – curved inwards – curved inwards
((convergingconverging – focuses light) – focuses light)
Convex – curved outwardsConvex – curved outwards
((divergingdiverging – spreads light out) – spreads light out)
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Ray diagrams for curved mirrorsRay diagrams for curved mirrors
Use an arrow for the object:Use an arrow for the object:
tail on the principal axistail on the principal axis
draw rays from the tip of the arrow to draw rays from the tip of the arrow to find its position, the tail of the arrow will find its position, the tail of the arrow will be on the principal axisbe on the principal axis
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Draw at least 2, but preferably 3, rays to Draw at least 2, but preferably 3, rays to find the image positionfind the image position
Ray 1Ray 1 – runs parallel to principal axis - – runs parallel to principal axis - reflects through reflects through FF (concave mirror) or (concave mirror) or reflects as if it had come from reflects as if it had come from FF (convex (convex mirror)mirror)
Ray 2Ray 2 – runs through – runs through FF (concave mirror) (concave mirror) or heads towards or heads towards FF (convex mirror) - (convex mirror) - reflects parallel to principal axisreflects parallel to principal axis
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Ray 3Ray 3 – runs through C (concave mirror) – runs through C (concave mirror) or heads towards C (convex mirror) – or heads towards C (convex mirror) – reflects back on itselfreflects back on itself
Find intersection of rays and draw imageFind intersection of rays and draw image
Examples to followExamples to follow
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
••
ray 1
ray 2
ray 3
I
O
F
C
real image, reduced in size
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
•• OF
C
I
ray 1
ray 3; ray 2 is hard to draw
diverging rays – project back
Lets try ray 2 anyway
missed; rays far from principal axis will often not meet perfectly
virtual, enlarged image
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
•• •O I
ray 1
ray 3ray 2
Diverging rays; project back
F C
virtual image, reduced in size
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Summary of curved mirror imagesSummary of curved mirror images
Concave mirrorsConcave mirrors: real, inverted image, if : real, inverted image, if object further than object further than ff from the mirror from the mirror
Virtual, erect, enlarged image if object Virtual, erect, enlarged image if object closer than closer than ff from mirror from mirror
No image if object at No image if object at FF
Convex mirrorsConvex mirrors: virtual, erect, reduced : virtual, erect, reduced image at all distances (right hand car image at all distances (right hand car mirror)mirror)
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Good overview of mirror diagrams – Good overview of mirror diagrams – SNAPSNAP page 174 - 179 page 174 - 179
SNAPSNAP Problems, page 180, 1 a - g Problems, page 180, 1 a - g
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Curved mirror calculations:Curved mirror calculations:
mm = magnification, = magnification, ddoo = object distance, = object distance, ddii = image distance, = image distance, ff = focal length, = focal length, hhii = height of image, = height of image, hhoo = height of = height of objectobject
i i
o o
h dm
h d
1 1 1
i of d d
Sign conventions: (not on formula sheet)
do , ho always (+),
virtual images di (-), real images di (+)
virtual focus f (-), real focus f (+)
hi (+) virtual, (-) real
m (+) virtual, (-) real
On formula sheet
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Example: Example: Practice Problem 1Practice Problem 1, page 664, page 664
ff = -10.0 cm, = -10.0 cm, ddoo = +20.0 cm= +20.0 cm
since since ddii (-), image is virtual (-), image is virtual
-1
1 1 1
1 11
11 1
1 1 1 use the button on your calculator!
10.0 20.0
10.0 20.0 6.67
i o
i o
i
i
xf d d
f d d
cm d cm
d cm cm cm
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Example: Example: Practice Problem 3Practice Problem 3, page 664, page 664
hhoo = 5.0 cm, = 5.0 cm, ddoo = 2.0 cm, = 2.0 cm, mm = -4 (treat as = -4 (treat as -4.0)-4.0)
ddii = ?, = ?, ff = ? = ?
4.02.0
8.0
i
o
i
i
dm
d
dcm
d cm
1 1 1
11 18.0 2.0
1.6
i of d d
f cm cm
cm
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
Check and ReflectCheck and Reflect, page 665, questions , page 665, questions 4, 5, 7, 114, 5, 7, 11
SNAP,SNAP, page 182 questions 2, 3, 5, 6, 7, 9 page 182 questions 2, 3, 5, 6, 7, 9
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
2.2. hhoo=+5.0 cm, =+5.0 cm, ddoo=+7.0 cm, =+7.0 cm, hhii=-5.0 cm, =-5.0 cm, ff=?=?
-5.0
5.0 7.0
7.0
i i i
o o
i
cmh d dh d cm cm
d cm
1 11 1
11
7.0 7.0 0.28
0.28 3.5
f cm cm cm
f cm cm
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
3.3. hhoo=+3.0 cm, =+3.0 cm, ddoo=+6.0 cm, =+6.0 cm, hhii=+1.0 =+1.0 cm, cm, ff=?=?
1.0
3.0 6.0
2.0
i i i
o o
i
cmh d dh d cm cm
d cm
1 11 1
11
2.0 6.0 0.33
0.33 3.0
f cm cm cm
f cm cm
Since f is negative, this a convex mirror – has a virtual focus
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
5.5. ddii=-3.0 cm, =-3.0 cm, ff=-5.0 cm (convex), =-5.0 cm (convex), ddoo=? =?
1 1 1
1 1 1
11 1
5.0 3.0
5.0 3.0 7.5
i o
o
o
f d d
cm cm d
d cm cm cm
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
7.7. ddoo=+5.0 cm, =+5.0 cm, M=M=--2.5 2.5 (real image)(real image), r=, r=??
Important key: radius of curvature Important key: radius of curvature (distance to C) is 2(distance to C) is 2 f f
2.5 12.5
5.0i i
io
d dM d cm
d cm
1 11 1
11
12.5 5.0 0.28
0.28 3.57
2 2 3.57 7.1
f cm cm cm
f cm cm
r f cm cm
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.3 Reflection13.3 Reflection
9.9. hhoo=3.0 cm, =3.0 cm, ddii=-2.5 cm, =-2.5 cm, hhii=+2.0 cm, =+2.0 cm, ff=?=?
2.0 2.5
3.0
3.75
i i
o o o
o
cm cmh dh d cm d
d cm
1 11 1
11
2.5 3.75 0.13
0.13 7.5
f cm cm cm
f cm cm
Since f is negative, this is a convex or diverging mirror
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
RefractionRefraction: a change in direction of light : a change in direction of light due to a change in its speed as it passes due to a change in its speed as it passes from one medium to anotherfrom one medium to another
Notice that angle of refraction is also measured wrt normal
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
refractive indexrefractive index (or index of refraction): (or index of refraction): ratio of speed of light in given medium ratio of speed of light in given medium to speed of light in vacuumto speed of light in vacuum
From low index to high – bends towards From low index to high – bends towards normalnormal
From high index to low – bends away From high index to low – bends away from normalfrom normal
Table of indexes, page 667Table of indexes, page 667
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Snell’s Law:Snell’s Law:
If air is the incident medium, If air is the incident medium,
where where nn is index of refraction of the is index of refraction of the second mediumsecond medium
sin a constant
sini
r
sinsin
air
r
n
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
More complete version when first More complete version when first medium is not airmedium is not air
Doesn’t matter which medium is first or Doesn’t matter which medium is first or second as long as the proper grouping is second as long as the proper grouping is maintainedmaintained
I always use the longer formula even if I I always use the longer formula even if I start in airstart in air
1 2
2 1
sinsin
nn
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Example: Example: Practice Problem 1Practice Problem 1, page 668, page 668
1 2
2 1
sin let medium 1 be diamond, medium 2 be air
sinnn
1 2
2 1
1
1
1
sinsin
sin 1.0003sin25 2.42
sin 0.175
10
nn
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
When refraction occurs, angle at the When refraction occurs, angle at the medium boundary changes, but also:medium boundary changes, but also:
vv changes and changes and λλ changes changes ((ff doesn’t doesn’t change!)change!)
One formula: One formula: 11 1 2
2 2 2 1
sinsin
v nv n
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Example: Example: Practice Problem 1aPractice Problem 1a, page 670, page 670
11 1 2
2 2 2 1
1 2
2 1
18
81
sinsin
let water be medium 1, vacuum be medium 2
1.00003.00 10 1.33
2.26 10
ms
ms
v nv n
v nv n
v
v
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Total internal reflection: Total internal reflection: When light travels from higher index medium to lower one, it refracts away from normal.
If angle of incidence is increased, you eventually reach a point where the angle of refraction = 90°
If angle of incidence is further increased all of light is totally internally reflected
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
critical angle – angle of incidence that critical angle – angle of incidence that causes a refracted angle of 90°causes a refracted angle of 90°
What is critical angle for water/air What is critical angle for water/air interface?interface?
1 2
2 1
1
11
sin let medium 1 be water, medium 2 be air
sin
sin 1.0003sin90 1.33
1.0003sin 48.8
1.33
nn
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Applications of total internal reflection:Applications of total internal reflection:
fibre optic cables for communications fibre optic cables for communications and remote medical imaging, reflecting and remote medical imaging, reflecting mirrors in optical instrumentsmirrors in optical instruments
DemoDemo
Read pages 673 and 674Read pages 673 and 674
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Standard refraction illustration:Standard refraction illustration:
penny in bottom of cup-invisible to viewer
Water is added to cup and penny appears
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Another one:Another one:
Pool looks Pool looks shallower than it shallower than it isis
apparent bottom
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
SNAPSNAP page 165, page 165,
Problems 1, 2, 3, 5, 6, 7, 10, 11, 17*, 18 Problems 1, 2, 3, 5, 6, 7, 10, 11, 17*, 18 hint: equilateral, 20, 22hint: equilateral, 20, 22
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
PrismsPrisms
Dispersion: separation of white light into Dispersion: separation of white light into its constituent colours its constituent colours
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
What causes dispersion?What causes dispersion?
Index of refraction is slightly different for Index of refraction is slightly different for different wavelengths of light.different wavelengths of light.
Violet light (shortest Violet light (shortest λλ) has greatest ) has greatest nn and bends most. Red bends least.and bends most. Red bends least.
Way to remember:Way to remember:
““red refracts rotten; blue bends best”red refracts rotten; blue bends best”
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Lens diagrams very similar to mirror Lens diagrams very similar to mirror diagramsdiagrams
Converging lens – focuses lightConverging lens – focuses light
e.g. double convexe.g. double convex
Diverging lens – spreads light outDiverging lens – spreads light out
e.g. double concavee.g. double concave
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
One difference in the diagrams – a lens One difference in the diagrams – a lens has 2 foci, one on each sidehas 2 foci, one on each side
Draw 3 rays as before – instructions, Draw 3 rays as before – instructions, page 678page 678
Examples to followExamples to follow
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
• •O
I
f
f
Real image, inverted, slightly enlarged
projector lens
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
• •f fO
You are looking at the object through the lens – diverging rays – project back
I
Virtual, erect image, reduced in size
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
• •f fO
Rays diverging – project back
I
virtual, erect, enlarged image
a magnifying glass!
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Generalizations:Generalizations:
Convex lens – real image if object Convex lens – real image if object outside of F, enlarged virtual image outside of F, enlarged virtual image inside F, no image at Finside F, no image at F
Concave lens – always virtual image Concave lens – always virtual image reduced in size reduced in size
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Lens calculations – just like mirror Lens calculations – just like mirror calculations:calculations:
Same formulasSame formulas
Same sign conventionsSame sign conventionsdo , ho always (+),
virtual images di (-), real images di (+)
diverging lens: focus f (-), converging lens: focus f (+)
hi (+) virtual, (-) real
m (+) virtual, (-) real
i i
o o
h dm
h d
1 1 1
i of d d
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.4 Refraction13.4 Refraction
Check and ReflectCheck and Reflect page 683 page 683
Questions 1, 6, 8Questions 1, 6, 8
SNAP Problems, page 194, questions SNAP Problems, page 194, questions
1 a, c, e, g, 2, 5, 6, 7, 11, 141 a, c, e, g, 2, 5, 6, 7, 11, 14
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Huygens’ Principle: Wave front consists Huygens’ Principle: Wave front consists of many small point sources of of many small point sources of “wavelets” that propagate outward in a “wavelets” that propagate outward in a circle at same speed as the wave. circle at same speed as the wave. Wavefront is tangent to wavelets.Wavefront is tangent to wavelets.
wavelets
•
••
•
•••
•••
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Individual wavelets will bend around a Individual wavelets will bend around a small opening as they propagate new small opening as they propagate new circular waves from every point on the circular waves from every point on the waveletwavelet
diffractiondiffraction: when waves meet a small : when waves meet a small opening or the corner of a barrier, they opening or the corner of a barrier, they will bend around the opening will bend around the opening
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Back to Young’s double slit experiment, Back to Young’s double slit experiment, 18011801
anti-nodal line or “bright fringe”
nodal line or “dark fringe”
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Creation of Pattern:Creation of Pattern:
n = 1 antinode – next page
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Constructive interference, producing an antinode will occur whenever the difference in path length is a whole-number, n, of wavelengths
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Destructive interference, producing a Destructive interference, producing a nodal line, will occur whenever nodal line, will occur whenever differencedifference in path length is a half- in path length is a half-number, number, nn/2 of wavelengths/2 of wavelengths
λ
9 λ
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Working with the small triangle at the Working with the small triangle at the bottom of the diagram leadsbottom of the diagram leadsto 2 formulas:to 2 formulas:
and and
sindn
xdnl
λ
9 λ
X
l
θ
when n = 1
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
You may notice that You may notice that
These 2 formulas are not the same. These 2 formulas are not the same. However for small angles (However for small angles (θθ ≤ 10°) sin ≤ 10°) sin and tan are almost exactly the same.and tan are almost exactly the same.
sin tand dl l
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Practice Problem 1Practice Problem 1, page 691, page 691
Practice Problem 3Practice Problem 3, page 691, page 691
2 474.50 10 1.5 10
5.4 102.5 5.0
xd m mm
nl m
17
5
1.00 105.00 10
2.5 1.20
1.50 10
xnl
m
d
dm
md
m
Central antinode to 3rd node (dark fringe)
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
A diffraction grating is a piece of glass A diffraction grating is a piece of glass with a large number of very thin parallel with a large number of very thin parallel scratches on itscratches on it
The scratches block light and spaces The scratches block light and spaces between scratches are slits that light between scratches are slits that light passes throughpasses through
An interference pattern from a An interference pattern from a diffraction grating is the same as a diffraction grating is the same as a double slit pattern except that the light double slit pattern except that the light is brighter since it comes from multiple is brighter since it comes from multiple equally spaced slitsequally spaced slits
diffraction grating – in actual fact lines are so thin and close together you can’t see them
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Example: Example: SNAPSNAP, page 214, question 12, page 214, question 12
SNAPSNAP, page 212, questions 1, 2, 4, 5, 9, , page 212, questions 1, 2, 4, 5, 9, 11, 16 (also good explanation pages 11, 16 (also good explanation pages 200-212)200-212)
14 5 5
57
814
7
6.20 10 1.61 10 1.61 10
0.0522 1.61 105.61 10
1 1.50
3.00 105.34 10
5.61 10
lines mm line
ms
d m
xdnl
m mm
m
cH
mf z
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Poisson’s Bright SpotPoisson’s Bright Spot
Diffraction gratings – as already Diffraction gratings – as already mentioned, brighter patternmentioned, brighter pattern
Also sharper, and spread out wider – Also sharper, and spread out wider – demo with circlesdemo with circles
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
l
screen
central antinode n=1
antinode n=1 antinode
n=2 antinode
n=2 antinode
d
What will happen to x as d is decreased? Discuss
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
l
screen
central antinode n=1
antinode n=1 antinode
n=2 antinode
n=2 antinode
d
anti-nodes get wider and further apart
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Using a diffraction grating to measure Using a diffraction grating to measure the wavelength of visible lightthe wavelength of visible light
Demo with laserDemo with laser
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
At the start of this unit you saw that 2 At the start of this unit you saw that 2 polarizing filters, if oriented one way, will polarizing filters, if oriented one way, will allow light to pass through, but ……..allow light to pass through, but ……..
if one is rotated 90°, they will not allow light to pass throughBecause of this physicists came to believe that light was a transverse wave
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference
Radio waves are already polarized in Radio waves are already polarized in their productiontheir production
SNAPSNAP, page 216 – 218 has a good , page 216 – 218 has a good section on thissection on this
Light and Electromagnetic Radiation – Part 1Light and Electromagnetic Radiation – Part 113.5 Diffraction and Interference13.5 Diffraction and Interference