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


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


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)


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


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


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


Double-slit experiment: Double-slit experiment: observed!


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


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:


•• 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


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


Hertz – verification of existence of Hertz – verification of existence of electromagnetic waveselectromagnetic waves


Demos of a Hertz-like experimentDemos of a Hertz-like experiment

AM and FM radio wavesAM and FM radio waves


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


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


Michelson’s method – 1905 (awarded Michelson’s method – 1905 (awarded Nobel prize for this)Nobel prize for this)

Example: Practice Problem 3, page 650


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


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


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?


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)


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


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


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)


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


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


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


••

ray 1

ray 2

ray 3

I

O

F

C

real image, reduced in size


•• 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


•• •O I

ray 1

ray 3ray 2

Diverging rays; project back

F C

virtual image, reduced in size


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)


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


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


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



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


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


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


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


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


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


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


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


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


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



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


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


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


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


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


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


Standard refraction illustration:Standard refraction illustration:

penny in bottom of cup-invisible to viewer

Water is added to cup and penny appears


Another one:Another one:

Pool looks Pool looks shallower than it shallower than it isis

apparent bottom


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


PrismsPrisms

Dispersion: separation of white light into Dispersion: separation of white light into its constituent colours its constituent colours


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”


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


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


• •O

I

f

f

Real image, inverted, slightly enlarged

projector lens


• •f fO

You are looking at the object through the lens – diverging rays – project back

I

Virtual, erect image, reduced in size


• •f fO

Rays diverging – project back

I

virtual, erect, enlarged image

a magnifying glass!


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


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


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

•

••

•

•••

•••


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


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”


Creation of Pattern:Creation of Pattern:

n = 1 antinode – next page


Constructive interference, producing an antinode will occur whenever the difference in path length is a whole-number, n, of wavelengths


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


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


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




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)


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


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


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


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


l

screen

central antinode n=1

antinode n=1 antinode

n=2 antinode

n=2 antinode

d

anti-nodes get wider and further apart


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


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


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 1 to accompany pearson physics powerpoint presentation...

Documents

visible light

s light

light travel

electromagnetic spectrumlight

electromagnetic spectrumtable

infrared light

ultraviolet light

msspeed of light