Download Spring 2014 - PHYS4202/6202 - E&M II (Dr. Andrei Galiautdinov, UGA) 0

Spring 2014 - PHYS4202/6202 - E&M II
(Dr. Andrei Galiautdinov, UGA)
Lectures 1 - 28
Magnetic dipole
Magnetic quadrupole
0
Lecture 1 (Tuesday, Jan. 07/2014)
• ED: Classical electrodynamics overview
• ED: Operational definition of electric & magnetic fields
• ED: Maxwell’s equations in local & integral form (and brief discussion
of where they come from)
• ED: Time-independent situation (electrostatics, magnetostatics)
1
2
The Field Concept
(took 2,500 years to arrive at)
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
5
The Field Concept (1)
1)
Taken literally, Coulomb’s Law describes an Action-at-a-Distance Model of
electrostatic interactions in which charges (charged particles) exert forces directly
and instantaneously on one another across the distance separating them.
Note: these forces act along the lines connecting the charges
Symbolically: charge  charge
2) This model is good when charges are at rest.
3) Problems arise when charges are allowed to move.
Example:
•
Charge 1 on Earth, charge 2 on Moon.
•
If charge 1 wiggles (for whatever reason), charge 2 (according to Coulomb) would immediately
experience a different force.
•
This doesn’t seem right!
•
This leads to violation of STR, according to which no influence can propagate faster than the speed
6
of light.
The Field Concept (2)
1)
The Field Model instead imagines that a charge particle creates a field in the space
around it, and another particle responds to the field at its own location, not to the first
particle directly.
Symbolically: charge  field  charge
2) How does this resolve the problem of moving charges?
In our previous example:
•
When charge 1 is wiggled, it does not directly affect the distant charge 2.
•
Rather, the wiggling particle wiggles the values of the field in its immediate vicinity.
•
These wiggles in turn affect the field values at slightly more distant locations, and so on.
•
The net effect is that ripples in the field move away from the wiggling particle at a finite speed
(similar to how ripples on the surface of water do; the difference is, the ripples in the field do not
need any medium to propagate in, so they can propagate in a vacuum).
•
As a result, only when the ripples reach the distant charged particle will it feel a wiggling force.
The Field Concept (3)
1)
A field, (unlike a particle) exists not at a specific location but throughout
space.
2) Even so, the field is a physical object (entity) that (like a particle) has energy,
carries momentum, and obeys its own equations of motion.
3) We need a field model b/c instantaneous action at a distance violates STR
(no signal can propagate faster than the speed of light). The Field Model
naturally resolves this problem.
4) Mathematically, we describe a field (formally) by assigning some kind of
numerical quantity to every point in space at every moment in time – in our
case, vectors.
5) Physically, we define the field (operationally) in terms of what it does – in our
case, in terms of forces it exerts on charged particles.
The Field Concept (4)
1)
So, physically, we define the field (operationally) in terms of what it does –
in our case, in terms of forces it exerts on charged particles.
2)
Here’s how it works:
- +
+ -- -+
+-+-+
+
+-
P
Bring in qtest and hold it at
rest; then measure the force
on it.
3) Then, by definition:
Distribution of charge
(regarded as the source of
the field at point P). Charges
in this distribution are allowed
to move arbitrarily.


Fe
E
qtest
By definition:
The Field Concept (5)


Fe
E
qtest
Translation:
a)
This eq. defines the E-field vector at a point in space & time.
b) Fe is the electrostatic force experienced at that time by a small test particle with charge qtest held
at rest at that point in space.
c)
qtest must be small, so that the force it exerts on the charges in the distribution does not push
around the charges whose field we are trying to measure.
d) E-vector points in the same direction as Fe if qtest is positive.
e)
Why divide Fe by qtest? – B/c it is found experimentally that, no matter how source charges move,
the force Fe the test charge experiences at a given location is proportional to qtest itself. So,
dividing by qtest produces a quantity E that depends only on position relative to the charges
creating the field and not on the magnitude of the test charge qtest we use.
f)
Why keep qtest at rest? – B/c if qtest moves (has non-zero velocity) it will experience an additional
force (magnetic force) due to motion of the source charges.
By definition:
Note:
The Field Concept (6)


Fe
E
qtest
E-field is a vector quantity, but it is important to remember that it consists of an infinite number
of vectors attached to every point in space at any moment in time.
To describe the E-field fully you must specify E-vectors everywhere.
Unit: [E] = N/C
Examples:
1. On a sunny day, due to various atmospheric processes that separate charges,
E = 100 to 150 (N/C)
2. During a thunderstorm, E > 10,000 (N/C)
3. When taking a shower, by moving water, E ~ 800 (N/C)
4. In dry air, if E > 3,000,000 (N/C), the air breaks and becomes a conductor, sparks fly.
The Field Concept (7)
Once the E-field has been determined, we can find the force it exerts on
any charged particle by:


Fe  qE (any charge; limitations apply)
Note:
Fe
E
(if q > 0)
Fe
E
(if q < 0)
Lecture 2 (Thursday, Jan. 09/2014)
•
•
•
•
ED: The meaning of current density j
ED: (Local) charge conservation & continuity equation
MS: Steady currents confined to finite volume
MS: Magnetic vector potential A
13
14
15
16
17
18
Lecture 3 (Tuesday, Jan. 14/2014)
• VC: The meaning of the Laplacian
• MS: Formula for magnetic vector potential A
19
20
21
Roughly speaking:
The Laplacian provides a measure of the difference b/w the
average value of the field in the immediate neighborhood of
the point and the precise value of the field at the point.
It is a three-dimensional generalization of the second
derivative; characterizes “average” three-dimensional
concavity of the function.
22
23
Lecture 4 (Thursday, Jan. 16/2014)
• MS: Restriction on j
• MS: Magnetic dipole moment (preliminary discussion)
• MS: Magnetic dipole moment of a planar loop with current (preliminary
discussion)
• MS: Multipole expansion of the vector potential (up do dipole - intro)
24
The formula for A is applicable to current distributions j that go to zero
sufficiently quickly as r increases (otherwise, the volume integral would not
converge).
25
typo
Here we are dealing with j that is localized (confined to a finite volume). Our
goal is to find A at large r.
26
27
28
29
Lecture 5 (Tuesday, Jan. 21/2014)
• MS: Multipole expansion of the vector potential (up do dipole – cont.)
30
31
32
33
34
Lecture 6 (Thursday, Jan. 23/2014)
• VC: “Rotor of a vector product” formula
• MS: Magnetic field of a magnetic dipole
• MS: Magnetic field of a straight current (quick derivation from
Maxwell’s 4th equation)
• MM: Ampere’s hypothesis
35
36
This is the formula for the B-field of a magnetic dipole.
Knowledge of this formula is a must. Do not forget the
factor of 3 in front of the first term!
…finish this derivation on your own…
Notice that the current distribution j can be anything, as
long as it’s localized. I used a loop with current for
illustration only.
37
Here we are looking at the B-field at various remote
locations in the “equatorial plane” orthogonal to the
magnetic dipole moment vector m. Again, notice that the
current distribution j can be anything, as long as it’s
localized. I used a loop with current for illustration only.
38
A striking similarity between the B-fields of a coil with current and
a small bar magnet led Ampere to his “molecular currents”
hypothesis.
Here we recalled how
to find the B-field of a
straight current directly
from Maxwell’s 4th
equation.
39
Lecture 7 (Tuesday, Jan. 28/2014)
• MS: Magnetic dipole moment of a plain loop with current
• MS: Magnetic dipole moment of an orbiting electron in the H-atom
• MS: Some simple estimates
40
41
42
43
44
Lecture 8 (Thursday, Jan. 30/2014)
• MECH: Review of work, energy, Work-kinetic-Energy Theorem
(WkET), the Law of Conservation of mechanical Energy (LCE)
• MS: Behavior of a magnetic dipole in the magnetic field: torque,
energy, force
• MS: Conceptual introduction to magnetism in matter
• MS: Demo: Diamagnetic response
• MS: Magnetization, M(r)
• MS: The starting formula for calculation of magnetic vector potential
A(r) of a magnetized object
45
46
47
48
49
50
Lecture 9 (Tuesday, Feb. 04/2014)
• MS: Magnetic field of an infinitely long solenoid with current.
• MS: Magnetic vector potential A(r) of a magnetized object
51
52
53
54
Lecture 10 (Thursday, Feb. 06/2014)
• MS: Magnetic vector potential A(r) of a magnetized object (cont.)
• VC: Divergence Theorem; Modified Divergence Theorem
• VC: Cylindrical coordinate system
• MS: Prob. 6.7. Infinitely long uniformly magnetized cylinder
• MS: Prob. 6.8. Infinitely long non-uniformly circularly magnetized
cylinder (intro)
• MS: A remark on old-fashioned magnetic core memory
55
56
57
58
59
60
Magnetic core memory
61
Magnetic core memory
Magnetic-core memory was the
predominant form of random-access
computer memory from 1955 to 1975.
It uses tiny magnetic toroids (rings), the
cores, through which wires are threaded
to write and read information.
Each core represents one bit of
information. The cores can be
magnetized in two different ways
(clockwise or counterclockwise) and the
bit stored in a core is 0 or 1 depending
on that core's magnetization direction.
Magnetization is changed by sending
appropriate electric current pulses
through selected wires.
A 32 x 32 core memory plane
storing 1024 bits of data.
The process of reading the core causes
the core to be reset to a "zero", thus
erasing it. This is called destructive
readout.
62
Magnetic core memory
Close-up of a core plane. The green horizontal wires are Y; the X wires are dull brown
and vertical, toward the back. The sense wires are diagonal, colored orange, and the
inhibit wires are vertical twisted pairs.
63
Magnetic core memory
“WRITE” OPERATION:
Wires that pass through the cores create magnetic
fields.
Only B > Bcritical ("select") can cause the core to
change its magnetization.
To select a memory location, one of the X and one of
the Y lines are driven with half the current ("halfselect") required to cause this change. Only the
combined B-field generated where the X and Y lines
cross is sufficient to change the state; other cores will
see only half the needed field ("half-selected"), or
none at all.
Driving the current through the wires magnetizes the
core in one direction (“1”) or the other (“0”).
Diagram of the “rectangular” hysteresis curve
for a magnetic memory core during a read
operation. Sense line current pulse is high
("1") or low ("0") depending on original
magnetization state of the core.
The toroidal shape of a core is preferred: since the Mlines are closed, there are no magnetic poles and thus
very little external flux. This allows the cores to be
packed closely together without allowing their
magnetic fields to interact. The alternating 45-degree
positioning in a core array helps to reduce any stray
64
coupling.
Magnetic core memory
“READ” OPERATION:
To read a bit, the circuitry tries to flip the bit’s
magnetization to that assigned to the 0 state, by
driving the selected X and Y lines that intersect at that
core.
If the bit was already 0, the physical state of the core is
unaffected.
If the bit was previously 1, then the core changes
magnetic polarity. This change, after a delay, induces a
voltage pulse into the Sense line (Faraday’s
induction!).
The detection of such a pulse means that the bit had
most recently contained a 1.
Absence of the pulse means that the bit had contained
a 0.
Diagram of the “rectangular” hysteresis curve
for a magnetic memory core during a read
operation. Sense line current pulse is high
("1") or low ("0") depending on original
magnetization state of the core.
The delay in sensing the voltage pulse is called the
access time of the core memory.
Following a read, the bit contains a 0. The information
65
must immediately be rewritten.
Magnetic core memory
8 bytes vs 8 GB:
This microSDHC (Secure Digital High Capacity) card holds about 8½ billion bytes (8
GB). It rests on a section of magnetic-core memory that uses 64 cores to hold eight
bytes. The microSDHC card holds over one billion times more bytes in much less
physical space.
66
Lecture 11 (Tuesday, Feb. 18/2014)
• MS: Prob. 6.8. Infinitely long non-uniformly circularly magnetized
cylinder (cont.)
• Maxwell’s equations in the presence of magnetics
• Paramagnetics, diamagnetics, magnetic susceptibility
67
68
69
70
71
Lecture 12 (Thursday, Feb. 20/2014)
• Maxwell’s equations in the presence of magnetics (cont.)
• Paramagnetics, diamagnetics, magnetic susceptibility
• Example 1: Long solenoid filled with a magnetic
• Example 2: Long straight current immersed in a magnetic
72
73
74
75
76
77
78
Lecture 13 (Tuesday, Feb. 25/2014)
• Review of Maxwell’s Equations in a vacuum (again)
• Faraday’s Law of Induction as a first step towards electrodynamics
• Lenz Rule
• Demos
79
80
81
Michael Faraday, 1842
82
Michael Faraday, 1861
Joseph Henry, ~1865
83
Primary coil (with battery)
Secondary coil (with galvanometer)
84
Primary coil (with battery)
Recreating Faraday’s experiment
Secondary coil (with galvanometer)
85
Another way to change flux: spin the magnet
86
Another way to change flux: spin the magnet
87
88
89
90
Lecture 14 (Thursday, Feb. 27/2014)
• Faraday’s Law of Induction (cont.)
• Units of various physical quantities
• Demo: Eddy currents; a falling magnet
• Some formal math stuff
• Example: Induced electric field inside of a solenoid with changing
current (uniform time-dependent B-field)
• Examples: Conceptual stuff related to Lentz Rule
91
92
A loop with current is like a magnet:
Aside: Actually, it was Ampere’s brilliant realization (circa 1821) that magnetic properties of
magnets are entirely due to the tiny, microscopic, “molecular” currents circulating inside the
magnetic material. Modern physics supports this view: the molecular currents are due to the
orderly spinning motion of the electrons. As a result, we now believe that ALL magnetic fields
93
come from currents, either macroscopic, microscopic, or both.
Demo 1: a magnet falling in a
hollow conducting tube
94
95
96
97
98
Lecture 15 (Tuesday, Mar. 04/2014)
• Recall the static case: time independence,
𝜕𝜌
𝜕
𝜕𝑡
= 0, and local charge
conservation, + 𝛻 · 𝒋 = 0, result in a restriction on j, 𝛻 · 𝒋 = 0. This
𝜕𝑡
restriction is consistent with the “static” Maxwell’s equations.
• Allowing time dependence by adding Faraday’s Law, doesn’t remove
the constraint 𝛻 · 𝒋 = 0; this forbids any charge accumulation.
• Paradox: There are processes, in which charge accumulation are
clearly possible! For example, discharging sphere,
charging/discharging a capacitor.
• Demo 1: Camera flash based on a capacitor.
• Demo 2: Alternating current flows through the capacitor.
• Maxwell’s resolution of this paradox (1864): Displacement current.
• Complete system of Maxwell’s Equations (in a vacuum).
99
100
101
102
Demo 1: Camera flash based on a capacitor
conductor
conductor
insulator
C = 6,000 [μF]
insulating pad
Initially: switch open, capacitor is not charged
Switch thrown left: capacitor is quickly charged
Switch thrown right: capacitor drives a brief current through the light bulb and ammeter.
103
104
Possible design:
I added this ammeter just
to be able to “see”
(measure) the current
through the light bulb.
105
Initially: switch open,
capacitor is not charged.
106
Switch thrown left: capacitor is
quickly charged.
No current in this part
of the circuit
Light bulb is OFF
107
Switch thrown right:
capacitor drives a brief
current through the light
bulb and ammeter.
Now we have a brief
current in this part of
the circuit
Light bulb is ON
108
Demo 2: Alternating current flows through a capacitor
109
Lecture 16 (Thursday, Mar. 06/2014)
• Complete system of Maxwell’s Equations (in a vacuum)
• Local charge conservation as a consequence of ME
• Consistency of the Maxwell’s equations; differential consequences*
• Law of Conservation of Energy in the presence of the electromagnetic
field
• Poynting’s Vector
• Examples: Electromagnetic energy flow in various situations
110
111
112
113
114
115
116
Lecture 17 (Tuesday, Mar. 18/2014)
Time-dependent electromagnetic fields
PLAN:
•
Electromagnetic potentials
•
Gauge invariance
•
Differential equations for electromagnetic potentials; the Lorentz gauge
•
EMF of a uniformly moving charge – Directly from the wave equation
•
Retarded potentials
•
A note on the use of advanced potentials when boundary conditions at a finite
distance from source have to be maintained.
•
Plane EM waves generated by a uniform time-dependent planar current
•
Intuitive understanding of radiation by an accelerated charge
•
EMF of a linearly accelerated charge (graphical derivation in the non-relativistic
limit in the radiation zone)
•
EMF of a time-dependent point dipole
117
Lecture 18 (Thursday, Mar. 20/2014)
Time-dependent electromagnetic fields
•
EMF of a uniformly moving charge – Directly from the wave equation
118
119
120
121
122
123
Lecture 19 (Tuesday, Mar. 25/2014)
Time-dependent electromagnetic fields
•
EMF of a uniformly moving charge – Directly from the wave equation (cont.)
124
125
126
127
128
129
130
131
Lecture 20 (Thursday, Mar. 27/2014)
Time-dependent electromagnetic fields
•
EMF of a uniformly moving charge – Directly from the wave equation (cont.)
132
133
134
135
136
Lecture 21 (Tuesday, Apr. 01/2014)
Time-dependent electromagnetic fields
•
Retarded potentials
•
A note on the use of advanced potentials when boundary conditions at a finite
distance from source have to be maintained.
•
Plane EM waves generated by a uniform time-dependent planar current
137
138
139
140
141
Lecture 22 (Thursday, Apr. 03/2014)
Time-dependent electromagnetic fields
•
Plane EM waves generated by a uniform time-dependent planar current (cont.)
•
Intuitive understanding of radiation by an accelerated charge
•
EMF of a linearly accelerated charge (graphical derivation in the non-relativistic
limit in the radiation zone)
142
143
144
145
146
Lecture 23 (Tuesday, Apr. 08/2014)
Time-dependent electromagnetic fields
•
EMF of a time-dependent point dipole (Model)
147
148
149
Lecture 24 (Thursday, Apr. 10/2014)
Time-dependent electromagnetic fields
•
EMF of a time-dependent point dipole (Model – cont.)
•
EMF of a time-dependent point dipole (Potentials)
150
151
152
153
154
155
156
Lecture 25 (Tuesday, Apr. 15/2014)
Time-dependent electromagnetic fields
•
EMF of a time-dependent point dipole (E - field)
157
158
159
Lecture 26 (Thursday, Apr. 17/2014)
Time-dependent electromagnetic fields
•
EMF of a time-dependent point dipole (B - field)
•
EMF of a time-dependent point dipole (Poynting’s vector)
•
The blueness of the sky
160
161
162
163
164
Lecture 27 (Tuesday, Apr. 22/2014)
A bit of Special Relativity
•
Special Relativity as a Theory of Space and Time
•
Inertial reference frames, properties of space & time, relativity principle
•
Derivation of Lorentz transformation (without Einstein’s 2nd Postulate)
165
166
167
Lecture 28 (Thursday, Apr. 24/2014)
A bit of Special Relativity
•
Derivation of Lorentz transformation (without Einstein’s 2nd Postulate – cont.)
•
Limiting speed
•
Velocity addition formula
•
Invariance of the limiting speed
•
Speed of light
168
169
170
171
172
173
End of Lectures
174
A bit of history…
This is an original map created in 1565 which shows the known world of the day. This old map
gives an incredible view of the New World, recently discovered by Christopher Columbus. The map
has a lot of interesting artwork, including pictures of period ships sailing the ocean. The map is
175
titled, "Vniversale descrittione di tvtta la terra conoscivta fin qvi."
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Thales of Miletus (6th century BC)
is credited with observing that
rubbing fur on various
substances, such as amber, would
cause an attraction between the
two, which is now known to be
caused by static electricity.
The Ancient Greeks noted that the
amber buttons could attract light
objects such as hair and that if the
amber was rubbed sufficiently a
spark would jump.
177
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
William Gilbert (24 May 1544 – 30
November 1603), also known as
Gilberd was an English physician,
physicist and natural philosopher.
He is remembered today largely for
his book De Magnete (On the Magnet
and Magnetic Bodies, and on the
Great Magnet the Earth), published in
1600, and is credited as one of the
originators of the term "electricity".
He is regarded by some as the father
of electrical engineering or electricity
and magnetism.
The English word "electricity" was
first used in 1646 by Sir Thomas
Browne, derived from Gilbert's 1600
New Latin electricus, meaning "like
amber". The term had been in use
since the 13th century, but Gilbert
was the first to use it to mean "like
amber in its attractive properties".
179
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Charles François de Cisternay
DuFay (14 September 1698 – 16
July 1739) in Volume 38 of the
Philosophical Transactions of the
Royal Society (1734), describing
his discovery of the distinction
between two kinds of electricity:
"resinous," produced by rubbing
bodies such as amber, copal, or
gum-lac with silk or paper, and
"vitreous," by rubbing bodies as
glass, rock crystal, or precious
stones with hair or wool.
He also posited the principle of
mutual attraction for unlike forms
and the repelling of like forms and
that "from this principle one may
with ease deduce the explanation
of a great number of other
phenomena."
The terms resinous and vitreous
were later replaced with the terms
"positive" and "negative" by
William Watson and Benjamin
181
Franklin.
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Benjamin Franklin (January 17, 1706 –
April 17, 1790) establishes the link
between lightning and electricity by the
flying a kite into a thunderstorm and
transferring some of the charge into a
Leyden jar.
He is credited with utilizing the concepts
of positive and negative charge. The
charge of any object would be neutral if
the concentration of these charges were
the same.
In 1749 he had documented the similar
properties of lightning and electricity,
such as that both an electric spark and a
lightning flash produced light and sound,
could kill animals, cause fires, melt metal,
destroy or reverse the polarity of
magnetism, and flowed through
conductors and could he concentrated at
sharp points.
183
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Charles-Augustin de Coulomb (14 June
1736 – 23 August 1806) was a French
physicist.
He is best known for developing
Coulomb's law (the inverse-square law
of electrostatics).
The SI unit of electric charge, the
coulomb, was named after him.
185
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Hans Christian Ørsted (14 August 1777 –
9 March 1851) was a Danish physicist
and chemist who united the separate
sciences of electricity and magnetism.
He discovered that electric currents
create magnetic fields, an important
aspect of electromagnetism, confirming
a direct relationship between electricity
and magnetism.
The oersted unit of magnetic induction
(in the CGS system) is named after him.
187
André-Marie Ampère (20 January 1775 – 10
June 1836), professor of mathematics at the
Ecole Polytechnique, a short time after learning
of Ørsted's discovery that magnetic needle is
acted on by a voltaic current, conducts
experiments and publishes a paper in Annales
de Chimie et de Physique (1820) attempting to
give a combined theory of electricity and
magnetism.
He shows that a coil of wire carrying a current
behaves like an ordinary magnet and suggests
that electromagnetism might be used in
telegraphy. He mathematically develops
Ampère's law describing the magnetic force
between two electric currents. His theory
predicts that parallel conductors currying
current in the same direction attract and those
carrying currents in the opposite directions
repel one another.
One of the first to develop electrical measuring
techniques, he built an instrument utilizing a
free-moving needle to measure the flow of
electricity, contributing to the development of
the galvanometer.
The SI unit of measurement of electric current,
188
the ampere, is named after him.
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Michael Faraday (22 September 1791 – 25
August 1867), one of the most influential
scientists in history.
Discoveries include:
•
•
•
•
•
•
Michael Faraday, 1842
The concept of the electromagnetic field
Faraday's law of electromagnetic induction
Electrochemistry (Faraday's laws of
electrolysis; Faraday constant)
Chemistry (discovered benzene, invented
an early form of the Bunsen burner and the
system of oxidation numbers, and
popularized terminology such as anode,
cathode, electrode, and ion.)
Faraday effect (magnetic field causes a
rotation of the plane of polarization of light
- the first experimental evidence that light
and electromagnetism are related)
Faraday wheel (which formed the
foundation of electric motor technology.)
The SI unit of capacitance, the farad, is named
in his honor.
+1 +6 -2
H2SO4
Albert Einstein kept a picture of Faraday on
his study wall, alongside pictures of Isaac
190
Newton and James Clerk Maxwell.
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
James Clerk Maxwell (13 June 1831 – 5
November 1879).
In 1865 publishes his landmark paper “A
Dynamical Theory of the Electromagnetic Field”,
in which his Maxwell's equations demonstrated
that electric and magnetic forces are two
complementary aspects of electromagnetism.
He shows that the associated complementary
electric and magnetic fields of electromagnetism
travel through space, in the form of waves, at a
constant velocity of 3.0 × 108 m/s.
He also proposes that light is a form of
electromagnetic radiation and that waves of
oscillating electric and magnetic fields travel
through empty space at a speed that could be
predicted from simple electrical experiments.
Using available data, he obtains a velocity of
310,740,000 m/s and states "This velocity is so
nearly that of light, that it seems we have strong
reason to conclude that light itself (including
radiant heat, and other radiations if any) is an
electromagnetic disturbance in the form of waves
propagated through the electromagnetic field
according to electromagnetic laws."
192
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Heinrich Hertz (22 February 1857 – 1
January 1894).
In 1888 demonstrates the existence of
electromagnetic waves by building an
apparatus that produced and detected
UHF radio waves (or microwaves in
the UHF region).
He also found that radio waves could
be transmitted through different types
of materials and were reflected by
others, the key to radar.
His experiments explain reflection,
refraction, polarization, interference,
and velocity of electromagnetic
waves.
The unit of frequency – cycles per
second – was named the hertz in his
honor.
194
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
A bit of history…
ancient Greeks:
William Gilbert:
1.
2.
Electrification is not limited
to amber; it’s a general
phenomenon
Amber (by wool) + feather
Magnetite (Fe2O3) + iron
- 700
0
Charles Dufay (King of
France’s gardener):
1733
1600
Hans Oersted:
Michael Faraday:
Inverse-square force
law for electricity
Connection b/w electricity
and magnetism (compass
needle is deflected by
current)
1.
2.
Heinrich Hertz:
Produced EM waves
in the lab
1887
Concept of E & M fields
EM Induction (changing
magnetic field produces
current in a circuit)
1831
1820
Alexander Popov
Joseph Thomson:
Guglielmo Marconi:
Discovery of the
Radio
electron
1896
1. + and – electricity
2. Likes repel,
opposites attract
Electrically charged objects
can also repel each other
Charles Coulomb:
1785
Benjamin Franklin:
1897
1750
James Clerk Maxwell:
1. Laws of E&M in
modern form
2. Existence of EM
waves
3. Light is an EM
wave
1865 to 1873
P. N. Lebedev:
E. Rutherford:
Niels Bohr:
Light pressure
“planetary”
model of atom
“(semi-)
quantum” model
of atom
1900
1911
1913
Pyotr Nikolaevich Lebedev (24
February 1866 - 1 March 1912).
Was the first to measure the
pressure of light on a solid body
in 1899.
The lunar crater Lebedev is
named after him.
197
198
The End
199