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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