Maxwell’s Equations - Rutgers ECE
4 1 Maxwell’s Equations The next simplest form of the constitutive relations is for simple homogeneous isotropic dielectric and for magnetic materials: D =E B =μH (1 3 4) These are typically valid at low frequencies The permittivity and permeability μ are related to the electric and magnetic susceptibilities of the material as follows
Lecture: Maxwell’s Equations - USPAS
Maxwell’s Equations A dynamical theory of the electromagnetic field James Clerk Maxwell, F R S Philosophical Transactions of the Royal Society of London, 1865 155, 459-512, published 1 January 1865
Chapter 1 Maxwell’s Equations
To solve Maxwell’s equations (1 15)–(1 18) we need to invoke specific material properties, i e P = f(E) and M = f(B), which are denoted constitutive relations 1 4 Maxwell’s Equations in Differential Form For most of this course it will be more convenient to express Maxwell’s equations in differential form
Chapter 13 Maxwell’s Equations and Electromagnetic Waves
Ampere−Maxwell law 000 dId E dt µµε Φ ∫Bs⋅=+ GG v Electric current and changing electric flux produces a magnetic field Collectively they are known as Maxwell’s equations The above equations may also be written in differential forms as 0 000 0 t t ρ ε µµε ∇⋅ = ∂ ∇× =− ∂ ∇⋅ = ∂ ∇× = + ∂ E B E B E BJ G G
MAXWELL’S EQUATIONS, ELECTROMAGNETIC WAVES, AND STOKES PARAMETERS
MAXWELL EQUATIONS, EM WAVES, & STOKES PARAMETERS 7 nˆ ×(H 2 − H1) = 0 (finite conductivity) (3 10) The boundary conditions (3 1), (3 2), (3 4), (3 9), and (3 10) are useful in solving the differential Maxwell equations in different adjacent regions with continuous physical properties and then linking the partial solutions to
3 Maxwells Equations and Light Waves
In Maxwell’s original notation, the equations were not nearly so compact and easy to understand original form of Maxwell’s equations But, he was able to derive a value for the speed of light in empty space, which was within 5 of the correct answer The modern vector notation was introduced by Oliver Heaviside and Willard Gibbs in 1884
On the Notation of Maxwells Field Equations
equations, for example, contains the vector potential A , which today usually is eliminated Three Maxwell equations can be found quickly in the original set, together with O HM ’s law (1 6) , the F ARADAY-force (1 4) and the continuity equation (1 8) for a region containing char ges The Original Quaternion Form of Maxwell‘s Equations
32-1 Chapter 32
MAXWELL’S CORRECTION TO AMPERE’S LAW As we mentioned in the introduction, Maxwell de-tected a logical flaw in Ampere’s law which, when corrected, gave him the complete set of equations for the electric and magnetic fields With the complete set of equations, Maxwell was able to obtain a theory of light
Maxwell’s Equations & The Electromagnetic Wave Equation
Maxwell’s Equations in vacuum t E B t B E B E o o w w u w w u x x PH 0 0 • The vacuum is a linear, homogeneous, isotropic and dispersion less medium • Since there is no current or electric charge is present in the vacuum, hence Maxwell’s equations reads as • These equations have a simple solution interms of traveling sinusoidal waves,
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Lecture:
at Jefferson Laboratory, January 15-26th2018 FMarhauser
day, January 1 , 2018This Lecture
ˉThis lecture provides theoretical basics useful for follow-up lectures on resonators and waveguidesSources of electromagnetic fields
Some clarifications on all four equations
Time-varying fields AEwave equation
Example: Plane wave
ˉPhase and Group Velocity
ˉWave impedance
2A dynamical theory of the electromagnetic field
James Clerk Maxwell, F. R. S.
Philosophical Transactions of the Royal Society of London, 1865 155, 459-512, published 1 January 1865 -Originally there were 20 equationsSources of Electromagnetic Fields
5ˉElectromagnetic fields arise from 2 sources:
Electrical charge (Q)
Electrical current (ܫ
to quantify the effects of fields: ௌelectric current density -total electric current per unit area S (or ܫൌௌԦܬȉ݀ԦܵStationary charge creates electric field
Moving charge creates magnetic field
ˉIf either the magnetic or electrical fields vary in time, both fields are 6DifferentialForm
D= electric flux density/displacement field (Unit: As/m2)E= electric field intensity (Unit: V/m)
ʌ= electric charge density (As/m3)
H= magnetic field intensity (Unit: A/m)
B= magnetic flux density (Unit: Tesla=Vs/m2)
J= electric current density (A/m2)
Ɋ=permeability of free space
or orGauss's law
Gauss's law for magnetism
Ampğre's law
Faraday's law of induction
(1) (2) (3) (4) form the basic of the classic electromagnetismLorentz ForceDiǀergence (Gauss') Theorem
7 outwardfluxofvectorfield(Ԧܨ {divCurl (Stokes') Theorem
8Green's Theorem
{curlIntegralofcurlofvectorfield(Ԧܨ
lineintegralofvectorfield(ԦܨEdžample͗ Curl (Stokes') Theorem
9Integralofcurlofvectorfield(Ԧܨ
lineintegralofvectorfield(ԦܨExample: Curl (Stokes) Theorem
10 Example: Closed line integrals of various vector fields {curlIntegralofcurlofvectorfield(Ԧܨ
lineintegralofvectorfield(ԦܨNo curlSome curlStronger curl
No net curl
11DifferentialFormIntegralForm
D= electric flux density/displacement field (Unit: As/m2)E= electric field intensity (Unit: V/m)
H= magnetic field intensity (Unit: A/m)
B= magnetic flux density (Unit: Tesla=Vs/m2)
J= electric current density (A/m2)
Gauss' theorem
Stokes' theorem
Ɋ=permeability of free space
Gauss's law
Gauss's law for magnetism
Ampğre's law
Faraday's law of induction
ʌ= electric charge density (C/m3=As/m3)
121. Uniform field
Electric Flux & 1stMaxwell Equation
-angle between field and normal vector to surface mattersGauss: Integration over closedsurface
2. Non-Uniform field
Example: Metallic plate,
assume only surface charges on one sideDefinition of Electric Flux
13Gauss: Integration over closedsurface
Example: Capacitor
Electric Flux & 1stMaxwell Equation
1. Uniform field
-angle between field and normal vector to surface matters2. Non-Uniform field
Definition of Electric Flux
14Integration of over closed spherical surface S
Examples of non-uniform fields
Point charge Q
Principle of Superposition holds:
Electric Flux & 1stMaxwell Equation
pointing out radiallyAdd charges
15Uniform field
Magnetic Flux & 2ndMaxwell Equation
Gauss: Integration over closedsurface
Non-Uniform field
Definition of Magnetic Flux
-There are no magnetic monopoles -All magnetic field lines form loopsClosed surface:
Flux lines out = flux lines in
What about this case?
Flux lines out > flux lines in ?
-No. In violation of 2ndMadžwell's law, i.e. integration over closed surface, no holes allowed -Also: One cannot split magnets into separate poles, i.e. there always will be aNorth and South pole
16Magnetic Flux & 3rdMaxwell Equation
Faraday's law of induction
If integration path is not changing in time
-Change of magnetic flux induces an electric field along a closed loop -Note: Integral of electrical field over closed loop may be non-zero, when induced by a time-varying magnetic field -Electromotive force (EMF) ם charge traveling once around loop 17 -Change of magnetic flux induces an electric field along a closed loopMagnetic Flux & 3rdMaxwell Equation
-Electromotive force (EMF) ם -Note: Integral of electrical field over closed loop may be non-zero, when induced by a time-varying magnetic fieldIf integration path is not changing in time
charge traveling once around loop -or voltage measured at end of open loopFaraday's law of induction
18 Ampère's (circuital) Law or 4thMaxwell Equation -Note that ௌԦܬȉ݀Ԧܵ haǀe arbitrary shape as long as эS is its closed boundary -What if there is a capacitor? -While current is still be flowing (charging capacitor): tangential to a circle at any radius r of integration {conduction current IRight hand side of equation:
Left hand side of equation:
19 Ampère's (circuital) Law or 4thMaxwell Equation {displacement current I -But one may also place integration surface Sbetween plates AEcurrent does not flow through surface here -This is when the displacement field is required as a corrective 2ndsource term for the magnetic fields tangential to a circle at any radius r of integration ; Gauss's law {conduction current ILeft hand side of equation:
20 conduction current displacement current -In resistive materials the current density Jis proportional to the electric field =1/the electric resistivity (ё·m) -Generally (ʘ, T) is a function of frequency and temperaturePresence of Resistive Material
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