-\((r, \theta, \phi)\). \(\theta\) is the polar angle, \(\phi\) the azimuthal angle.
+In this system, we use coordinates \((r, \theta, \varphi)\) in
+which \(r\) is the distance from the chosen origin,
+\(\theta\) is the polar angle and \(\varphi\) is the azimuthal angle.
+
+The usual Cartesian coordinates relate to spherical coordinates
+according to
+
+
+
+
+
+
+
+
+
+
+
\[
-x = r \sin \theta \cos \phi,
-y = r \sin \theta \sin \phi,
+x = r \sin \theta \cos \varphi, \hspace{5mm}
+y = r \sin \theta \sin \varphi, \hspace{5mm}
z = r \cos \theta.
-\label{Gr(1.62)}
+\tag{sph_xyz}\label{sph_xyz}
\]
-Careful: these unit vectors are direction dependent, i.e. we should really
-write \(\hat{\boldsymbol r} (\theta, \phi), \hat{\boldsymbol \theta} (\theta, \phi), \hat{\boldsymbol \phi} (\theta, \phi)\).
+Do be careful: these unit vectors are direction dependent, i.e. we should really
+write \(\hat{\boldsymbol r} (\theta, \varphi)\),
+\(\hat{\boldsymbol \theta} (\theta, \varphi)\)
+and \(\hat{\boldsymbol \varphi} (\theta, \varphi)\).
-Infinitesimal displacement \(d{\bf l}\):
+An infinitesimal displacement \(d{\bf l}\) can be written as
+
+
+
+
+
+
+
+
+
\[
-d{\bf l} = dr \hat{\boldsymbol r} + r d\theta \hat{\boldsymbol \theta} + r\sin \theta d\phi \hat{\boldsymbol \phi}.
-\label{Gr(1.68)}
+d{\bf l} = dr ~\hat{\boldsymbol r} + r d\theta ~\hat{\boldsymbol \theta} + r\sin \theta d\varphi ~\hat{\boldsymbol \varphi}.
+\tag{sph_dl}\label{sph_dl}
\]
\({\boldsymbol \nabla} \cdot ({\boldsymbol \nabla} T) \equiv {\boldsymbol \nabla}^2 T\) is called the Laplacian of the scalar field \(T\).
The Laplacian of a vector field \({\boldsymbol \nabla}^2 {\bf v}\) is also defined as the vector with components
@@ -1610,36 +1610,36 @@ given by the Laplacian of the corresponding vector elements.
diff --git a/build/emd_Fl_Fl.html b/build/emd_Fl_Fl.html
index 4b295c1..8b94a11 100644
--- a/build/emd_Fl_Fl.html
+++ b/build/emd_Fl_Fl.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1638,7 +1638,7 @@ Empirically: the changing magnetic field induces an electric current around
the circuit. This current is really driven by an electric field having a component
along the wire. The line integral of this field is called the
-
+
Electromotive force (or electromotance),
\[
@@ -1660,7 +1660,7 @@ to the rate of change of the magnetic flux,
\]
so we obtain
-
+
Faraday's law (integral form N.B.: for a stationary loop)
\[
@@ -1678,7 +1678,7 @@ for any loop (on a wire or not). Using Stokes' theorem,
\]
we obtain
-
+
Faraday's law (differential form)
\[
@@ -1715,7 +1715,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_Fl_e.html b/build/emd_Fl_e.html
index a4cd06a..de21585 100644
--- a/build/emd_Fl_e.html
+++ b/build/emd_Fl_e.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1657,7 +1657,7 @@ W = \frac{1}{2\mu_0} \left[ \int_{\cal V} d\tau B^2 - \int_{\cal V} d\tau {\bold
\]
We can integrate over all space: after neglecting boundary terms (assuming fields fall to zero at infinity), we are left with
-
\paragraph{Example 7.10:}
short solenoid (length \(l\), radius \(a\), \(n_1\) turns per unit length) lies concentrically inside
@@ -1687,7 +1687,7 @@ Inductance: measured in {\bf henries} (\(H\)). \(H = V s/A\).
-
+
\paragraph{Example 7.11:} find self-inductance of toroidal coil with
rectangular cross-section (inner radius \(a\), outer radius \(b\), height \(h\))
@@ -1714,7 +1714,7 @@ Total flux: \(N\) times this, so self-inductance is
Inductance (like capacitance) is intrinsically positive. Use Lenz law. Think of {\bf back EMF}.
-
+
\paragraph{Example 7.12:} circuit with inductance \(L\), resistor \(R\) and battery \({\cal E}_0\).
What is the current ?
@@ -1753,7 +1753,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_Fl_ief.html b/build/emd_Fl_ief.html
index 6065345..9bd61af 100644
--- a/build/emd_Fl_ief.html
+++ b/build/emd_Fl_ief.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1621,7 +1621,7 @@ law in integral form:
-
+
{\bf Example 7.7:}
\({\bf B}(t)\) points up in circular region of radius \(R\). What is the induced \({\bf E}(t)\) ?
@@ -1629,7 +1629,7 @@ law in integral form:
amperian loop of radius \(s\), apply Faraday:
\[
\oint {\bf E} \cdot d{\bf l} = E (2\pi s) = -\frac{d\Phi}{dt} = -\pi s^2 \frac{dB}{dt}
- \Rightarrow {\bf E} = -\frac{s}{2} \frac{dB}{dt} \hat{\boldsymbol \phi}.
+ \Rightarrow {\bf E} = -\frac{s}{2} \frac{dB}{dt} \hat{\boldsymbol \varphi}.
\]
Increasing \({\bf B}\): clockwise (viewed from above) \({\bf E}\) from Lenz.
@@ -1637,7 +1637,7 @@ Increasing \({\bf B}\): clockwise (viewed from above) \({\bf E}\) from Lenz.
-
+
{\bf Example 7.8:} wheel or radius \(b\) with line charge \(\lambda\) on the rim.
Uniform magnetic field \({\bf B}_0\) in central region up to \(a < b\),
@@ -1646,7 +1646,7 @@ pointing up. Field turned off. What happens ?
Faraday:
\[
\oint {\bf E} \cdot d{\bf l} = -\frac{d\Phi}{dt} = - \pi a^2 \frac{dB}{dt}
- \Rightarrow {\bf E} = -\frac{a^2}{2b} \frac{dB}{dt} \hat{\boldsymbol \phi}.
+ \Rightarrow {\bf E} = -\frac{a^2}{2b} \frac{dB}{dt} \hat{\boldsymbol \varphi}.
\]
Torque on segment \(d{\bf l}\): \(|{\bf r} \times {\bf F}| = b \lambda E dl\).
Total torque:
@@ -1671,7 +1671,7 @@ called the {\bf quasistatic} approximation, and works provided we deal with
'slow enough' phenomena.
-
+
{\bf Example 7.9:} infinitely long straight wire carries \(I(t)\). Find
induced \({\bf E}\) field as a function of distance \(s\) from wire.
@@ -1719,7 +1719,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
diff --git a/build/emd_Me_dc.html b/build/emd_Me_dc.html
index fa28e02..6e8e452 100644
--- a/build/emd_Me_dc.html
+++ b/build/emd_Me_dc.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1607,7 +1607,7 @@ the continuity equation as
\]
The extra term would thus be eliminated if we were to put
-
The angular momentum of EM fields is directly given by
-
+
{\bf Angular momentum of EM fields}
\[
@@ -1630,7 +1630,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_ce_ce.html b/build/emd_ce_ce.html
index c354912..394fa7c 100644
--- a/build/emd_ce_ce.html
+++ b/build/emd_ce_ce.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1619,7 +1619,7 @@ This means that
\]
Since this is true for any volume, we have (re)derived the
-
diff --git a/build/emd_ce_mom.html b/build/emd_ce_mom.html
index 0c09c19..827009c 100644
--- a/build/emd_ce_mom.html
+++ b/build/emd_ce_mom.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1612,7 +1612,7 @@ in which the first integral can be interpreted as the momentum stored in the EM
This is thus simply a conservation law for momentum, with
-
+
{\bf Momentum density in the EM fields}
\[
@@ -1624,7 +1624,7 @@ This is thus simply a conservation law for momentum, with
In a region in which the mechanical momentum is not changing due to external influences, we then have the
-
+
{\bf Continuity equation for EM momentum}
\[
@@ -1653,7 +1653,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_ce_mst.html b/build/emd_ce_mst.html
index 450f4c6..15e712a 100644
--- a/build/emd_ce_mst.html
+++ b/build/emd_ce_mst.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1654,7 +1654,7 @@ and similarly for \({\boldsymbol B}\). We thus get
This expression can be greatly simplified by introducing the
-
+
{\bf Maxwell stress tensor}
\[
@@ -1677,7 +1677,7 @@ The element \(T_{ij}\) represents the force per unit area in the $i$th direction
We then obtain
-
+
{\bf EM force per unit volume}
\[
@@ -1689,7 +1689,7 @@ We then obtain
where \({\boldsymbol S}\) is the Poynting vector. Integrating, we obtain the
-
+
{\bf Total force on charges in volume}
\[
@@ -1718,7 +1718,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_ce_poy.html b/build/emd_ce_poy.html
index 690101d..27c8d9a 100644
--- a/build/emd_ce_poy.html
+++ b/build/emd_ce_poy.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1666,7 +1666,7 @@ so we get
Substituting this in \ref{Gr(8.6)} and using the divergence theorem,
we obtain
-
+
{\bf Poynting's theorem}
\[
@@ -1691,7 +1691,7 @@ energy is carried by EM fields out of \({\cal V}\) across its boundary surface.
Energy per unit time, per unit area carried by EM fields:
-
+
{\bf Poynting vector}
\[
@@ -1704,7 +1704,7 @@ Energy per unit time, per unit area carried by EM fields:
We can thus express Poynting's theorem more compactly:
-
+
{\bf Poynting's theorem}
\[
@@ -1717,7 +1717,7 @@ We can thus express Poynting's theorem more compactly:
where we have defined the total
-
+
{\bf Energy in electromagnetic fields}
\[
@@ -1740,7 +1740,7 @@ Then,
\]
so we get the
-
+
{\bf Poynting theorem (differential form)}
\[
@@ -1757,7 +1757,7 @@ and has a similar for to the continuity equation
-
+
\paragraph{Example 8.1} Current in a wire: Joule heating. Energy per unit time delivered to wire: from Poynting.
Assuming that the field is uniform, the electric field parallel to the wire is
@@ -1767,11 +1767,11 @@ Assuming that the field is uniform, the electric field parallel to the wire is
where \(V\) is the potential difference between the ends ald \(L\) is the length. Magnetic field is circumferential:
wire of radius \(a\),
\[
- {\boldsymbol B} = \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol \phi}
+ {\boldsymbol B} = \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol \varphi}
\]
Poynting:
\[
- {\boldsymbol S} = \frac{1}{\mu_0} \frac{V}{L} \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol x} \times \hat{\boldsymbol \phi} = -\frac{VI}{2\pi a L} \hat{\boldsymbol s}
+ {\boldsymbol S} = \frac{1}{\mu_0} \frac{V}{L} \frac{\mu_0 I}{2\pi a} \hat{\boldsymbol x} \times \hat{\boldsymbol \varphi} = -\frac{VI}{2\pi a L} \hat{\boldsymbol s}
\]
and points radially inwards. Energy per unit time passing surface of wire:
\[
@@ -1802,7 +1802,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
@@ -1650,7 +1650,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_emw_ep.html b/build/emd_emw_ep.html
index c1cf235..e1c0f6a 100644
--- a/build/emd_emw_ep.html
+++ b/build/emd_emw_ep.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1628,7 +1628,7 @@ so for a monochromatic EM plan wave,
\]
or more succinctly:
-
+
{\bf Poynting vector of a monochromatic EM wave}
\[
@@ -1644,7 +1644,7 @@ This has a transparent physical interpretation: the energy density \(u\) flows w
Similary, we get the
-
+
{\bf Momentum density of a monochromatic EM wave}
\[
@@ -1695,7 +1695,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_emw_mpw.html b/build/emd_emw_mpw.html
index ca73c1b..8cc5467 100644
--- a/build/emd_emw_mpw.html
+++ b/build/emd_emw_mpw.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1629,7 +1629,7 @@ B_0 = \frac{k}{\omega} E_0 = \frac{1}{c} E_0.
Generalizing to propagation in the direction of an arbitrary wavevector
\({\boldsymbol k}\) and (transverse) polarization vector \(\hat{\boldsymbol n}\), we have the
-
+
{\bf E and B fields for a monochromatic EM plane wave}
\[
@@ -1673,7 +1673,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
Author: Jean-Sébastien Caux
-
Created: 2022-02-13 Sun 21:20
+
Created: 2022-02-14 Mon 20:35
diff --git a/build/emd_emw_we.html b/build/emd_emw_we.html
index 828c8e0..2e24f76 100644
--- a/build/emd_emw_we.html
+++ b/build/emd_emw_we.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1626,7 +1626,7 @@ These take the form of coupled first-order partial differential equations for \(
Since \({\boldsymbol \nabla} \cdot {\bf E} = 0\) and \({\boldsymbol \nabla} \cdot {\bf B} = 0\),
we get the
-
+
{\bf Wave equations for electric and magnetic fields in vacuum}
\[
@@ -1682,7 +1682,7 @@ target="_blank">Creative Commons Attribution 4.0 International License.
diff --git a/build/emdm_Me_Mem.html b/build/emdm_Me_Mem.html
index c15aaeb..2ccb94c 100644
--- a/build/emdm_Me_Mem.html
+++ b/build/emdm_Me_Mem.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1633,7 +1633,7 @@ dI = \frac{\partial \sigma_b}{\partial t} da_{\perp} = \frac{\partial P}{\partia
\]
We therefore have the
-
+
{\bf Polarization current density}
\[
@@ -1651,7 +1651,7 @@ the polarization current is the result of linear motion of charge when
polarization changes). We can check consistency with the continuity equation
associated to the conservation of bound charges: