\({\boldsymbol \nabla} \cdot ({\boldsymbol \nabla} T) \equiv {\boldsymbol \nabla}^2 T\) 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/c_m_ic_gauss.html b/build/c_m_ic_gauss.html
index 398e609..07747cc 100644
--- a/build/c_m_ic_gauss.html
+++ b/build/c_m_ic_gauss.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1612,6 +1612,8 @@ This is know either as Gauss' theorem, Green's theorem or the d
+
diff --git a/build/d_emd.html b/build/d_emd.html
index 8f9ebad..43556b5 100644
--- a/build/d_emd.html
+++ b/build/d_emd.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1628,6 +1628,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_emd_ce.html b/build/d_emd_ce.html
index ea8e504..d7e9225 100644
--- a/build/d_emd_ce.html
+++ b/build/d_emd_ce.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1623,6 +1623,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_emd_emw.html b/build/d_emd_emw.html
index a07c838..5bbfe2a 100644
--- a/build/d_emd_emw.html
+++ b/build/d_emd_emw.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1626,6 +1626,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_emf.html b/build/d_emf.html
index 90c8676..772b1aa 100644
--- a/build/d_emf.html
+++ b/build/d_emf.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1623,6 +1623,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_ems.html b/build/d_ems.html
index 0cebd8f..70566ff 100644
--- a/build/d_ems.html
+++ b/build/d_ems.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1645,6 +1645,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_ems_ms.html b/build/d_ems_ms.html
index 4670f93..160828f 100644
--- a/build/d_ems_ms.html
+++ b/build/d_ems_ms.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1625,6 +1625,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_emsm.html b/build/d_emsm.html
index 0185289..1faaf48 100644
--- a/build/d_emsm.html
+++ b/build/d_emsm.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1628,6 +1628,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_emsm_msm.html b/build/d_emsm_msm.html
index efc93f1..822a4af 100644
--- a/build/d_emsm_msm.html
+++ b/build/d_emsm_msm.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1626,6 +1626,8 @@ As a strict minimum, you should be able to:
+
diff --git a/build/d_m.html b/build/d_m.html
index 5167f4c..f7f2770 100644
--- a/build/d_m.html
+++ b/build/d_m.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1636,6 +1636,8 @@ Things you should be able to do (ideally: from scratch, on a blank sheet of pape
+
diff --git a/build/d_red.html b/build/d_red.html
index b80a386..5dffa11 100644
--- a/build/d_red.html
+++ b/build/d_red.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1630,6 +1630,8 @@ As a strict minimum, you should be able to:
diff --git a/build/emd_Fl_Fl.html b/build/emd_Fl_Fl.html
index c386afc..4b295c1 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)
\[
@@ -1700,6 +1700,8 @@ to an opposing counter-reaction.
+
diff --git a/build/emd_Fl_e.html b/build/emd_Fl_e.html
index dbb1b2f..a4cd06a 100644
--- a/build/emd_Fl_e.html
+++ b/build/emd_Fl_e.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1657,7 +1657,7 @@ W = \frac{1}{2\mu_0} \left[ \int_{\cal V} d\tau B^2 - \int_{\cal V} d\tau {\bold
\]
We can integrate over all space: after neglecting boundary terms (assuming fields fall to zero at infinity), we are left with
-
\paragraph{Example 7.13:} coaxial cable (inner cylinder radius \(a\), outer \(b\)) carries current \(I\).
Find energy stored in section of length \(l\).
@@ -1702,6 +1702,8 @@ Note: gives easy way to find inductance, since \(W = \frac{1}{2} L I^2\).
\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 ?
@@ -1738,6 +1738,8 @@ where \(\tau \equiv L/R\) is the {\bf time constant} of the circuit.
+
diff --git a/build/emd_Fl_ief.html b/build/emd_Fl_ief.html
index 4ca544b..6065345 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 \({\bf E}(t)\) ?
@@ -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 \(a < b\),
@@ -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.
@@ -1704,6 +1704,8 @@ Reason: in this case, we've overstepped the quasistatic limit. We need
+
diff --git a/build/emd_Me_dc.html b/build/emd_Me_dc.html
index 70ddd53..fa28e02 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
-
diff --git a/build/emd_ce_ce.html b/build/emd_ce_ce.html
index 6965d77..c354912 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
-
+
{\bf Continuity equation}
\[
@@ -1645,6 +1645,8 @@ imposes a functional constraint on these sources: not {\it any} \(\rho\) and
+
diff --git a/build/emd_ce_mom.html b/build/emd_ce_mom.html
index 023a93b..0c09c19 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}
\[
@@ -1638,6 +1638,8 @@ In a region in which the mechanical momentum is not changing due to external inf
+
diff --git a/build/emd_ce_poy.html b/build/emd_ce_poy.html
index 41c8b1d..690101d 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)}
\[
@@ -1757,7 +1757,7 @@ and has a similar for to the continuity equation
-
+
\paragraph{Example 8.1} Current in a wire: Joule heating. Energy per unit time delivered to wire: from Poynting.
Assuming that the field is uniform, the electric field parallel to the wire is
@@ -1787,6 +1787,8 @@ and the value is as expected.
+
diff --git a/build/emd_emw_ep.html b/build/emd_emw_ep.html
index fca0c76..c1cf235 100644
--- a/build/emd_emw_ep.html
+++ b/build/emd_emw_ep.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1628,7 +1628,7 @@ so for a monochromatic EM plan wave,
\]
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}
\[
@@ -1680,6 +1680,8 @@ The {\it radiation pressure} is the momentum transfer per unit area per unit of
diff --git a/build/emd_emw_mpw.html b/build/emd_emw_mpw.html
index fa31848..ca73c1b 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}
\[
@@ -1658,6 +1658,8 @@ or if you prefer explicit real parts (adding a possible phase shift \(\delta\)):
+
diff --git a/build/emd_emw_we.html b/build/emd_emw_we.html
index c97e01e..828c8e0 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}
\[
@@ -1667,6 +1667,8 @@ the actual electric and magnetic fields are given by the real part.
+
diff --git a/build/emdm_Me_Mem.html b/build/emdm_Me_Mem.html
index a01206c..c15aaeb 100644
--- a/build/emdm_Me_Mem.html
+++ b/build/emdm_Me_Mem.html
@@ -1,7 +1,7 @@
-
+
Pre-Quantum Electrodynamics
@@ -1633,7 +1633,7 @@ dI = \frac{\partial \sigma_b}{\partial t} da_{\perp} = \frac{\partial P}{\partia
\]
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: