Update lecture notes EE1P1

This commit is contained in:
Folkert Kevelam 2026-02-17 12:13:06 +01:00
parent b8bdc10fc1
commit 4a08f4b377

View File

@ -62,3 +62,109 @@
=== Spherical coordinates
+ EE1M1: $r, theta, phi$, EE1P1: $rho, phi, theta$
= Lecture 2
= Seminar 1 - Coulomb force
== Coulomb force
Force between two charges:
$
&arrow(F)_(S O)(arrow(r)_(S O), Q_S, Q_O) = k (Q_S Q_O) / r_(S O)^2 hat(r)_(S O) \
&arrow(r)_(S O) = arrow(r)_O - arrow(r)_S \
&r_(S O) = |arrow(r)_(S O)| = |arrow(r)_O - arrow(r)_S| \
&hat(r)_(S O) = arrow(r)_(S O) / r_(S O) \
&k = 10^(-7) c_o^2 approx 8.99 dot 10^9 "N sym.dot m"
$
= Lecture 3
*polarisation* is when an electrical field is applied to a dielectric, which
causes the dipoles within the dielectric to orient to the same point, along
the external electric field.
= Lecture 4 - Gauss's law
== Gauss's law in integral form
Based on the idea of *flux*:
- *flux* is the idea of how much of "something" crosses a given surface
- The *electrostatic field* does not cross anything (it was originally believed to)
The electric flux can be calculated using the surface integral of the electric field.
#definition[
electric flux:
$
Phi = integral_cal(S) arrow(E) dot d arrow(A) = integral_S E cos(theta) d A
$
for a uniform field and a flat surface:
$
Phi = integral_cal(S) arrow(E) dot d arrow(A) = E A cos(theta)
$
]
#definition[
Gauss's law:
$
integral.cont_cal(C) arrow(E) dot d arrow(A) = q_("enclosed") / epsilon_0
$
Gauss's law in a medium:
$
integral.cont_cal(C) dot d arrow(A) = q_("enclosed") / (epsilon_0 epsilon_r)
$
]
assuming that homogenisation is applicable. \
Gauss's law is useful for calculating the electric field in symmetric configurations:
- spherical symmetry
- cylindrical symmetry
- symmetry with respect to a plane
$
arrow(E)(arrow(r)) = arrow(E)(r, theta, phi) \
arrow(E)(arrow(r)) = E_r hat(r) \
$
*Two distinct cases*:
+ Observation point is inside the surface.
with a sphere, with a uniform charge density the total charge is:
$
Q_("tot") = rho (4/3) pi R^3
$
+ Observation point is outside the surface.
=== Examples
==== Calculating the electric field in a sphere with a single charge
==== uniformly charged rod
== Conditions at the surface of perfect conductors
== Local form of Gauss's law
- The function describing $arrow(E)$ is continuously differentiable.
- the medium can be taken as "continuous" (homogenisation).
#definition[
Gauss's law in local-form:
$
arrow(nabla) dot arrow(E)(arrow(r)) = rho(arrow(r)) / epsilon_0
$
]