Week 7 Capacitance, Relative Permittivity & Dielectrics Flashcards
define capacitance
ratio between the charge and potential difference
what is the parallel plate capacitor equation
C = Q / ΔV = ε0A / d
what is capacitance measured in
Farads
F
what is the energy of a parallel plate capacitor
U = 1/2 C(ΔV)^2
what happens when the capacitor is disconnected from a battery
the voltage drops and capacitance increases
what is the relative permittivity equation
εr = C / Cvac
briefly describe dielectics
electrical insulators but in the presence of an external electrical field the intrinsic dipoles align
what is the electric dipole moment equation
p = qd
what is the external electric dipole energy equation
-p * Eext
what is the external electric dipole torque equation
τ = p x Eext
why do dipoles align
to minimise energy to eliminate torque
what is the polarisation equation
P = np
P is polarisation
n is the number density
p is the mean dipole moment
what is the linear isotropic polarisation equation
P = χε0E
χ is the electric susceptibility
what are the two types of the polarisation
alignment of intrinsic dipoles
dipoles are induced
what is the aligned polarisation equation
Palign = (np^2 / 3kT) Eext
