Electromagnetism Flashcards
Equation for current.
I = dq/dt
Coulomb’s law.
F = k Q1Q2/(r^2)
How does Coulomb’s law change for vector?
Multiply by vector r^
How can the force on a charge be found from two close point charges?
Using superposition principle.
Equation for electric field.
E=F/q
E and F are vectors.
How can electric fields from point charges be combined?
Using superposition principle.
Dipole moment equation
p=qa
p is vector
a is vector from negative to positive
Derive equations for electric field parallel and perpendicular to the dipole axis.
Check derivation.
Derive equation for electric field of a dipole in a general position.
Check derivation.
By superposition, derive the field from an infinite plane of uniform charge distribution.
Check derivation.
Flux equation
Flux = ∫E.dS
Gauss’s Theorem
Sum(charge)/ε0 = ∫E.dS
Easy geometries for Gauss’s Theorem
Field perpendicular to surface and same value at all positions on surface.
Field parallel to surface (E.dS=0)
Work done moving charge in electric field
W=-q ∫E.dl
As dW=F.dl
and F=-qE when external force is applied
Work done moving charge through closed loop
=0
Due to conservative nature of electric field
Derive an expression for potential energy of a dipole in an E-field.
Check derivation
How can the potential from two point charges be found?
Using superposition.
How to find E from V?
Partially differentiate V to give E in a certain direction.
E=-gradV
How are equipotentials distributed in a conductor?
There is no potential difference in a conductor thus a conductor carrying static charge is an equipotential volume with an equipotential surface.
Definition of capacitance.
Ratio of charge to potential
q=CV
Energy stored in a capacitor equation.
dW=Vdq
W = ∫Vdq = QV/2
Equation for εr
εr=Cd/C0
Capacitence with dielectric to capacitance without.
Define electric polarisation
Dipole moment per unit volume
Total E field in presence of dielectric
E=E0+Ep