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An overview of electromagnetism, including topics such as electricity, magnetism, capacitors, and Maxwell's equations. It includes equations and formulas related to each topic, as well as explanations of key concepts. The document also provides tips for taking the GRE in SI units and notes on differences in Maxwell's equations. It could be useful as study notes or a summary for students studying electromagnetism.
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General comments: the GRE is in SI units, so for those who took 8.022, make sure to
pay attention to where the epsilons and mus go. (And thus the slightly different form of
Maxwell’s Equations.)
Also, on one of the practice tests I looked at, they asked about which if Maxwell’s equa-
tions would need to be modified to account for magnetic monopoles.
Work:
W
q 0
has units of volts. Volt = Joules/Coulomb.
1.1 Electricity
k =
1
4 πε 0
[Nm
2 C
− 2 ], ε 0
is permittivity of free space
F = k
q 1
q 2
d
2
Force between two charges
F = q 1 E Force on charge in field
E = 4πk
Q
A
Uniform electric field between two charged parallel plates, each of area A
E = k
q
−→ r
r
2
r in direction + → -. Electric field of single charge.
W
q
= Ed Electric potential
V = IR Ohm’s
2 R Power
R = ρ
l
A
Resistivity
tot
1
2
1
Rtot
1
R 1
1
R 2
1.2 Magnetism
Eq + ~vq ×
B Lorentz Force Law
l + ×
B Force on current carrying conductor
Φ
A
Magnetic induction, Φ=magnetic flux
mv
Bq
Radius of curvature of moving charge in magnetic field
μ 0
4 π
q
−→ v ×br
r
2
Magnetic field of moving charge
B · dl = μ 0
I Ampere’s law, use for calculating current
1.3 Capacitors
Q
V
= ε 0
A
d
Capacitance, Q = charge on either plate. [farads]
C
1
2
2 Energy of Capacitor
Q
ε 0 A
d
Capacitors in series (or multiple different dielectrics): C =
1 “
1
C 1
”
“
1
C 2
”
Charging: q = (Cε)
1 − e
−t/RC
Discharging: q = (Cε)
e
−t/RC
1.3.1 Undriven
RL Circuit: V R
L
dI
dt
I(t) = I 0
e
−Rt/L
RC Circuit: V (t) = V 0
e
−t/RC
1.3.2 Driven RLC Circuit
V (t) = V f
︸︷︷︸
forced response
S 1 t
S 2 t
natural response
Where S 1 , 2
= −α ±
α
2 − ω
2
0
α =
1
2 RC
, ω 0
1 √
LC
1.4 Maxwell’s Equations
Gauss’s Law
ρ
ε 0
Gauss’s law for magnetism
Faraday’s law
∂
~ B
∂t
Ampere’s Law
B = μ 0
J + μ 0
ε 0
∂
~ E
∂t
J is the total current density.
1.5 Magnetic and electric fields in matter
ε = ε 0 εr for media other than free space, where εr = relative permitivity of the media.