Electrostatics, Electricity, and Magnetism Flashcards
what is the value of the elementary charge? of a proton or electron
e = 1.6 x 10 ^ -19
+ for proton - for electron
Coulomb’s law for 2 point charges
F = kQq/r^2
Coulomb’s constant
k = 9 x 10 ^9 Nm^2/c^2
Electric field strength (E)
E = kQ/r^2
Q=charge producing the field
Electric force formula
F = qE
Formula for coulomb’s law = N
Electric potential formula for point charges
φ = kQ/r
in V, scalar
Change in electric potential
ΔPE = qΔφ = qV
in J
work done by an electric field
W = -ΔPE
change in kinetic energy for an electric field
ΔKE = -ΔPE
current formula
I = Q/t
in A
Resistance formula
R = pL/A
Ohm’s law
V=IR
Resistors in series (and current/voltage)
R = R1 + R2 …
current is constant, voltage adds up
Resistors in parallel (and current/voltage)
1/R = 1/R1 + 1/R2 … or R = R1R2/R1+R2
voltage is constant, current in parallel should equal current entering
power for circuit
P=IV
P=I^2R
P=V^2/R
note: the ground is at potential 0.
root mean square for AC circuits
Vrms = Vmax/√2 Irms = Imax/√2
average power for AC circuit
P = (Irms)^2R P = Irms (Vrms)
charge on parallel plate capacitors
Q=CV
capacitance formula
C = εA/d
capacitance formula with dielectric
Cwith = KCwithout = KεA/d
electric potential for parallel plate capacitor
V=Ed
E=V/m or N/C, same thing!
stored potential energy in a capacitor
PE = 1/2QV = 1/2CV^2 = 1/2Q^2/C
work done by battery to charge a capacitor
W = PE
capacitors in series
1/C = 1/C1 + 1/C2… or C=C1C2/C1+C2
charge is the same across capacitors
capacitors in parallel
C = C1 + C2 ….
voltage is the same across capacitors
magnetic force on a moving charge
Fb = |q| vBsinθ θ = angle btw v and B
B created by a long straight wire
B ~ I/r
B created by a solenoid
B ~ IN/L
L = length of solenoid, N = number of coils
What is the direction that magnetic field lines for a bar magnet point
North to South
- north pole will want to line up with external magnetic field (south pole opposite)
Which end of the battery is positive in a circuit?
the longer one
Energy for a circuit
Energy = Power(time)
in J
How to find terminal voltage
V = ε - Ir V = terminal voltage (real voltage when internal resistance is taken into account) ε = emf (the original voltage) I = current (total) r = internal resistance
what are the 2 purposes of a capacitor
1) create a uniform electric field (V=Ed)
2) store electric potential energy (PE=1/2QV etc)
Force for a capacitor
F=qE
Properties of a capacitor when dielectric is added after disconnecting it from battery
C increases always and Q stays the same.
- V d. by K (Q=CV)
- E d. by K (V=Ed)
- PE d. by K (1/2QV)
Properties of a capacitor when dielectric is added before disconnecting it from battery
C increases always and Q increases by K.
- V stays the same (Q=CV)
- E stays the same (V=Ed)
- PE increases by K (1/2QV)
work done by magnetic force
Magnetic force does no work on the particle because it does not change the speed of the particle, only the direction.
