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Physics GRE > E&M > Flashcards

E&M Flashcards

1
Q

Columb’s law

A

Fe = ke*|q1|*|q2|/r2

ke = columb constant

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2
Q

Columb’s constant

A

ke = 1/(4*π*ϵ0)

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3
Q

Force of Electrical feild

A

Fe=qE

force that acts on a point charge

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4
Q

direction of electrical field lines

A

positive charge to negative charge

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5
Q

acceleration of particle in uniform electrical field

A

a = qE/m

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6
Q

Electric Flux

A

ΦE = EAcos(θ)

θ = angle between direction electrical field and normal of area

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7
Q

Gaussian surface

A

closed surface containing charge

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8
Q

Net flux through gaussian surface

A

ΦE = E∮dA = q/ϵ0

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9
Q

potential energy of electric feild

A

ΔU = -q0 ∫ Eds

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10
Q

Electric potential

A

V = U/q0

ΔV = ΔU/q0 = - ∫ E·ds

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11
Q

Work done on charge in electric field

A

W = qΔV

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12
Q

Electric potential in uniform electric field
*how does electric field increase/decrease?*

A

ΔV = -Ed

electric field lines point in direction of decreasing electric potential

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13
Q

electric potential from point charge

A

V = ke*q/r

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14
Q

relationship between equipotential surfaces and electric field lines

A

equipotential surfaces must be perpendicular to electric field lines

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15
Q

electric potential due to continuous charge distribution

A

V = ke ∫dq/r

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16
Q

electric potential at surface of charged coductor

A

every point on surface of charged cuductor is at the same electric potential

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17
Q

Electric field within charged conductor

A

electric field inside cavity must be 0

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18
Q

Capacitence definition

A

C = Q/ΔV

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19
Q

Capicitence of a charged sphere

A

Q/ΔV = Q/(keQ/R) = R/ke = 4πϵ0R

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20
Q

Capicitance of parallel-plate capacitor

A

C = ϵ0A/d

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21
Q

Capacitors in parallel

A

Ctot = C1 + C2 + C3 …

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22
Q

Capacitors in series

A

1/Ctot = 1/C1 + 1/C2 + 1/C3 ….

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23
Q

Energy stored in capacitor

A

U = Q2/2C = 1/2*QΔV = 1/2*C(ΔV)2

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24
Q

Energy density

A

uE = U/Ad

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25
Q

Capacitance with dielectric

A

C = ϰC0

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26
Q

Voltage with dielectric

A

V = ϰV0

note: if voltage source is not turned off when dielectric is inserted, voltage will remain the same

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27
Q

Definition of current

A

I = ΔQ/Δt

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28
Q

Current density

A

J = I/A = nqvd

J = σE
σ -> is the coductivity of the conductor. (Ohm’s law)

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29
Q

Definition of resistance

A

R = ΔV/I

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30
Q

resistivity

A

ρ = 1/σ

R = ρ*l/A

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31
Q

temperature coeffecient of resistivity

A

α = (1/ρ0)*(Δρ/ΔT)

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32
Q

resistance at temperature

A

R = R0[1+α(T - T0)]

33
Q

Power in resister

A

P = IΔV
P = I2R
P = (ΔV)2/R

34
Q

Voltage in battery

A

ΔV = ε - Ir

ε -> emf (max possible voltage battery can provide between terminals)
r -> internal resistance of battery

35
Q

Resistors in series

A

Rtot = R1 + R2 + R3 …

36
Q

Resistors in Parallel

A

1/Rtot = 1/R1 + 1/R2 + 1/R3 …

37
Q

Kirchof’s rules

A

1) Junction rule: sum of currents entering any junction in a circuit must equal the sume of the curents leaving that junction
2) Loop rule: The sum of potential differences across all elements around any closed loop circuit must be 0

38
Q

RC circuit, using loop

A

ε - q/C - IR = 0

ε -> voltage on battery

39
Q

Initial current of RC circuit

A

I0 = ε/R

40
Q

maximum charge on capacitor in RC circuit

A

Q = Cε

41
Q

charge as a function of time in charging RC circuit

A

q(t) = Cε(1 - e-[t/RC]) = Q(1 - e-[t/RC])

42
Q

current as a function of time in charging RC circuit

A

I(t) = (ε/R)e-t/RC

43
Q

charge as a function of time for discharging capacitor in RC circuit

A

q(t) = Qe-t/RC

44
Q

current as a function of time for discharging RC circuit

A

I(t) = -(Q/RC)e-t/RC

45
Q

Galvanometer

A
  • measures current and voltage
  • uses torque of magnetic field generated from coil
  • connect in series to measure voltage
  • connect in parallel to measure current
46
Q

Ammeter

A
  • measures current
  • should ideally have 0 resistance
  • connect in series
47
Q

Voltmeter

A
  • measures voltage
  • ideally has infinite resistance
  • connect in parallel
48
Q

direction of magnetic field lines

A

north to south

49
Q

force on charged particle in magnetic field

A

FB = qv x B = |q|vBsinθ

θ -> angle between v and B

50
Q

Magnetic force on current carrying wire

A

FB = ILxB

51
Q

symbol for magnetic feild out of page

A

•

52
Q

symbol for magnetic field into page

A

x

53
Q

Right hand rule

A
54
Q

magnetic force from closed current carrying loop in magnetic field

A

FB = 0

55
Q

magnetic force on curved current carrying wire

A

equal to a straight wire connected to end points carrying the same current

56
Q

maximum torque on current carrying loop in magnetic field

A

τmax = IAB

57
Q

torque of current carrying wire in magnetic field

A

τ = IAxB = IABsinθ

θ -> angle of magnetic field B and normal of area

58
Q

radius of motion of charged particle in magnetic field

A

r = mv/qB

59
Q

velocity selector for electric and magnetic field

A

qE = qvB

v = E/B

60
Q

Biot-Savart law

A

dB = [μ0/4π][I*ds x r/r2]

61
Q

magnetic field from current in infinite long wire

A

B = μ0I/2πr

62
Q

magnetic force between 2 parallel wires

A

Fb/L = μ0I1I2/2πa

63
Q

Ampere’s law

A

∮B•ds = μ0I

64
Q

magnetic field inside radius of conductor

A

B = (μ0I/2πR2)r

(linear)

65
Q

magnetic field of solenoid

A

B = μ0(N/L)I = μ0nI

  • N -> numer of turns*
  • L -> length*
  • n -> N/L*
66
Q

Magnetic flux

A

ΦB = BAcosθ

67
Q

Gauss’s law for magnetism

A

∮BdA = 0

magnetic flux through a closed surface is always 0

68
Q

Faraday’s law of induction

A

V = -dΦB/dt

69
Q

direction of current from enduced emf (lenz’s law)

A

magnetic field from current must oppose the change of magnetic field from the magnet

70
Q

emf for AC generator

A

ε = NABωsin(ωt)

71
Q

Maxwell’s equations

A

∮EdA = q/ε0

∮BdA = 0

∮Eds = -dΦB/dt

∮Bds = μ0I +μ0ε0dΦE/dt

72
Q

self induced emf in inductor

A

εL = -LdI/dt

73
Q

Kirchof Loop for RL circuit

A

ε - IR - LdI/dt = 0

74
Q

current in RL circuit

A

I = ε/R(1 - e-[Rt/L])

75
Q

Energy stored in inductor

A

U = (1/2)LI2

76
Q

Total energy stored in LC circuit

A

U = UC + UL = Q2/2C + (1/2)LI2

77
Q

charge as function of time for LC circuit

A

Q = Qmaxcos(ωt + φ)

78
Q

Current as a function of time for LC circuit

A

I = ωQmaxsin(ωt + φ)

79
Q

Electric field from continuous charge distribution

A

E = ke*Int(dq/r2)

Physics GRE (9 decks)

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