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Flashcards in Electricity and Magnetism Deck (143):
1

Electrical current is defined as what?

charge per unit time
I=Q/t, Q=coulombs t=seconds

2

Atom with net charge of either positive or negative

Ion

3

Negative ion

Anion

4

Positive Ion

Cation

5

The force required to move charges in a material

Voltage

6

Different names for voltage

Electromotive force(emf), Potential Difference

7

Volts formulas

V=W/C

W=work, Joules
C=Charge, Coulombs
*1 volt = 1 Joule/Coulomb

8

opposition or hindrance offered by the material to current flowing

Resistance

9

Ohm is named after whom?

Georg Simon Ohm

10

Resistance Formula

R=pL/A

p=resistivity
L=length
A=cross sectional area

11

What is the equivalent if 1 mil?

1/1000 inch

12

A Square mil is equal to?

pi/4 circular mil

13

Temperature effect on resistance formula

R2/R1=(|T|+t2)/(|T|+t1)
R2=R1(1+α(t2-t1))
α=1/(|T|+t1)

α=temperature coefficient of resistance at t1
T=inferred absolute zero temp
-234.5 for annealed copper

14

the property of material to aid or allow the flow of charge

Conductance

15

Conductance Formula

G=1/R
G=A/pL

16

Amount of work done in a circuit per unit time

Electrical Power

17

Power formulas

P=W/t
P=QV/t
P=IV
P=V^2/R
P=I^2R

18

What are the common resistivity(ρ) of:
Aluminum,

ρ = 2.6 x10^-8 ohm-m

19

What are the common resistivity(ρ) of:
Brass,

ρ = 6 x10^-8 ohm-m

20

What are the common resistivity(ρ) of:
Carbon,

ρ = 350 x10^-8 ohm-m

21

What are the common resistivity(ρ) of:
Nichrome,

ρ = 100 x10^-8 ohm-m

22

What are the common resistivity(ρ) of:
Silver

ρ = 1.5 x10^-8 ohm-m

23

What are the common resistivity(ρ) of:
Tungsten

ρ = 5.6 x10^-8 ohm-m

24

Temperature resistance coefficient (α, Not thermal expansion) of:
Annealed copper

α20 = 0.00393

25

Temperature resistance coefficient(α, Not thermal expansion) of
Nickel

α20=0.006

26

Temperature resistance coefficient of(α, Not thermal expansion)
Iron

α20=0.0055

27

engineering prefix
nano

1x10^-9

28

engineering prefix
pico

1x10^-12

29

engineering prefix
femto

1x10^-15

30

engineering prefix
atto

1x10^-18

31

A substance that possesses magnetism property and can attract iron and other ferromagnetic materials including ferrites (non metallic ferromagnetic materials)

Magnet

32

The place where magnet was discovered

Magnesia

33

the magnet is called _____ by ancient people

Lodestar (early guiding stars)
Iron oxide called magnetite (Fe3O4)

34

It is produced by electric current rather than a natural magnet

Electromagnetism

35

Who discovered the phenomenon of electromagnetism?

Hans Christian Oersted (april 21, 1820)

36

A property possessed by magnetic materials by the virtue of which residual magnetism is possible

Retentivity

37

The magnetism left after the removal of the magnetizing force

Residual Magnetism

38

The opposite of retentivity

Coercivity

39

It is required to counter retentivity to eliminate residual magnetism

Coercive force

40

How can a magnet lose its properties?

Tax evasion. jk, When it is heated, hammered, or dropped from a height

41

Tractive/Lifting force of a magnet formula

F=.5(AB^2)/u0
A=total area of contact, m^2
B=flux density, Wb/m^2 or T`

42

What is the first law of magnetism

Like poles repel and unlike poles attract

43

What is the second law of magnetism

A magnetic field always tends to arrange itself that the greatest number of lines of force are created

44

What is the domain theory of magnetism

The magnetic property of a material is due to the electron's spin direction. In non-magnetic materials, the net magnetic field is zero since electron's spin cancels each other, while in magnetic materials the magnetic fields are aligned thus forming small bar magnet

45

What is the molecular/Weber theory of Magnetism?

The molecules of a material are magnets themselves and magnetization consists of rearrangement of the molecules in a way that all north poles point in the same direction, as such with the south pole

46

Magnetic fields originate in _______ and terminate in _________

North pole, South pole

47

What do you call the property when the magnetic flux spreads in the air?

Fringing

48

What is Coulomb's first law?

THe force of attraction or repulsion of two magnetic pole is directly proportional to their strength

49

What is Coulomb's second law?

The force of attraction between two poles is inversely proportional to the square of the distance between them

50

Formula of Magnetic attraction

F = km1m2/r^2

k=1/4pi(u)
u=uo*ur
ur=relative permittivity
uo=absolute permittivity (constant 33)

51

The tendency of the magnetic lines of force is to ____________

take an easy magnetic path

52

___(yes/no) lines of force can cross each other

no

53

where is the right hand rule applicable?

when determining the magnetic field(conventional current flow)

54

Formula for Force in a current carrying conductor in a magnetic field

F = BILsin(theta)

B=flux density, Wb/m^2 o Tesla
I=current flowing in a conductor, Ampere
L-length of conductor, meters

55

Formula for Magnitude of flux surrounding a straight conductor

phi=14x10^-8*I*L*log(R/r) Wb

I=current, A
L=length, ft
R=radius of the desired limiting cylinder
r=radius of the conductor

56

Formula for Magnitude of flux between two parallel conductors

phi=28x10^-8*I*L*log(d-r)/r Wb

d=distance between the conductors

57

Formula for Force between two parallel conductors

F=2I1*I2*L/d x10^-7

I1,I2 = current in the conductors
L= length of the conductors, Meters
d=distance between the conductors, Meters

58

Direction of force between two parallel conductors

If same current direction, force is Attractive
If different direction, Force is repulsive

59

Formula for Force of attraction between poles of magnets

F = km1m2/d^2 Newtons

k=1/4piu0 x10^-7
m1,m2= magnetic pole strength, Wb
d=distance between poles, meters

60

Formula for Magnetic Flux Density

B=Φ/A, Wb/m^2

Φ= magnetic flux lines (in Wb)
A= area (in m^2)

61

Reluctance Formula

R=L/uA, Ampere-turn/Wb
R=mmf/phi

L=length of the magnetic path, m
A=cross sectional area, m^2
u=permittivity of the material, H/m

62

Formula for Energy stored in a magnetic Circuit

1/2R(phi)^2

63

What is Hysteresis?

it is the internal friction of molecules, causing the heating of a material

64

What is Magnetomotive force?

The force required to establish magnetic field in a magnetic material

65

Magnetomotive force is dependent upon what?

Current flowing, A
and number of turns, Turns

66

1 Gilbert is equivalent to_____

0.4 (Ampere-Turn)

67

What is magnetizing force or magnetic field intensity?

magnetomotive force per unit length required to properly magnetize a given material

68

Formula for Magnetic field intensity formula?

H=mmf/L=NI/L ; (At/m)

69

It is the measure of how easily a magnetic field can be created in a material upon application of a magnetic force

Permeability (in Henrys per meter)

70

The reciprocal of permeability

Reluctivity

71

Hysteresis loss formula is also known as

Steinmetz's Formula

72

What is the formula for Hysteresis Loss

Wh=nfBm^1.6

n=hysteresis coefficient
f=frequency, Hz
Bm=Maximum flux density, T

73

Formula for Ohm's law in magnetism

phi=mmf/R ; Wb/Maxwell

74

The property of a magnetic material to allow easily magnetic flux to be established,

Permeance

75

Permeance Formula

1/R = Wb/At

76

Flux Density and Magnetic Field Intensity of an infinitely long straight conductor

B=uI/2pi*r
H=I/2pi*r

I - Current in conductor

77

Formulas for Ampere's Circuital law in magnetism

Source of mmf
mmf=NI

mmf drops:
mmf=phi*R
mmf=Hl

78

Total Reluctance in series

Rt=R1+R2+R3...

79

Total Reluctance in Parallel

1/Rt=1/R1+1/R2...

80

Total FLux in Series

Phi(total)=phi(1)=phi(2)=phi(3)

81

Total Flux in Parallel

Phi(total)=Phi1 + Phi2

82

Who discovered Charge?

Benjamin Franklin

83

Where and when was "electricity" coined?

600BC, Greece

84

"electricity" comes from the word _____

Amber

85

When you rub Silk on glass, the glass is (+ , - ) charged

Positively charged

86

Another term for a positively charged material

Vitreous

87

When you rub Fur on Rubber, the Rubber is (+ , - ) charged

Negatively Charged

88

Another term for a negatively charged material

Resinous

89

A machine used to produce a static charge

Van de Graff Generator

90

Coloumb's Constant(k)

K = 1/(4πεo) = 9 x 10^9 Nm^2/C^2

91

Unit of Coloumb's Constant (k)

Nm^2/C^2

92

Unit of Permittivity (ε)

C^2/(Nm^2)
or
F/m

93

The Electrostatic force is ____ times greater than the gravitational force of attraction felt by two particles

10^36

94

Unit of Electric Field Intensity

Volts / m or N / Coloumb
More common as V/m

95

A material that emits equally opposing charges

Dipole

96

an electric field emitted by a dipole will have a point, with an E-Field intensity equal to zero, Located at ________

Nowhere
(no point in an E-Field of a dipole exists an Intensity of zero)

97

The Force Vector and the E-Field Vector are always _________

Parallel to each other (points at the same direction

98

Gauss Law

Flux = ∑(Q / εo)

Q - Charges inside a closed surface

99

What is the E-Field observed when a Charge Q is Distributed uniformly on a spherical surface?

The E-Field observed at any point outside the sphere will look like an E-Field emitted by a charge in a single point, as if the charge was only concentrated at the center of that sphere

100

What is the E-Field observed inside a spherical surface with a uniformly distributed charge over its surface?

E-Field is 0
Charge(Q) inside is 0 as well

101

What is the E-Field observed in the presence of an infinite sheet of charge

Assuming that the sheet is infinitely large, the E-Field Intensity observed AT ANY POINT IN SPACE is:

E = ρs / 2εo

ρs - Surface Charge Density (Coloumb / m^2)
εo - Permittivity of Free Space

102

E-Field BETWEEN equally, but oppositely charged plates

E = ρs / εo

ρs - Surface Charge Density (Coloumb / m^2)
εo - Permittivity of Free Space

103

E-Field OUTSIDE equally, but oppositely charged plates

E = 0
(except at the ends of the plates, where the fringe field exists)

104

What does it mean when Coloumb's force is Conservative?

If a particle moves around an E-Field, and will return to its initial position, the summation of work done by the charge to oppose the E-Field as it moves, minus the work done by the E-Field to the particle when the particle moves along with the E-Field, is equal to zero

105

Formula for Work done by a particle from point A to B under the influence of an E-Field

W(AB) = ΔPE = Q(test) (VA - VB)

Q(test) - Charge of the moving particle
VA - Voltage @ Point A
VB - Voltage @ Point B

106

Formula for the Speed of a particle from point A to B under the influence of an E-Field

Shift solve for 'v':
ΔPE = ΔKE
W(AB) = 0.5mv^2

Q(test)x(V(AB)) = 0.5m(v)^2

Q(test) - Charge of the moving particle
V(AB) = (VA - VB)
VA - Voltage @ Point A
VB - Voltage @ Point B

107

The Locus of points around a charge where the Electric Field Intensity and Voltage is equal

Equipotential Lines

108

Equipotential lines are (Parallel/Perpendicular) to the Electric Field Lines

Perpendicular

109

The Electric Field is obtained by performing a ________ Operator on the __________

Gradient Operator on the Voltage
E(vector) = - ∇(Voltage)

Note: Gradient transforms a scalar field into a vector field

110

Formula for Capacitance between two parallel plates

C = (εo A) / d
"Seed"

A - Area of plates
d -Distance between plates

111

The electric field inside a conductor is ____

E = 0 V/m

112

Charges in a conductor will ______ on the outer surface of a conductor

Uniformly Distribute

113

Inside an enclosed surface made out of a conductor, there is no ________ or ________

Charge or Electric Field

114

Conductors throughout its material is said to be __________ in terms of voltage

Equipotential

115

An enclosed surface build for the purpose of electrostatic shielding

Faraday's Cage

116

What happens when you introduce a charge inside a Faraday's Cage?

Ex. if a positive charge is placed inside, the inner surface of the Faraday's Cage will be Negatively, but Equally Charged as that of the positive charge inside

but since conductors(The faraday cage) are equipotential (E = 0), the outer surface of the cage will be positively charged, as equally as the negatively charged inner surface

117

What Electric Field Intensity is Required for a High Voltage Breakdown(in air)?

3 x 10^6 V/m

118

A Famous example of A high Voltage Breakdown (An electric field of 3x10^6 V/m) is the weather phenomenon called _________

Lightning

119

When a High Voltage Breakdown paired with a continuous flow of current occurs, it causes the ________

Corona Effect / St. Elmo's Fire

120

A ______ Magnet is always a permanent magnet

Natural

121

An _______ Magnet requires the phenomenon of electromagnetism

Artificial

122

When the Relative Permeability of a material (μr) is Greater than or equal to 100, the material is said to be ________

Ferromagnetic

123

When the Relative Permeability of a material (μr) is Slightly greater than 1, the material is said to be ________

Paramagnetic

124

When the Relative Permeability of a material (μr) is Slightly less than 1, the material is said to be ________

Diamagnetic

125

The Most Famous Diamagnetic Material is ________

Copper

126

A Diamagnetic Material (Deflects/Attracts) Magnetic Flux Lines

Deflects

127

When the Relative Permeability of a material (μr) is equal to 1, the material is said to be ________

Non-Magnetic

128

1 Weber is equal to ________ Maxwells

1 Wb = 1 x 10^8 Mx

129

The CGS equivalent of Tesla (Wb/m^2)

GAUSS:

1 Gauss = 1 Mx/cm^2

130

THEORY: A coil of wire in the presence of a changing magnetic field will "induce" a voltage across the coil

FARADAY'S LAW

V = NdΦ/dt

N - number of turns
dΦ - change in Magnetic Flux Lines
dt - as time changes

131

Will a coil of wire in the presence of a static magnetic field induce a voltage?

no
(based on V = NdΦ/dt, no change in dΦ means no voltage)

132

Alternative Magnetic Flux Density Formula

B = μH

B - Magnetic Flux Density (Wb/m^2)
μ - Permeability (μ = μrμo) (in Henrys/m)
H - Magnetic Field Intensity (in Henrys or Ampere-turn/meter)

133

Unit for Permeability of Free Space

μo - 4π x 10^-7 H/m

Unit is in Henrys / meter (H/m)

134

Formula for alternative interpretation of Faraday's Law

V = L (di/dt)

V - voltage induced in a coil
L - Inductance of Coil (in Henrys)
di - Change in Current
dt - change in time

135

Will there be an induced voltage when the current through a coil is DC?

No
(based on V = L (di/dt), no change in di means no voltage)

136

Combining the two equations for Faraday's Law gives this equation:

V = NdΦ/dt And V = L (di/dt)

NdΦ/dt = L (di/dt)
∫NdΦ/dt = ∫L (di/dt)

Final Equation:

NΦ = Li

N - Number of Turns in a coil
Φ - Magnetic Flux lines
L - Inductance
i - Current

137

Combining:

NΦ = Li,
B = μH,
H = mmf/ l,
mmf = Ni
and B=Φ/A

will give the formula for __________

INDUCTANCE FORMULA:
B = μH --------EQ 1
B=Φ/A ---------EQ 2
NΦ = Li >>>>>>> Φ = Li/N ----EQ 3
H = mmf/ l --------EQ 4
mmf = Ni --------EQ 5

EQ1 + EQ2
Φ/A = μH >>>>>>>>> ADD EQ3 (substitute Φ)
Li/NA = μH >>>>>>>> ADD EQ4 (substitute H)
Li/NA = μ mmf/ l >>>>>>> ADD EQ5 (substitute mmf)
Li/NA = μ . Ni/ l

FINAL FORMULA:

L = μ(N²)A / l (in Henrys)
"LUNAL"

μ - Permeability
l - length of inductor coil
N - Number of Turns
A - Area

138

THEORY: a supplement to Faraday's Law, where it indicates that the polarity the induced EMF in the presence of a changing magnetic field

LENZ LAW:

V = -NdΦ/dt

139

The effect observed when electrons are pushed to one side of a conductor that carries current, due to the presence of a magnetic field, Polarizing the conductor, making one side positive, and another negative, that results to a voltage across the width of the conductor

Hall Effect

140

Formula for the Hall Voltage in the conductor due to the Hall Effect

V(hall) = I*B / [n(qe)d]

I - Current in conductor(Amperes)
B - Magnetic Flux Density (in Tesla)
qe - electron charge (-1.6 x 10^-19 Coloumbs)
d - Thickness of conductor (not Area)
n - Volumetric Electron Density (#e- / m^3)

141

Formula for Electron Density(n) of a material

n = ρ(NA) / MM

ρ - Density of Conductor
NA - Avogadro's Number (6.022 x 10^23 particles/mole)
MM - (Molar Mass (g/mol))

142

Electron Density(n) for copper

n(copper) =8.5 x 10^28 (in #e- / m^3)

143

Formula for Drift Velocity ¯\_(ツ)_/¯

Vd = I / [n(qe)A]

I - Current in conductor(Amperes)
qe - electron charge (-1.6 x 10^-19 Coloumbs)
A - Cross Sectional Area of conductor
n - Volumetric Electron Density (#e- / m^3)