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EE > Electrostatics and Electromagnetism > Flashcards

Electrostatics and Electromagnetism Flashcards

1
Q

It states that like charges repel each other and unlike charges attract each other.

A

1st Law of Electrostatics

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2
Q

This states that the force of attraction or repulsion between charges is directly proportional to the product of two charges and inversely proportional to the square of the distance between them

A

2nd Law of electrostatics

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3
Q

What is the formula for the force of attraction between charges?

A

F = k • (Q1 • Q2) / d^2 (Newton)

where k= 1/(4πεoεr)

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4
Q

How much is the absolute permittivity (εo)?

A

8.854 x 10^-12 Farad per meter

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5
Q

What is the relative permittivity (εr) in free space?

A

1

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6
Q

What is the value of k in free space or air (SI Units)?

A

9 x 10^9

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7
Q

1 coulomb = _______ statcoulomb or electrostatic units (ESU)

A

3x10^9

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8
Q

1 Newton = ____ dynes

A

1x10^5

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9
Q

This is an electric potential resulting from the location of charged bodies in the vicinity

A

Electrostatic Potential

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10
Q

What is the formula for Electrostatic/Electric Potential?

A

V = Q / (4πεoεrd) ; volts

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11
Q

1 volt = ___ joule/coulomb

A

1

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12
Q

This is the work done in moving one electron (sometimes called an elementary charge) in a field with a potential difference of 1 volt.

A

Electron Volt (eV)

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13
Q

1 eV = ________ joule

A

1.6 x 10^19

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14
Q

The _________ between two points in an electric field is the amount of work needed to take a charge of 1C from one of the points to the other.

A

Potential difference

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15
Q

The ______________at any point within an electric field is given the force experienced by a positive charge of one coulomb placed at that point and is a vector quantity.

A

Electric Field Strength/Intensity

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16
Q

What is the formula for Electric Field Intensity?

A

E = (k • Q2) / d^2

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17
Q

What will happen to an insulating medium with voltage more than breakdown voltage is applied?

A

It will get punctured.

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18
Q

This is defined as the total number of electric lines of force emanating from a charged body.

A

Electric Flux (Ψ)

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19
Q

This is represented by an electric flux.

A

Electric Field

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20
Q

This is defined as the amount of flux passes through unit surface area in the space imagined at right angle to the direction of electric field.

A

Electric Flux density

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21
Q

What is the formula for Electric Flux density?

A

D = εoεrE
= Ψ/(4πr^2)

Where Ψ is equal to the Q (charge)

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22
Q

It states that the total flux out of a closed surface is equal to the net charge within the surface.

A

Gauss’ Law

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23
Q

What is the formula for Gauss’ Law

A

Q = D x Area of the Surface

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24
Q

It is the measure of how well a capacitor can store electrical charges.

A

Capacitance

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25
Q

This is any device on which electric charges can be stored so as to possess electric potential. It consists of two conducting plates separated by a layer of an insulating medium called dielectric.

A

Capacitor

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26
Q

It is the unit of capacitance. it is one coulomb of charge on the plate/s raising its potential difference by one volt.

A

Farad (F)

C = Q/V

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27
Q

What is the formula for the capacitance of parallel-plate capacitors.

A

C = (εo•εr•A) / d

where d is the thickness of dielectric medium and A is the area of each plate

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28
Q

Formula for the capacitance of n-plate capacitor

A

C = (n-1) • (εo•εr•A) / d

where d is the thickness of dielectric medium and A is the area of each plate

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29
Q

What is the formula for the capacitance of multi-plate capacitor with different dielectrics.

A

C = (εo•A) / [ (d1/εo1) + (d2/εo2) + … + (dn/εon) ]

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30
Q

A circuit has two capacitances connected in series. How do you compute for the total capacitance

A

1/Ct = 1/C1 + 1/C2

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31
Q

What is the formula for Capacitance?

A

C = Q/V

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32
Q

Two capacitors are connected in Parallel. How do you compute for the total capacitance?

A

Ct = C1 + C2

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33
Q

What is the formula for the total energy stored in a capacitor?

A

W = (CV^2)/2
= QV/2
= Q^2 / 2C

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34
Q

It is the reciprocal of capacitance.

A

Elastance

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35
Q

It states that whenever the flux linking a coil or current changes, an emf is induced in it.

A

First Law of Faraday’s Law of Electromagnetic Induction

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36
Q

It states that the magnitude of the induced emf is proportional to the rate of change of flux linkages.

A

Second Law of Faraday’s Law of Electromagnetic Induction.

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37
Q

This is defined as the phenomenon in which a change in electric current in a circuit produces an induced electro-motive force in the same circuit.

A

Self-Inductance

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38
Q

It is a two terminal device that consist of a coiled wire wound in common core or in free air.

A

Inductor / choke coil

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39
Q

Unit of inductance

A

Henry

40
Q

What is the formula for the voltage in an inductor?

A

V = L (di/dt)

41
Q

What is the total inductance for inductors connected in series?

A

Lt = L1 + L2 + … + Ln

42
Q

What is the total inductance for inductors connected in parallel?

A

Lt = 1 / [ (1/L1) + (1/L2) + … + (1/Ln) ]

43
Q

It is the condition of inducing an emf in a coil or conductor by magnetic flux lines generated in another coil or conductors.

A

Mutual Induction

44
Q

It is the amount or degree of mutual induction that exists between two coils or windings.

A

Mutual Inductance

45
Q

What is the formula for the Energy stored in an Inductor

A

W = 1/2 LI^2

46
Q

It is the space surrounding the magnet, where the magnetic effect is experienced.

A

Magnetic Field

47
Q

This is the lines of force produced by a magnet.

A

Magnetic flux (Φ) ; maxwell or weber

48
Q

1 line of force = ___ maxwell

A

1

49
Q

1 weber = ______ maxwells

A

1 x 10^8

50
Q

This is the flux that does not follow the intended path in a magnetic circuit.

A

Leakage Flux

51
Q

This is the number of magnetic lines per unit area

A

Magnetic flux density

52
Q

What is the formula for Magnetic Flux Density (B)

A

B=Φ/Acosθ ;Tesla or Gauss

where θ is the angle between the normal to the surface and a magnetic field vector

53
Q

1 Tesla = ______ Gauss

A

10,000

54
Q

It is the ability of a material to conduct magnetic flux through it.

A

Permeability (μ)

55
Q

What is the formula of Permeability?

A

μ = μo • μr
= B/H ; Henry per meter

where μo is the absolute permeability and μr is the relative permeability

56
Q

What is the value of Absolute permeability (μo) or the permeability of vacuum air (reference medium)

A

4 x 10^-7 H/m

57
Q

It is the ratio of permeability of a given material to the permeability of vacuum of air.

A

Relative Permeability (μr)

58
Q

It is the force experienced by a unit north pole at that point. It is also called magnetizing force or magnetic potential gradient.

A

Magnetic Intensity (H)

59
Q

What is the formula for Magnetic Intensity (H)?

A

H = Force / Magnetic Pole Strength = Newton/Weber
= (Number of Turns • Ampere) / mean length of flux lines (meter)
= Magnetomotive Force (Ampere-turn) / mean length of flux lines

60
Q

This is the cgs unit of magnetic field strength. It is equal to gilbert per centimeter.

A

Oersted

61
Q

For magnetic flux, we use the __________ rule.

A

Right Hand Rule

62
Q

For the right hand rule, the thumb indicates the direction of ________.

A

Current

63
Q

For the right hand rule, the curled fingers indicates the direction of __________.

A

Magnetic Flux density

64
Q

What is the formula for the force on a conductor carrying a current in a magnetic field

A

F = BILsinθ

65
Q

What is the formula for the Force between current carrying parallel conductors

A

F = (2x10^-7) • (I1•I2) / (L/D)

66
Q

This is the driving force required to drive the magnetic field through a magnetic circuit by passing an electric current (I) through a number of turns.

A

Magnetomotive force

67
Q

What is the formula for magnetomotive force?

A

mmf = NI (SI, Ampere-turns)

= 0.4πNI (cgs, Gilberts)

68
Q

This is the property of a magnetic material to oppose the flux from penetrating the material.

A

Reluctance (S)

69
Q

It is the reciprocal of permeability.

A

Permeance

70
Q

What is the formula for Reluctance?

A

S = length / (μo • μr • A)

where A is the cross-section area of the conductor

71
Q

What is the relationship between the flux, mmf and reluctance.

A

Φ = NI/S

72
Q

What is the formula for Reluctance in series?

A

St = S1 + S2 + … + Sn

73
Q

What is the formula for Reluctance in Parallel?

A

St = 1/ [ (1/S1) +(1/S2) + … + (1/Sn) ]

74
Q

The heat due to hysteresis released per cycle per unit volume or iron is approximately computed using:?

A

Steinmetz Formula

75
Q

What is the General Formula for Hysteresis loss?

A

Pb = η * Bmax^n * f * V

76
Q

The formula for hysteresis loss per cycle per unit volume of iron is _________.

A

Wh = η * f * Bmax^1.6

77
Q

This is the emf induced in a wire by moving either the wire or the magnet so that flux cutting results (principle used in generator)

A

Dynamically Induced emf

78
Q

What is the formula for Dynamically Induced emf

A

E = BLvsinθ

where v is the velocity of wire movement.

79
Q

This is the emf induced in a wire by changing the magnetic flux linking with the coil.

A

Statically Induced emf

80
Q

What is the formula for Statically Induced emf?

A

E=N * dθ/dt

where N is the number of turns

81
Q

This is a kind of magnetic material that is least magnetic. It has a relative permeability equal to 1.

A

Non-magnetic

82
Q

This is a kind of magnetic material with relative permeability lesser than 1.

A

Diamagnetic

83
Q

What is an example of a diamagnetic material?

A

Copper

84
Q

It is a magnetic material with relative permeability slightly greater than 1

A

Paramagnetic

85
Q

Give an example of a paramagnetic material.

A

Aluminum

86
Q

It is the most magnetic of all magnetic materials, It can retain magnetism and is used to create magnets. It has relative permeability highly greater than 1

A

Ferromagnetic

87
Q

It is a magnetic material that does not absorb the magnetic field but repel it.

A

Diamagnetic

88
Q

It is the amount by which relative permeability differs from unity and it has no unit.

A

Susceptibilty (Xm)

89
Q

What is the formula for Susceptibility?

A

Xm = μr - 1

90
Q

1 A-t (Ampere-turn) = _____ Gilbert (Gb)

A

1.256

91
Q

1 oersted = ___ Gb/cm

A

1

92
Q

It is the dependence of the state of a system on its history.

A

Hysteresis

93
Q

A magnetic moment at which the resistance of a magnetic material changes in magnetization. It is equivalent to field intensity necessary to demagnetize a fully magnetized material.

A

Coercivity

94
Q

This is the ability of a material to retain magnetization.

A

Retentivity

95
Q

This is another word for residual magnetism.

A

Remanence

EE (3 decks)

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