Electrostatics and Electromagnetism Flashcards
It states that like charges repel each other and unlike charges attract each other.
1st Law of Electrostatics
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
2nd Law of electrostatics
What is the formula for the force of attraction between charges?
F = k • (Q1 • Q2) / d^2 (Newton)
where k= 1/(4πεoεr)
How much is the absolute permittivity (εo)?
8.854 x 10^-12 Farad per meter
What is the relative permittivity (εr) in free space?
1
What is the value of k in free space or air (SI Units)?
9 x 10^9
1 coulomb = _______ statcoulomb or electrostatic units (ESU)
3x10^9
1 Newton = ____ dynes
1x10^5
This is an electric potential resulting from the location of charged bodies in the vicinity
Electrostatic Potential
What is the formula for Electrostatic/Electric Potential?
V = Q / (4πεoεrd) ; volts
1 volt = ___ joule/coulomb
1
This is the work done in moving one electron (sometimes called an elementary charge) in a field with a potential difference of 1 volt.
Electron Volt (eV)
1 eV = ________ joule
1.6 x 10^19
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.
Potential difference
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.
Electric Field Strength/Intensity
What is the formula for Electric Field Intensity?
E = (k • Q2) / d^2
What will happen to an insulating medium with voltage more than breakdown voltage is applied?
It will get punctured.
This is defined as the total number of electric lines of force emanating from a charged body.
Electric Flux (Ψ)
This is represented by an electric flux.
Electric Field
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.
Electric Flux density
What is the formula for Electric Flux density?
D = εoεrE
= Ψ/(4πr^2)
Where Ψ is equal to the Q (charge)
It states that the total flux out of a closed surface is equal to the net charge within the surface.
Gauss’ Law
What is the formula for Gauss’ Law
Q = D x Area of the Surface
It is the measure of how well a capacitor can store electrical charges.
Capacitance
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.
Capacitor
It is the unit of capacitance. it is one coulomb of charge on the plate/s raising its potential difference by one volt.
Farad (F)
C = Q/V
What is the formula for the capacitance of parallel-plate capacitors.
C = (εo•εr•A) / d
where d is the thickness of dielectric medium and A is the area of each plate
Formula for the capacitance of n-plate capacitor
C = (n-1) • (εo•εr•A) / d
where d is the thickness of dielectric medium and A is the area of each plate
What is the formula for the capacitance of multi-plate capacitor with different dielectrics.
C = (εo•A) / [ (d1/εo1) + (d2/εo2) + … + (dn/εon) ]
A circuit has two capacitances connected in series. How do you compute for the total capacitance
1/Ct = 1/C1 + 1/C2
What is the formula for Capacitance?
C = Q/V
Two capacitors are connected in Parallel. How do you compute for the total capacitance?
Ct = C1 + C2
What is the formula for the total energy stored in a capacitor?
W = (CV^2)/2
= QV/2
= Q^2 / 2C
It is the reciprocal of capacitance.
Elastance
It states that whenever the flux linking a coil or current changes, an emf is induced in it.
First Law of Faraday’s Law of Electromagnetic Induction
It states that the magnitude of the induced emf is proportional to the rate of change of flux linkages.
Second Law of Faraday’s Law of Electromagnetic Induction.
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.
Self-Inductance
It is a two terminal device that consist of a coiled wire wound in common core or in free air.
Inductor / choke coil
Unit of inductance
Henry
What is the formula for the voltage in an inductor?
V = L (di/dt)
What is the total inductance for inductors connected in series?
Lt = L1 + L2 + … + Ln
What is the total inductance for inductors connected in parallel?
Lt = 1 / [ (1/L1) + (1/L2) + … + (1/Ln) ]
It is the condition of inducing an emf in a coil or conductor by magnetic flux lines generated in another coil or conductors.
Mutual Induction
It is the amount or degree of mutual induction that exists between two coils or windings.
Mutual Inductance
What is the formula for the Energy stored in an Inductor
W = 1/2 LI^2
It is the space surrounding the magnet, where the magnetic effect is experienced.
Magnetic Field
This is the lines of force produced by a magnet.
Magnetic flux (Φ) ; maxwell or weber
1 line of force = ___ maxwell
1
1 weber = ______ maxwells
1 x 10^8
This is the flux that does not follow the intended path in a magnetic circuit.
Leakage Flux
This is the number of magnetic lines per unit area
Magnetic flux density
What is the formula for Magnetic Flux Density (B)
B=Φ/Acosθ ;Tesla or Gauss
where θ is the angle between the normal to the surface and a magnetic field vector
1 Tesla = ______ Gauss
10,000
It is the ability of a material to conduct magnetic flux through it.
Permeability (μ)
What is the formula of Permeability?
μ = μo • μr
= B/H ; Henry per meter
where μo is the absolute permeability and μr is the relative permeability
What is the value of Absolute permeability (μo) or the permeability of vacuum air (reference medium)
4 x 10^-7 H/m
It is the ratio of permeability of a given material to the permeability of vacuum of air.
Relative Permeability (μr)
It is the force experienced by a unit north pole at that point. It is also called magnetizing force or magnetic potential gradient.
Magnetic Intensity (H)
What is the formula for Magnetic Intensity (H)?
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
This is the cgs unit of magnetic field strength. It is equal to gilbert per centimeter.
Oersted
For magnetic flux, we use the __________ rule.
Right Hand Rule
For the right hand rule, the thumb indicates the direction of ________.
Current
For the right hand rule, the curled fingers indicates the direction of __________.
Magnetic Flux density
What is the formula for the force on a conductor carrying a current in a magnetic field
F = BILsinθ
What is the formula for the Force between current carrying parallel conductors
F = (2x10^-7) • (I1•I2) / (L/D)
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.
Magnetomotive force
What is the formula for magnetomotive force?
mmf = NI (SI, Ampere-turns)
= 0.4πNI (cgs, Gilberts)
This is the property of a magnetic material to oppose the flux from penetrating the material.
Reluctance (S)
It is the reciprocal of permeability.
Permeance
What is the formula for Reluctance?
S = length / (μo • μr • A)
where A is the cross-section area of the conductor
What is the relationship between the flux, mmf and reluctance.
Φ = NI/S
What is the formula for Reluctance in series?
St = S1 + S2 + … + Sn
What is the formula for Reluctance in Parallel?
St = 1/ [ (1/S1) +(1/S2) + … + (1/Sn) ]
The heat due to hysteresis released per cycle per unit volume or iron is approximately computed using:?
Steinmetz Formula
What is the General Formula for Hysteresis loss?
Pb = η * Bmax^n * f * V
The formula for hysteresis loss per cycle per unit volume of iron is _________.
Wh = η * f * Bmax^1.6
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)
Dynamically Induced emf
What is the formula for Dynamically Induced emf
E = BLvsinθ
where v is the velocity of wire movement.
This is the emf induced in a wire by changing the magnetic flux linking with the coil.
Statically Induced emf
What is the formula for Statically Induced emf?
E=N * dθ/dt
where N is the number of turns
This is a kind of magnetic material that is least magnetic. It has a relative permeability equal to 1.
Non-magnetic
This is a kind of magnetic material with relative permeability lesser than 1.
Diamagnetic
What is an example of a diamagnetic material?
Copper
It is a magnetic material with relative permeability slightly greater than 1
Paramagnetic
Give an example of a paramagnetic material.
Aluminum
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
Ferromagnetic
It is a magnetic material that does not absorb the magnetic field but repel it.
Diamagnetic
It is the amount by which relative permeability differs from unity and it has no unit.
Susceptibilty (Xm)
What is the formula for Susceptibility?
Xm = μr - 1
1 A-t (Ampere-turn) = _____ Gilbert (Gb)
1.256
1 oersted = ___ Gb/cm
1
It is the dependence of the state of a system on its history.
Hysteresis
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.
Coercivity
This is the ability of a material to retain magnetization.
Retentivity
This is another word for residual magnetism.
Remanence
