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Some useful info about electrical:
Ampere
The constant current which when flowing through two parallel wires 1 m apart would produce in vacua a force of 2 x 10 -7 N/m
A
Coulomb
The quantity of if electricity when a current of 1 ampere flows for 1 second
C
Volt
The electromotive force or potential difference when a constant current of 1 ampere produces a heat in resistance at the rate of 1 newton-meter (joule)/second
V
Ohm
Is the electrical resistance of a conductor in which a constant curent of 1 ampere flow under a constant voltage of 1 volt
ω
Henry
The inductance in which 1 volt is produced by a currrent changing at the rate of 1 ampere/second
H
Farad
The Capacitance in which 1 couomb is stored for a potential difference of 1 volt
F
Siemens
The unit of electrical conductance S = A / V
S
Joule
The unit of energy work and quantity of heat. the work done when the point of application of a force of 1 newton is displaced through a distance of 1 metre in the direction of the force
J
Watt
The unit of power = t Joule/second
W
Weber
The unit of magnetic flux. The magnetic flux linking a circuit of one turn produces in it an electromotive force of 1 volt as it is reduced to zero at a uniform rate in 1 second
Wb
Tesla
The unit of magnetic flux density. The tesla is equal to 1 weber per square metre of circuit area
T
Ohms law
E = Voltage (Volts)
I = Current (Amperes)
R = Resistance (Ohms)
W = Power (Watts)
E = I x R = Sqrt (W x R) = W / I
I = E / R = Sqrt( W / R) = W / E
R = E / I = W / I2 = E2 / W
W = E x I = E2 / R = I2 x R
General Form of Ohms law
R = ρ . L / A
L = Length (metres),
A = Area (metre2,
ρ = resistivity (ω /metre)
Additive Resistances
Resistors in Series
R_total = R1 + R2 + R3...
Voltage across Resistors in Series
V_total = V_R1+V_R2+V_R3..
Resistors in Parallel
R_total = 1/ (1/R1 + 1/R2 +1/R3...)
The Voltage across Resistors in Parallel is the Same= V
Alternating Current Supplies
Alternating Voltage
e = e_max. sin ω. t = e_max .sin(f.t)
e_max = maximum voltage,
t = time (seconds),
ω = angular velocity rads/sec,
f = frequency (cycles /sec)
The Average value of a sinusoidal alternating quantity is calculated at 0.637x maximum value
The Root Mean Square(RMS) value of a sinusoidal alternating quantity is calculated at 0.707 x maximum value.
The form factor of a wave is the RMS value / Average Value = (for a sinusoidal wave) 1.1
The Peak (Crest) Factor is the Peak Value / RMS value = 1.414
Kirchoffs Laws
Kirchoffs First law.
The total current flowing towards a junction is equal to the total current flowing away from that junction.# i.e the algebraic sum of the currents flowing towards a junction is zero
Kirchoffs Second Law
In a closed circuit the algebraic sum of the products of the current and the resistance of each part of the circuit is equal to the resultant e.m.f in the circuit.
Capacitors
Q = V x C therefore I = C dV/dt
Q = Charge (coulomb)
V = Potential Difference (Volts)
C = Capacitance (Farad)
I = V / Xc
Xc = Capacitive Reactance (ω )
Xc = 1 / (2 p f C )
f = frequency (Herz)
Capacitors in Parallel
C_total. V = Q_total = Q1+Q2+Q3...
C_total. V = V.C1+V.C2+V.C3...
C_total = C1+C2+C3...
Capacitors in Series
C_total = 1/ (1/C1+1/C2+1/C3...)
Inductances
V = L.dI/dt
L = Inductance (Henry)
I = V/ XL
XL = Inductive Reactance (ω )
XL =2 p f L
f = frequency (Herz)
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