Ohm’s law
I = V / R
Joule’s law
P = V · I = I 2 · R = V 2 / R
Series circuit rules
VT = V1 + V2 + V3 + …
IT = I1 = I2 = I3 = …
RT = R1 + R2 + R3 + …
1/CT = 1/C1 + 1/C2 + 1/C3 + …
LT = L1 + L2 + L3 + …
Parallel circuit rules
VT = V1 = V2 = V3 = …
IT = I1 + I2 + I3 + …
1/RT = 1/R1 + 1/R2 + 1/R3 + …
CT = C1 + C2 + C3 + …
1/LT = 1/L1 + 1/L2 + 1/L3 + …
Voltage division
V1 = VT ⋅ R1 / (R1+R2+R3+…)
Current division
I1 = IT ⋅ (R2+R3+…) / (R1+R2+R3+…)
Kirchhoff’s voltage law (KVL)
The sum of voltage drops at a current loop is zero:
∑ Vi = 0
Kirchhoff’s current law (KCL)
The junction between several circuit elements is called a node.
The sum of the currents values at a node is zero:
∑ Ii = 0
Capacitance
C = Q / V
Parallel plate capacitor
C = ε ⋅ A / l
ε is the permittivity in farad per meter (F/m).
Permittivity
ε = ε0 ⋅ εr
ε0 is the permittivity in the vacuum.
εr is the relative permittivity or dielectric constant.
Current of capacitor
IC(t) = C dVC(t) / dt
Voltage of capacitor
VC(t) = VC(0) + 1/C ∫ IC(t)⋅dt
Voltage of capacitor
VL(t) = L dIL(t) / dt
Current of inductor
IL(t) = IL(0) + 1/L ∫VL(t)⋅dt
Energy of capacitor
WC = C⋅V 2 / 2
Energy of inductor
WL = L⋅I 2 / 2