Continuous (direct) current

Electromotive force
Ε = A / q

Electromotive force - potential difference
Ε = φ1 - φ2

Current intensity (strength)
I = Δ_q / Δ_t

Current intensity (strength)
I = e n v S

Electric current density
j = I / S

Electric current density
j = e n v

Resistance
R = ρ l / S

Electrical conduction
λ = 1 / R

Resistance and temperature
R = R0(1 + α t)

Specific resistance
ρ = ρ0(1 + α t)

Specific conduction
σ = 1 / ρ

Connection in series: current intensity
I1 = I2

Connection in series: voltage
U = U1 + U2

Connection in series: resistance
R = R1 + R2

Parallel connection: current intensity
I = I1 + I2

Parallel connection: voltage
U1 = U2

Parallel connection: current intensity and resistance
I1 / I2 = R2 / R1

Parallel connection: current resistance
1/R = 1/R1 + 1/R2

Parallel connection: current resistance
R = R1 * R2 / (R1+R2)

Ohm's law
I = U / R

Ohm's law for closed circuit
Ε = I*R + Ir

Ohm's law for closed circuit: many current sources
nΕ = I*R + Inr

Work of electric current
A = Δ_q * U

Work of electric current
A = I*R^2 *t

Work of electric current
A = U^2 * t / R

Power of electric current
P = U * I

Power of electric current
P = I^2 * R

Power of electric current
P = U^2 / R

Work and power of electric current
A = P t