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close this bookCircuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.)
close this folder11. Basic symbols and formulas of electrical engineering
View the document(introduction...)
View the document11.1. General direct current engineering
View the document11.2. Magnetic field
View the document11.3. Law of induction
View the document11.4. Electric field
View the document11.5. Alternating current engineering
View the document11.6. Calculation of power

11.1. General direct current engineering

Ohm’s Law


P = U2 · I


P = I2 · R




W = U · I · t

[V · A · s = Ws]

W = P · t

[W · s = Ws]

diameter of a conductor


resistance of a conductor



influence of temperature on the resistance of the conductor


[1 + µ(J2 - J1)]

Connection of resistances and power sources

· series connection



RG = R1 + R2 + R3 (total resistance)

U = U1 + U2 + U3.....

EG = E1 + E2 + E3

condition: Ri1 = Ri2 = Ri3

U = I · Ra

2. Kirchhoff’s Law

The sum of all voltages around a closed path in an electrical system is zero.

The sum of the impressed voltage is equal to the sum of the voltage drops.

· parallel connection



RE = equivalent resistance

IG = total current intensity


Equal power sources are connected in parallel.

E = E1 = E2 = E3

for 2 resistances connected

for n equal resistances

IG = I1 + I2 + I3

1. Kirchhoff’s Law

At each junction the sum of the currents flowing toward the junction is equal to the sum of the currents flowing away from the junction.

IG - I1 - I2 - I3 = 0