  Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut f³r Berufliche Entwicklung, 201 p.)  11. Basic symbols and formulas of electrical engineering  (introduction...) 11.1. General direct current engineering 11.2. Magnetic field 11.3. Law of induction 11.4. Electric field 11.5. Alternating current engineering 11.6. Calculation of power

### 11.1. General direct current engineering

 Ohm’s Law power P = U2 · I [W] P = I2 · R [W] [W] work W = U · I · t [V · A · s = Ws] W = P · t [W · s = Ws] diameter of a conductor [mm2] resistance of a conductor [W] [W] influence of temperature on the resistance of the conductor RW = RK [1 + µ(J2 - J1)]

Connection of resistances and power sources

· series connection Figure Figure

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 Figure Figure

 RE = equivalent resistance IG = total current intensity Condition: 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 Figure