Circuits, Formulas and Tables Electrical Engineering  Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.) 
11. Basic symbols and formulas of electrical engineering 

Ohm’s Law 
_{}  
power 
P = U_{2} · I 
[W] 

P = I^{2} · R 
[W] 

_{} 
[W] 
work 
W = U · I · t 
[V · A · s = Ws] 

W = P · t 
[W · s = Ws] 
diameter of a conductor 
_{} 
[mm^{2}] 
resistance of a conductor 
_{} 
[W] 

_{} 
[W] 
influence of temperature on the resistance of the conductor 
R_{W} = R_{K} 
[1 + µ(J_{2}  J_{1})] 
Connection of resistances and power sources
· series connection
Figure
Figure
R_{G} = R_{1} + R_{2} + R_{3} (total resistance)
U = U_{1} + U_{2} + U_{3}.....
E_{G} = E_{1} + E_{2} + E_{3}
_{} 
condition: R_{i1} = R_{i2} = R_{i3} 
U = I · R_{a}
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
R_{E} = equivalent resistance  
I_{G} = total current intensity  
_{} 
Condition: 

Equal power sources are connected in parallel. 

E = E_{1} = E_{2} = E_{3} 
for 2 resistances connected 
_{} 
for n equal resistances 
_{} 

I_{G} = I_{1} + I_{2} + I_{3} 
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.
I_{G}  I_{1}  I_{2}  I_{3} = 0
Figure