Resistance and Conductance

Description how to calculate resistance and conductance

Resistance and Conductance

An electrical load provides resistance to the current in a circuit. The term resistance defines a conductor characteristic of the load in relation to the current. The current in a circuit is therefore dependent on the voltage and the resistance of the circuit.

Definition of resistance

The resistance of a load is greater, when the current is lower at the given voltage. Or the resistance of a load is greater, when a higher of voltage is required to reach a given current. The symbol of the resistance is \(R\).

The dependency can be defined as

\(\displaystyle Widerstand=\frac{Spannung}{Strom}\)         \(\displaystyle R=\frac{U}{I}\)
\(R\) = Widerstand
\(U\) = Spannung
\(I\) = Strom

The unit of measurement of the resistance is ohms (abbreviation \(Ω\). By definition, the resistance \(R = 1 Ω\) when the voltage \(U = 1Volt\) and the current is \(I= 1Amper\).

\(\displaystyle 1Ω=\frac{1V}{1A}\)

Definition of the Conductance

The greater the resistance of a load, the lower its ability to conduct electricity. This ability is the conductivity (symbol \(G\)). The unit of measurement of the conductivity is the Siemens (abbreviation \(S\)).

The conductance is thus the reciprocal of the resistance.

\(\displaystyle Leitwert=\frac{1}{Widerstand}\)         \(\displaystyle G=\frac{1}{R}\)     oder     \(\displaystyle R=\frac{1}{G}\)
Instead of     \(\displaystyle R=\frac{U}{I}\)     we can write    \(\displaystyle \frac{1}{G}=\frac{U}{I}\)

When the formula is changed, the definition for the conductance is given     \(\displaystyle G=\frac{I}{U}\)