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     $$\displaystyle G=\frac{I}{U}$$