# Resistors and Resistance

**Resistors in Series **

For resistors in series the total resistance can be calculated using the
following equation:

R = R1 + R2

Each series resistors has the same value for the current and the potential difference across each resistor add up to give the total voltage.

**Resistors in Parallel**

For resistors in parallel the total resistance can be calculated using
the following equation.

For each resistors in parallel the potential difference between them is
the same, however the currents add up to give the total current in the
circuit.

**Resistivity**

Unlike resistance, resistivity is a set value, which does not change regardless
of the area or length of a material and is therefore particularly useful
in engineering.

**Definition**

Numerically equal to the resistance of a one meter length of material
with a cross-sectional area of 1m^{2}.

**Equation**

Where

= Resistivity (m)

R = Resistance ()

V = Potential Difference (V)

L = Length (m)