The resistance of a length L of conductor with cross sectional area A is defined as
where is the resistivity and is the electrical conductivity. The MKS unit of
resistance is the Ohm, denoted
Resistance is related to the voltage V and current I via Ohm's law,
Resistance is temperature-dependent, and to first order given by
where R is a reference resistance at a fixed temperature, is the temperature offset, and is the thermal resistance coefficient.
Resistors in parallel have an effective resistance given by
while resistors in series have an effective resistance of
Resistance can be generalized to sinusoidal current flow, wave propagation, etc. using the concept of impedance.
Impedance, Radiation Resistance, Resistivity, Resistor, Thermal Resistance Coefficient
