**Resistance**is the capability of materials to impede the flow of current, or the flow of electric charge.- The circuit element used to model the resistance is called the resistor, R, and the unit is in
**Ohms (Ω)**. - Resistance of wires is assumed to be
**zero**.

Ohm’s law states that the voltage across a conductor is proportional to the current through the conductor. With passive sign convention, Ohm’s Law has two forms.

## Conductance

If the current is written as the function of voltage, we have:

where G is called **conductance** with a unit of **Siemens (s)**. It reflects the ability that an object conducts electricity.

No matter what the references are assigned, the power associated with resistors is always positive, which means resistors are the elements that always absorb energy in circuits.

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