Resistance Resistance is the measurement that describes the difficulty of flow of electric current. The relationship between the voltage, current and resistance is given by the following formula:                                                     Voltage = Current x Resistance  Resistance is measured in Ohms: Ω.. The greater the resistance, the more voltage is needed to push a current through the circuit.       Resistance in series circuit The total resistance R = R1 + R2     How changing the resistance in a series circuit changes the current for a given voltage For a given voltage, changing the resistance in a series circuit changes the current. For a given voltage, increasing the resistance in a series circuit decreases the current. For a given voltage, decreasing the resistance in a series circuit increases the current.     How changing the resistance in a parallel circuit changes the current for a given voltage       (Higher tier only)                           The total resistance of a parallel circuit is smaller than any resistance of the resistors. For a given voltage, changing the resistance in a parallel circuit changes the current. For a given voltage, as the resistance of the parallel circuit is smaller, the current increases.