Resistance and Ohm’s Law

– Resistance is the opposition to the flow of current. Resistance x Current = Voltage, or:


For resistors in parallel, the reciprocal of the total resistance is equal to the sum of the reciprocals of the individual resistances:

If two equal resistors are in parallel, the total resistance is half the original. Factors affecting resistance are: • Length • Cross-sectional area • Material

Electrical Power – Power is the rate of the change of energy. 1 Watt = 1 Joule changed per second. Power is calculated by dividing energy by time. This can be transposed to give: