Resistance Physics – 12.1.5 Series and parallel resistor circuits Understand how the resistance of components add up in a circuit Summate resistor networks by applying the formulae in various situations

GCSE Background From GCSE physics we already know that; V = IR So simply in this circuit the resistance of the bulb is 12. This is a measure of how much the bulb resists the flow of electrons. We should also have some idea of these graphs which show a “characteristic” behaviour of different conductors when we graph at V & I

Circuit Rules For resistance calculations at AS you can use the premise of the following rules;

Series Resistance

Parallel

Generalised Formulae So all this leads us to a generalised formulae for any number of resistance. In Series resistance is simple but for Parallel resistances we must use the reciprocal. NB: when multiplying out the second formula make sure you treat all terms equally!

Test it out…. If all the bulbs are of equal resistance answer the following; Find all the meter readings What is the total resistance of the bottom branch If I swapped all three bulbs for one bulb what resistance should it be so that the current flow in the main branch is still 3A (i.e. combine all resistances using formulae)