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 FormulaeSo 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;

1) Find all the meter readings

2) What is the total resistance of the bottom branch

3) 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)