Resistance and V=IR Flashcards
Formula linking PD and Current
PD (V) = Current ( A ) x Resistance ( ohms )
The ammeter and voltmeter
The Ammeter measures current flowing through test wire and must always be placed in series with whatever your investigating
Voltmeter measures PD across wire and must always be placed in parallel with whatever your investigating - not around any other bit of the circuit
Investigate Effect of wire length using circuit PRACTICAL
1) Attach a crocodile clip to wire level with 0cm on ruler
2) Attach second crocodile clip to wire e.g. 10cm along wire and write down length of wire between the clips
3) close switch and record current through wire and pd across it
4) open switch then move the 2 crocodile clip e.g. another 10cm along wire and close switch and record new pd and current and length
5) repeat this with number of different lengths of test wire
6) calculate resistance for each length of wire, r=v/i
7) draw graph of resistance against wire length and draw line of best fit
8) Graph should be straight line through origin meaning resistance is directly proportional to length , longer wire = longer resistance
9) if graph does not go through origin, it could be that first clip isn’t attached exactly at 0 cm so all length readings are a bit out = systematic error
