# Resistance and V=IR

There’s a formula linking Potential Difference and Current

• Potential Difference=Current x Resistance

# You can investigate the factors affecting resistance:

• The resistance of a circuit can depend on a number of factors, like whether components are in series or parallel, or the length of wire used in the circuit. You can investigate the effect of wire length using the circuit:

• The Ammeter: Measures the current flowing through the test wire. The ammeter must always be placed in series with whatever you’re investigating

• The Voltmeter: Measures the potential difference across the test wire. The voltmeter must always be placed in parallel around whatever you’re investigating, NOT around the other bit of the circuit.

• There can be parallel or series circuits

# Measuring the length of wire per resistance:

• Attach a crocodile clip to the wire level with 0cm on the ruler

• Attach the second crocodile clip to the wire. Write down the length of the wire between the clips

• Close the switch, then record the current through the wire and the pd across it

• Open the switch then move the second crocodile clip. Close the switch again, then record the new length, current and pd

• Repeat this for a number of different lengths of the test wire

• Use your measurements of current and pd to calculate the resistance for each length of wire, using R=V/I

• Plot a graph of resistance against wire length and draw a line of best fit

• Your graph should be a straight line through the origin, meaning resistance is directly proportional to length-the longer the wire, the greater the resistance

• If your graph doesn’t go through the origin, it could be because the first clip isn’t attached exactly at 0cm, so all of your length readings are a bit out