Current, Resistance & Potential Difference (OCR GCSE Physics A (Gateway Science Suite)): Revision Notes

In addition to current, we can also measure the potential difference (pd) and resistance in a circuit.

Potential difference is the driving force that causes electric charges to flow through a circuit. It is measured in volts (V) and can be measured using a voltmeter. A voltmeter must be connected in parallel with the component for which you want to determine the potential difference.

Resistance slows down the flow of electrical charges in a circuit. It is measured in ohms (Ω).

The current, potential difference and resistance are related by the equation:

Where:

• V is the potential difference in volts (V)
• I is the current in amps (A)
• R is the resistance in ohms (Ω)

There are various ways to alter the current and potential difference in a circuit. In this experiment, you will investigate how changing the length of a wire affects resistance.

Conducting the Experiment

1. Set up a circuit as shown in the circuit diagram.
2. Using a ruler, measure the distance between the two crocodile clips. This is the "wire length."
3. Close the switch and record the current on the ammeter and the potential difference on the voltmeter.
4. Adjust the crocodile clips to change the wire length. Repeat the measurements of length, current, and potential difference.
5. Repeat the experiment for several different wire lengths. Now, use your results to explore the relationship between resistance and wire length.

Rearrange the equation V=IRV = IRV=IR to find R=VIR = \frac{V}{I}R=IV​, and use this equation to calculate the resistance of the wire for each length.

Plot the resistance against the wire length on a graph. Draw a line of best fit, which should be a straight line passing through the origin. This line demonstrates that resistance is directly proportional to wire length.

You can also modify this experiment to investigate the effect of adding resistors in series and parallel.