Required practical - investigate the factors that affect resistance
Jonny Nelson explains resistance with a GCSE Physics practical experiment.
There are different ways to investigate the factors that affect The opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms.. In this practical activity, it is important to:
- record the length of the wire accurately
- measure and observe the The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. and Moving electric charges, eg electrons moving through a metal wire.
- use appropriate apparatus and methods to measure current and potential difference to work out the resistance
Aim of the experiment
To investigate how changing the length of the wire affects its resistance.
Method
- Connect the circuit as shown in the diagram above.
- Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
- Record the reading on the A device used to measure electric current. and on the A device used to measure potential difference or voltage..
- Move one of the crocodile clips closer until they are 90 cm apart.
- Record the new readings on the ammeter and the voltmeter.
- Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
- Use the results to calculate the resistance of each length of wire by using R = V/I, where R is resistance, V is The potential difference across a cell, electrical supply or electrical component. It is measured in volts (V). and I is current.
- Plot a graph of resistance against length for the resistance wire.
Results
Some example results may be:
| Length (cm) | Potential difference (V) | Current (A) | Resistance (Ω) |
| 100 | 1.20 | 0.16 | 7.5 |
| 90 | 1.18 | 0.17 | 6.8 |
| 80 | 1.00 | 0.17 | 5.9 |
| 70 | 0.96 | 0.18 | 5.3 |
| 60 | 0.93 | 0.21 | 4.4 |
| 50 | 0.89 | 0.25 | 3.6 |
| 40 | 0.84 | 0.27 | 3.1 |
| 30 | 0.75 | 0.31 | 2.4 |
| 20 | 0.63 | 0.44 | 1.4 |
| 10 | 0.41 | 0.63 | 0.7 |
| Length (cm) | 100 |
|---|---|
| Potential difference (V) | 1.20 |
| Current (A) | 0.16 |
| Resistance (Ω) | 7.5 |
| Length (cm) | 90 |
|---|---|
| Potential difference (V) | 1.18 |
| Current (A) | 0.17 |
| Resistance (Ω) | 6.8 |
| Length (cm) | 80 |
|---|---|
| Potential difference (V) | 1.00 |
| Current (A) | 0.17 |
| Resistance (Ω) | 5.9 |
| Length (cm) | 70 |
|---|---|
| Potential difference (V) | 0.96 |
| Current (A) | 0.18 |
| Resistance (Ω) | 5.3 |
| Length (cm) | 60 |
|---|---|
| Potential difference (V) | 0.93 |
| Current (A) | 0.21 |
| Resistance (Ω) | 4.4 |
| Length (cm) | 50 |
|---|---|
| Potential difference (V) | 0.89 |
| Current (A) | 0.25 |
| Resistance (Ω) | 3.6 |
| Length (cm) | 40 |
|---|---|
| Potential difference (V) | 0.84 |
| Current (A) | 0.27 |
| Resistance (Ω) | 3.1 |
| Length (cm) | 30 |
|---|---|
| Potential difference (V) | 0.75 |
| Current (A) | 0.31 |
| Resistance (Ω) | 2.4 |
| Length (cm) | 20 |
|---|---|
| Potential difference (V) | 0.63 |
| Current (A) | 0.44 |
| Resistance (Ω) | 1.4 |
| Length (cm) | 10 |
|---|---|
| Potential difference (V) | 0.41 |
| Current (A) | 0.63 |
| Resistance (Ω) | 0.7 |
Analysis
Evaluation
From the graph it can be seen that the longer the piece of wire, the higher the resistance. Resistance is directly proportional to length as the graph gives a straight line through the origin.
Hazards and control measures
| Hazards | Consequences | Control measures |
| Heating of the resistance wire | Burns to the skin | Do not touch the resistance wire whilst the circuit is connected. Allow the wire time to cool. |
| Hazards | Heating of the resistance wire |
|---|---|
| Consequences | Burns to the skin |
| Control measures | Do not touch the resistance wire whilst the circuit is connected. Allow the wire time to cool. |
