Grade: 10
Subject: Physical Sciences
Term: 2
CAPS Type: Informal Practical Investigation
Topic: Electric Circuits, Series Circuits, Parallel Circuits, Current, Potential Difference
Aim
To investigate how current and potential difference behave in series and parallel circuits.
Learning Outcome
- Build a series circuit.
- Build a parallel circuit.
- Compare current in series and parallel circuits.
- Compare potential difference in series and parallel circuits.
- Observe the effect of adding bulbs to a circuit.
- Explain the behaviour of current and potential difference in different circuit types.
Time Allocation
Approximately 60 minutes.
How Does It Work?
An electric circuit allows electric charge to flow when the circuit forms a complete closed path.
There are two common types of electric circuits: series circuits and parallel circuits.
Series Circuit
- Components are connected in a single path.
- Charge can only move through one route.
- The same current flows through every component.
- Potential difference is shared between the components.
Parallel Circuit
- Components are connected in separate branches.
- Charge can move through more than one route.
- Current splits between the branches.
- Each branch receives approximately the same potential difference as the battery.
Scientific Background
Current is the flow of electric charge through a conductor.
Potential difference is the electrical push supplied by the battery.
In a series circuit, current is the same throughout the circuit. Adding more bulbs increases the total resistance and the bulbs usually become dimmer.
In a parallel circuit, current splits between the branches. The total current is equal to the sum of the branch currents. Bulbs usually shine brighter than in series circuits, and one branch can continue working even if another branch fails.
Important measurement reminder:
An ammeter measures current and must be connected in series.
A voltmeter measures potential difference and must be connected in parallel across the component being measured.
Hypothesis
If bulbs are connected in series, then the current will be the same throughout the circuit and the bulbs will share the potential difference.
If bulbs are connected in parallel, then the current will split between the branches and each branch will receive approximately the same potential difference as the battery.
Variables
Independent Variable
Type of circuit, series or parallel.
Dependent Variables
- Current readings.
- Potential difference readings.
- Bulb brightness.
Control Variables
- Same battery or cells.
- Same bulbs.
- Same connecting leads.
- Same measuring instruments.
Apparatus
- Torch cells or battery pack
- 2 identical light bulbs
- Bulb holders
- Ammeter
- Voltmeter
- Switch
- Connecting leads
- Circuit board, optional
Safety Precautions
- Use low-voltage cells only.
- Do not short-circuit the battery.
- Open the switch before changing connections.
- Check meter connections carefully before switching on the circuit.
- Disconnect the circuit after the investigation.
- Handle bulbs carefully if they become warm.
Experiment Part A: Series Circuit
Aim
To investigate current and potential difference in a series circuit.
Method
- Connect two identical light bulbs in series with the battery and switch.
- Close the switch and observe the brightness of the bulbs.
- Connect the ammeter in series at one position in the circuit.
- Record the current reading.
- Move the ammeter to another position in the same circuit.
- Record the current reading again.
- Connect the voltmeter in parallel across bulb 1.
- Record the potential difference across bulb 1.
- Connect the voltmeter across bulb 2.
- Record the potential difference across bulb 2.
- Connect the voltmeter across the battery.
- Record the battery potential difference.
Results Table: Series Circuit Current
| Ammeter Position | Current Reading (A) |
|---|---|
| Position 1 | |
| Position 2 | |
| Position 3 |
Results Table: Series Circuit Potential Difference
| Component Measured | Potential Difference (V) |
|---|---|
| Bulb 1 | |
| Bulb 2 | |
| Battery |
What Learners Should Observe
- Both bulbs light up.
- The bulbs may appear dimmer than in a single-bulb circuit.
- Current readings are approximately the same throughout the circuit.
- Potential difference is shared between the bulbs.
- The total potential difference across the bulbs is approximately equal to the battery voltage.
Conclusion
In a series circuit, current remains the same throughout the circuit and potential difference is shared between the components.
Experiment Part B: Parallel Circuit
Aim
To investigate current and potential difference in a parallel circuit.
Method
- Connect two identical light bulbs in parallel with the battery and switch.
- Close the switch and observe the brightness of the bulbs.
- Connect the ammeter in the main circuit before the branches.
- Record the total current.
- Move the ammeter to branch 1.
- Record the current in branch 1.
- Move the ammeter to branch 2.
- Record the current in branch 2.
- Connect the voltmeter across bulb 1.
- Record the potential difference across bulb 1.
- Connect the voltmeter across bulb 2.
- Record the potential difference across bulb 2.
- Connect the voltmeter across the battery.
- Record the battery potential difference.
Results Table: Parallel Circuit Current
| Ammeter Position | Current Reading (A) |
|---|---|
| Main Circuit | |
| Branch 1 | |
| Branch 2 |
Results Table: Parallel Circuit Potential Difference
| Component Measured | Potential Difference (V) |
|---|---|
| Bulb 1 | |
| Bulb 2 | |
| Battery |
What Learners Should Observe
- Bulbs usually shine brighter than in the series circuit.
- Current splits between the branches.
- The total current is approximately equal to the sum of the branch currents.
- Each branch receives approximately the same potential difference as the battery.
- If one branch is disconnected, the other branch can still work.
Conclusion
In a parallel circuit, current splits between the branches and the potential difference across each branch is approximately equal to the battery potential difference.
Comparison Between Series and Parallel Circuits
| Feature | Series Circuit | Parallel Circuit |
|---|---|---|
| Number of paths | One path | More than one path |
| Current | Same throughout | Splits between branches |
| Potential difference | Shared between components | Same across each branch |
| Bulb brightness | Usually dimmer | Usually brighter |
| If one bulb fails | Whole circuit stops | Other branches continue working |
Important Note
Ammeter: must always be connected in series.
Voltmeter: must always be connected in parallel.
Incorrect meter connections may damage the instruments or produce incorrect readings.
Expected Results
Series Circuit
- Equal current throughout the circuit.
- Shared potential difference.
- Dimmer bulbs.
Parallel Circuit
- Current splits between branches.
- Equal potential difference across branches.
- Brighter bulbs.
Questions for Learners
- What is the difference between a series circuit and a parallel circuit?
- What happens to current in a series circuit?
- What happens to current in a parallel circuit?
- How is potential difference shared in a series circuit?
- What happens to potential difference in a parallel circuit?
- Why are bulbs usually brighter in parallel?
- What happens if one bulb fails in a series circuit?
- What happens if one bulb fails in a parallel circuit?
- Why must an ammeter be connected in series?
- Why must a voltmeter be connected in parallel?
Common Mistakes
- Connecting the ammeter incorrectly.
- Connecting the voltmeter incorrectly.
- Creating a short circuit.
- Leaving the switch closed while changing the circuit.
- Comparing bulbs that are not identical.
- Confusing current and potential difference.
- Measuring potential difference without connecting the voltmeter across the component.
Teacher Notes
- This experiment should focus on circuit behaviour rather than detailed meter training.
- Learners should already know how to connect ammeters and voltmeters correctly.
- Use identical bulbs for clearer comparisons.
- Weak batteries may affect brightness observations.
- Encourage learners to predict the behaviour of each circuit before taking measurements.
Teacher Tip
Demonstrate the effect of removing one bulb from both circuit types to reinforce the difference between series and parallel circuits.
Extension Activity
- Investigate three bulbs in series.
- Investigate three bulbs in parallel.
- Investigate the effect of adding extra branches.
- Investigate the effect of removing one bulb from the circuit.
Real-World Application
Parallel circuits are used in household wiring because appliances can work independently.
Series circuits are used in some simple devices, decorative lights and protection circuits.
Understanding circuit behaviour is important in electrical engineering, electronics, appliance design and electrical troubleshooting.