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Comparing Series & Parallel Circuits (AQA GCSE Physics: Combined Science)
Revision Note
Comparing Series & Parallel Circuits
Current in Series & Parallel
- In a series circuit, the current is the same at all points
- In a parallel circuit, the current splits at junctions – some of it going one way and the rest going the other
Diagram showing the behaviour of current in series and parallel circuits
Potential Difference in Series & Parallel
- In a series circuit, the voltage of the power supply is shared between the components
- In a parallel circuit, the voltage across each component is the same
Diagram showing the behaviour of voltage in series and parallel circuits
Resistors in Series & Parallel
- In a series circuit, the total resistance is the sum of the resistance in each component
- Two resistors in series will have a larger overall resistance than just one
- This is because the charge has to push through multiple components when flowing around the circuit
- The more components the charge has to travel through, the higher the number of collisions that occur
- In a parallel circuit, the total resistance decreases and is less than the resistance of any of the individual components
- Two resistors in parallel will have a smaller overall resistance than just one
- This is because the charge has more than one pathway to take, so only some charge will flow along each path
- The more pathways there are, the smaller the amount of charge in each path
Series and Parallel Circuit Summary Table
Worked example
A circuit was set up as shown in the diagram.Calculate the resistance of the bulb.
Step 1: Determine the voltage across the bulb
- The components share the potential difference of the power supply, so:
12 V – 8 V = 4 V
Step 2: Write down the equation for voltage, current and resistance
V = IR
Step 3: Calculate the current through the resistor
I = V / R = 8 / 6 = 1.33 A
Step 4: Calculate the resistance of the bulb
- In a series circuit, the current is the same everywhere, so:
R = V / I = 4 / 1.33 = 3.0 Ω
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