Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Calculate the currents, potential differences and resistances in series…
Full specification wording
Topic 10 – Electricity and circuits: 10.15 Calculate the currents, potential differences and resistances in series circuits
In a series circuit the components form a single loop, so the same current flows through every component: I = I₁ = I₂ = I₃.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 15 of 39
Study notes
From the checked teaching notes for this specification point.
The idea
In a series circuit the components form a single loop, so the same current flows through every component: I = I₁ = I₂ = I₃. The supply potential difference is shared between the components, so the potential differences add: V = V₁ + V₂ + V₃. The total resistance is the sum of the individual resistances: R = R₁ + R₂ + R₃. Combine these with V = IR to find an unknown. For example, a 12 V supply drives 2 A through a 3 Ω resistor and a second resistor in series: the second resistor has V = 12 V − 6 V = 6 V and R = 6 V ÷ 2 A = 3 Ω. Check units: volts, amperes and ohms.
What earns the marks
- States that the current is the same at every point in a series circuit.
- Adds the potential differences across components to give the supply potential difference.
- Adds the individual resistances to give the total resistance of the series circuit.
- Applies V = IR to a single component to find an unknown current, potential difference or resistance.
- Uses the total resistance and supply potential difference together to find the circuit current.
Common mistakes and how to put them right
Adds the currents through series components.
Put it right: Keep the current the same throughout the loop.
Adds the potential differences to find the total resistance.
Put it right: Add resistances instead and use V = IR for potential differences.
Divides the supply potential difference equally between unequal resistors.
Put it right: Share it in proportion to resistance.
Uses the total resistance with a single component's potential difference.
Put it right: Pair total resistance with the supply potential difference.
Exam tips
- Write the series rules first (same current, add potential differences, add resistances), then substitute values.
- Show the V = IR substitution for each unknown so the working is visible.
- Check the answer by confirming the component potential differences add to the supply value.
- Keep units consistent and state them with the final answer.
Try the lesson
The start of the Topic 10 – Electricity and circuits: 10.15 Calculate the currents, potential differences and resistances in series circuits lesson, made from checked teaching notes for this specification point.
Have a go first
A series circuit contains a 3 V battery and two lamps. What is the total potential difference supplied to the two lamps?
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