IGCSEPhysicsCIERevision Notes4. Electricity & MagnetismElectric Circuits & Electrical SafetyEMF & Potential Difference in Circuits

EMF & Potential Difference in Circuits (CIE IGCSE Physics)

Revision Note

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Lindsay Gilmour

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Physics

EMF in series

  • When several cells are connected together in series, their combined e.m.f. is equal to the sum of their individual e.m.f.s

Total EMF, IGCSE & GCSE Physics revision notes

The total e.m.f. of these cells is equal to the sum of their individual e.m.f.s

 

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Potential difference in series circuits

Extended Tier Only

  • In a series circuit, the sum of potential differences across the components is equal to the total e.m.f. (electromotive force) of the power supply

Potential difference in a series circuit

Voltage in series, IGCSE & GCSE Physics revision notes

In a series circuit the components share the e.m.f. of the power supply

 

Worked example

In the circuit diagram below, the power source has an e.m.f., E, of 16 V. There is a potential difference of 10 V across component X. Calculate the potential difference across component Y. 

9-3-2b-h-resistors-x-and-y-in-series

Answer:

Step 1: Recall the rule for potential difference in series

  • The sum of potential differences across components in series is equal to the e.m.f. across the power source

Step 2: Write an equation to determine the potential difference across Y

E = VX + VY

  • Where:
    • E is the e.m.f. of the power source = 16 V
    • VX is the potential difference across X = 10 V
    • VY is the potential difference across Y
  • Recall that:
    • E = 16 V
    • VX = 10 V

Step 3: Substitute in the known quantities and calculate VY

16 = 10 + VY

  • Therefore, the potential difference across Y is 6 V

Potential difference in a parallel circuit

Extended Tier Only

  • The potential difference across each branch of a parallel circuit is the same as the e.m.f. of the power source

Potential difference in a parallel circuit

Parallel Circuit Example

The power source has an e.m.f .of 12 V and there is a potential difference of 12 V across each branch

  • It is important to notice that the potential difference in a parallel circuit is equal across each branch
    • In the example above, if one branch in the circuit contained multiple components, the 12 V would be split between the components on that branch

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    Lindsay Gilmour

    Author: Lindsay Gilmour

    Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.