IGCSEPhysicsCambridge (CIE)Revision Notes4. Electricity & MagnetismElectric Circuits & Electrical SafetyEMF & Potential Difference in Circuits

EMF & Potential Difference in Circuits (Cambridge (CIE) IGCSE Physics): Revision Note

Exam code: 0625 & 0972

Lindsay Gilmour

Written by: Lindsay Gilmour

Reviewed by: Tim

Updated on

E.m.f. 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

Diagram of four series cells labelled 3 V, 4 V, 2 V and 6 V, with a note showing their total e.m.f. adds to 15 V.
The total e.m.f. of these cells is equal to the sum of their individual e.m.f.s

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

Circuit diagram with a battery, two lamps in series and four voltmeters. The voltmeter across the battery shows V1+V2, the voltmeter across one lamp shows V1 and the voltmeter across the other lamp shows V2. The voltmeter across both lamps shows V1+V2.
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. 

Circuit diagram showing a battery of emf E in series with two resistors X with resistance R₁ and Y with resistance R₂.

[2]

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 [1 mark]

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

Step 3: Substitute in the known quantities and calculate VY

16 = 10 + VY

  • Therefore, the potential difference across Y is 6 V [1 mark]

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

Circuit diagram with a 12 V battery and two lamps of resistance R connected in parallel. The circuit shows currents I₁ and I₂ in each branch, a potential difference of 12 V across each lamp and a total current I₁ + I₂ in the loop.
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

Expertise: Physics Content Creator

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.

Tim

Reviewer: Tim

Expertise: Content Creator

Timothy graduated with a first class degree in Mathematics and Physics from the University of Warwick. After working as a postgraduate researcher, Timothy has worked as a content creator for various online revision platforms, creating physics resources for a range of levels and exam boards.