EMF & Potential Difference in Circuits (Cambridge (CIE) IGCSE Physics)
Revision Note
Written by: Lindsay Gilmour
Reviewed by: Caroline Carroll
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
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
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.
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
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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