Resistors in Series (CIE A Level Physics)

Revision Note

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Expertise

Physics

In a series circuit, the combined resistance of two or more resistors is the sum of the individual resistances
In a series circuit:
- The current is the same through all resistors
- The potential difference is split between all the resistors
The equation for combined resistors in series is derived using Kirchhoff’s laws:

Derivation for resistors in series, downloadable AS & A Level Physics revision notes

The combined resistance of the components is equal to the sum of the individual resistances

Resistors in series diagram, downloadable AS & A Level Physics revision notes

Resistors connected in series each have their own separate voltage

$R = R_{1} + R_{2} + . . .$

The combined resistance R in the following series circuit is 60 Ω.

What is the resistance value of R₂?A. 100 Ω B. 30 Ω C. 20 Ω D. 40 Ω

Answer: C

Step 1: State the equation for the combined resistance for resistors in series

$R = R_{1} + R_{2} + . . . = R_{1} + R_{2} + R_{3}$

Step 2: Rearrange for resistance R₂

$R_{2} = R - (R_{1} + R_{3})$

Step 3: Substitute the values

$R_{2} = 60 - (30 + 10) = 20 Ω$

to absolutely everything:

the (exam) results speak for themselves:

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