ASPhysicsCambridge (CIE)Revision Notes10. D.C. CircuitsKirchhoff’s LawsResistors in Series

Resistors in Series (Cambridge (CIE) AS Physics): Revision Note

Exam code: 9702

Katie M

Written by: Katie M

Reviewed by: Caroline Carroll

Updated on

Deriving the equation for resistors in series

  • 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 shared 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

Resistors in series

  • When two or more components are connected in series:

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

Resistors in series

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

Resistors connected in series each have their own separate potential difference

 

  • The equation for the combined resistance, R  of resistors in series is:

R = R1 + R2 + ...

Worked Example

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 = R1 + R2 + ... = R1 + R2 + R3

Step 2: Rearrange for resistance R2

R2 = R − (R1 + R3)

Step 3: Substitute the values

R2 = 60 − (30 + 10) = 20 Ω

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Katie M

Author: Katie M

Expertise: Curriculum Expert

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

Caroline Carroll

Reviewer: Caroline Carroll

Expertise: Head of Content Delivery

Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about delivering high-quality resources to help students achieve their full potential.