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Electricity and Circuits

Resistors in series and in parallel

  • 2 things to know
  • Paper 6

Overview

Why series resistors add and parallel resistors reduce the total, two identical resistors in parallel, and calculations of current and potential difference in series circuits.

What you need to know

Answer each one before you reveal it.

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Key term

Why does adding a second resistor in series increase the total resistance of a circuit?

Key term

How is the total resistance of two resistors in series found?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why does adding a second resistor in series increase the total resistance of a circuit?

    Model answer

    The charge has to pass through both resistors one after the other, so the total opposition is the sum of the two.

  2. 2

    How is the total resistance of two resistors in series found?

    Model answer

    The two resistances are added together.

  3. 3

    Why does connecting a second resistor in parallel decrease the total resistance?

    Model answer

    The extra branch gives the charge another path, so a larger current flows from the supply for the same potential difference.

  4. 4

    Two 10 Ω resistors are connected in series. What is their combined resistance?

    Model answer

    The combined resistance is 10 Ω + 10 Ω = 20 Ω.

  5. 5

    How does the total resistance of two identical resistors in parallel compare with the resistance of one of them alone?

    Model answer

    The total resistance is half the resistance of one of the resistors.

  6. 6

    Why is the total resistance of a parallel combination always smaller than the smallest single resistance in it?

    Model answer

    Every extra branch adds another path for current, so the current from the supply is larger than the current through any one branch alone.

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