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2.2.2Electricity

Voltage in Series and Parallel

5 min read 5 parts Lesson 6 of 18 1 quiz

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Section 1 of 5Voltage in Series

2.2.2 Voltage in Series and Parallel

In a series circuit the supply voltage is shared between the components.

Shared voltage
  • The total voltage of the supply equals the sum of the voltages across each component in series.
Larger share
  • A component with a greater resistance has a larger share of the supply voltage in series.
Equal resistors
  • Identical components in series each have the same share of the supply voltage.
Energy view
  • The energy given to each coulomb by the supply is shared out among the components in series.

Section 2 of 5Voltage in Parallel

Each branch of a parallel circuit is connected directly across the supply, so it receives the full voltage.

Same voltage
  • Each parallel branch has the same potential difference as the supply, because they connect to the same two points.
Independent branches
  • The voltage across one branch does not change when another branch is added or removed.
Supply value
  • A voltmeter across any branch of a parallel circuit reads the supply voltage.
Energy transfer
  • Each coulomb of charge transfers the same energy in every branch of the parallel circuit.

Section 3 of 5Solving a Series Problem

Finding the total resistance first gives the current, which then gives each voltage.

1
Add the resistances in series to find the total resistance.
2
Use I = V ÷ R with the supply voltage to find the current through the circuit.
3
Use V = I × R for each component to find its share of the supply voltage.
4
Check that the component voltages add up to the supply voltage.

Section 4 of 5Worked Example

Question

  • A 12 V supply is connected to a 4 Ω resistor and an 8 Ω resistor in series.
  • Calculate the voltage across each resistor.

  1. Total resistance = 4 Ω + 8 Ω = 12 Ω.
  2. Current I = V ÷ R = 12 V ÷ 12 Ω = 1 A.
  3. Voltage across 4 Ω: V = 1 A × 4 Ω = 4 V.
  4. Voltage across 8 Ω: V = 1 A × 8 Ω = 8 V, and 4 V + 8 V = 12 V.

Answer The 4 Ω resistor has 4 V across it and the 8 Ω resistor has 8 V across it.

Section 5 of 5Exam Checklist & Tips

2.2.2 – Key Points for the Exam

  • Potential difference The energy transferred per unit charge between two points, also called voltage.
  • Series circuit A circuit in which components are connected one after another along a single path.
  • Parallel circuit A circuit in which components are connected across the same two points.
  • Supply voltage The potential difference provided by the cell or power supply to the circuit.

Common Mistakes

  • Adding the voltages across parallel branches; each branch has the supply voltage, not a share of it.
  • Assuming components in series all have the same voltage; the voltage depends on their resistance.
  • Forgetting to check that the component voltages in series add up to the supply voltage.
  • Stating that the current is the same in parallel branches;
    • the voltage is the same, but the current may differ.
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