# 2.2.1 Series & Parallel Circuits

### Series & Parallel Circuits

Diagram showing two bulbs connected in series

• A parallel circuit consists of two or more components attached along separate branches of the circuit Diagram showing two bulbs connected in parallel

### Series Circuits

• In a series circuit:
• The current is the same at all points ie. through each component
• The total potential difference of the power supply is shared between the components
• The total resistance of two components is the sum of the resistance of each component Lamps connected in a series circuit

• In the above circuit:
• The current from the power supply is the same as the current in both lamps I = I1 = I2
• If the battery is marked 12 V, then the potential difference would be 12 ÷ 2 = 6 V across each lamp
• If each lamp has a resistance of R, then the total resistance in the circuit is equal to R + R = 2R

### Parallel Circuits

• In a parallel circuit:
• The total current through the whole circuit is the sum of the currents through the separate components
• The potential difference across each component is the same
• The total resistance of two resistors is less than the resistance of the smallest individual resistor Lamps connected in a parallel circuit

• In the above circuit:
• Because the current splits up, the sum of currents in each branch will equal the current from the power supply I = I1 + I2
• If the battery is marked 12 V, then the potential difference would be 12 V across each lamp
• If each lamp has a resistance of R, then the total resistance in the circuit will be less than 2R
• Note that the current does not always split equally – often there will be more current in some branches than in others
• The current in each branch will only be identical if the resistance of the components along each branch are identical
• Current behaves in this way because it is the flow of electrons:
• Electrons are physical matter – they cannot be created or destroyed
• This means the total number of electrons (and hence current) going around a circuit must remain the same
• When the electrons reach a junction, however, some of them will go one way and the rest will go the other Current is split at a junction into individual branches ### Author: Katie

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.
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