Electricity: Current, PD, Series & Parallel Circuits

• Electricity is covered in this revision sheet, including current, potential difference (PD), series vs parallel circuits, key equations, units, mains electricity key terms, and series & parallel circuit recap.

Current

• Current is the rate of flow of charge.
• I = Q / t
• Measured using an ammeter.
• The unit for current is the Ampere (A).

Potential Difference (PD)

• Potential difference is the energy transferred per unit of charge between two points in a circuit.
• V = E / Q
• Measured using a voltmeter.
• The unit is the Volt (V).

Series vs Parallel Circuits

Series Circuit:

• There is only one path for current to flow.
• If one component breaks, the entire circuit stops working.
• Current is the same throughout the circuit.
• Voltage is shared across all components.
• Applications include old Christmas tree lights and flashlights.

Parallel Circuit:

• There are multiple paths for current to flow.
• If one component fails, the rest of the circuit still works.
• Current splits across branches.
• Voltage is the same across each branch.
• Applications include room lighting and household appliances (sockets).

Key Differences Between Series and Parallel Circuits

• Pathways: Series has one path, parallel has multiple paths.
• Voltage: Series is shared between components, parallel is the same across each branch.
• Current: Series is the same throughout, parallel splits across branches.
• Failure effect: In series, all components stop working; in parallel, other components still work.
• Resistance: In series, resistance increases with more components; in parallel, resistance decreases with more components.

Key Equations

• I = Q / t
• V = E / Q
• Q = I × t
• E = P × t
• E = V × I × t
• E = Q × V

Units

• E = Energy (Joules, J)
• P = Power (Watts, W)
• V = Potential Difference (Volts, V)
• I = Current (Amperes, A)
• t = Time (Seconds, s)
• Q = Charge (Coulombs, C)

Mains Electricity Key Terms

• Insulation: Non-conductive material to prevent electric shock.
• Double insulation: Two layers of insulation for extra safety.
• Earth / Ground: Path for electric current to safely discharge.
• Earthed / Grounded: Connected to ground to carry fault current away.
• Earthing: Process of discharging excess current into the earth.
• Plug (3-pin): Standard UK plug with live, neutral, and earth wires.
• Fuse: Safety device that melts to break the circuit if current is too high.
• Circuit breaker: Automatically switches off power during overload or short circuit.
• RCCB: Detects current leakage and disconnects supply to prevent electric shock.
• AC (Alternating Current): Current reverses direction periodically.
• DC (Direct Current): Current flows in one direction only.

Series & Parallel Recap

• Series Circuits:
  • Current is the same throughout.
  • Potential difference (PD) is shared.
  • Resistance adds up.
• Parallel Circuits:
  • Current splits across branches.
  • Potential difference (PD) is the same across each branch.
  • Total resistance decreases as more components are added.