O-Level and SEC G3 Physics K323
P14: Current of Electricity
Relate charge flow, current, potential difference, resistance, and current-voltage behaviour.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Current electricity links charge flow, energy per charge, resistance, wire dimensions, temperature and current-voltage characteristics. Conventional current and electron flow have opposite directions in metals.
Current, e.m.f. and potential difference
Current is charge flow rate. Conventional current is defined in the direction positive charge would move, opposite to electron drift in a metal. Charge is conserved around a complete circuit.
E.m.f. is work done per unit charge by a source around the complete circuit. Potential difference is work done per unit charge through a component. Both are measured in volts, but their roles in energy transfer differ.
Resistance and wires
Resistance is potential difference divided by current at a stated operating condition. For the same material and temperature, resistance is proportional to wire length and inversely proportional to cross-sectional area.
Heating a metallic conductor increases lattice vibration, making electron flow more strongly opposed, so resistance increases. Do not assume resistance stays constant for every component.
Current-voltage characteristics
An ohmic conductor at constant temperature has a straight line through the origin on an - graph. A filament lamp heats as current rises, so resistance increases and the graph becomes less steep.
A diode conducts strongly in one direction after its forward threshold region and has very small reverse current in the school model. Always check which variable is on each axis before interpreting gradient.
Formulae and relationships
| Relationship | Use |
|---|---|
| Relate charge, current and time. | |
| Relate potential difference or e.m.f. to energy per charge. | |
| Find resistance at an operating point. | |
| Compare wires of the same material and temperature. |
Worked examples
Example 1: A current of flows for . Find the charge transferred.
- Convert time: .
- Use .
- Report charge in coulombs.
Answer: (72 C).
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Define current as charge flow and potential difference as energy transferred per charge.
- Use resistance and current-voltage behaviour to distinguish conductors and components.
- Connect series sources to total e.m.f. while preserving polarity.
Official outcome coverage
K323 P14: 11 mapped outcomes, references P14(a), P14(b), P14(c), P14(d), P14(e), P14(f), P14(g), P14(h), P14(i), P14(j), P14(k). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Collect current-voltage pairs with correctly placed meters, change one variable systematically, and plot the appropriate characteristic.
Exam traps and retrieval check
Avoid these traps
- Using minutes without converting to seconds in .
- Treating e.m.f. and potential difference as identical descriptions.
- Taking - gradient as resistance when current is on the vertical axis.
Check from memory
Which way do electrons move in a metal?
Opposite to conventional current.
What happens to metallic resistance when temperature rises?
It increases.
Why is a filament-lamp - graph curved?
The filament heats and its resistance changes.
Pure versus Combined scope
Combined Physics revisits part of this core under CP12 Electric Charges and Current of Electricity, but with reduced outcome scope. Combined students should follow the component checklist rather than assume every K323 outcome is assessable.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.