Charge, Current, Potential Difference and Resistance
Connecting charge flow, electrical energy transfer, current, potential difference, resistance, resistivity and current-voltage characteristics.
How to study A-level Physics
Define the system, represent the physics, select a justified model, calculate transparently, then test the result against units, limits and evidence.
Core concepts
Concept 1
Current is charge flow per unit time; potential difference is energy transferred per unit charge.
Exam cue: State the charge carriers and their conventional-current direction when relevant.
Concept 2
Resistance describes the ratio of potential difference to current under stated conditions and may vary with temperature or operating state.
Exam cue: Interpret the shape and gradient of an I-V or V-I graph carefully.
Concept 3
Resistivity is a material property related to resistance through conductor length and cross-sectional area.
Exam cue: Hold material and temperature assumptions explicit in resistivity calculations.
Risk pitfalls and guardrails
Calling current the amount of charge rather than its rate of flow.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Assuming every component obeys Ohm's law.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Using diameter instead of cross-sectional area in a resistivity calculation.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Memory anchors
Current
Current is charge transferred per unit time.
Potential Difference
Potential difference is energy transferred per unit charge.
Resistance
Resistance is potential difference divided by current at the stated operating point.
Ohmic Conductor
An ohmic conductor has current proportional to potential difference at constant physical conditions.
Resistivity
Resistance equals resistivity times length divided by cross-sectional area.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A current of 2.5 A flows for 40 s. How much charge passes?
A charge of 18 C passes a point in 6.0 s. What is the current?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”