A-Level · Physics · AQA · Mark scheme decoded
AQA A-Level Physics: Electric Current and Potential Difference — mark scheme explained
The short answer
In AQA A-Level Physics, understanding the concepts of electric current and potential difference is crucial for grasping how circuits work. This section covers the definitions of these quantities, their relationships, and how to apply them in practical scenarios.
The question
A charge of 5 coulombs flows through a wire in 10 seconds. Calculate the current. [Paraphrased for study — not reproduced from any exam paper.]
Mark scheme, decoded
What each mark is really for — in plain English — and the wording trap that loses it.
- S1
Identify the given values: Q = 5 C, t = 10 s.
- S2
Use the formula for electric current: I = Q / t.
- S3
Substitute the values into the formula: I = 5 C / 10 s.
- S4
Calculate the result: I = 0.5 A.
Model answer
Worked through, with each step tagged to the mark it earns.
- S1
Identify the given values: Q = 5 C, t = 10 s.
- S2
Use the formula for electric current: I = Q / t.
- S3
Substitute the values into the formula: I = 5 C / 10 s.
- S4
Calculate the result: I = 0.5 A.
Final answer: 0.5 A
Common mistakes
- Confusing current (I) with charge (Q). — Always double-check the units: I is in amperes (A), and Q is in coulombs (C).
- Using the wrong formula for potential difference. — Ensure you use the correct formula based on the given information: V = W / Q.
- Forgetting to convert units before calculations. — Always check and convert units to their standard forms (e.g., seconds for time, coulombs for charge) before performing calculations.
- Incorrectly connecting ammeters and voltmeters in circuits. — Remember that ammeters should be connected in series and voltmeters in parallel.
- Using the wrong formula for resistance. — Ensure you use the correct formula: R = V / I.
- Misinterpreting Ohm's law in practical scenarios. — Understand that Ohm's law (V = IR) applies to ohmic conductors under constant temperature conditions.
Where the marks go
- Full worked solution (all marking points)3 marks