AQA AS Level Physics Paper 2, June 2024: Question 6
1 mark · Medium difficulty · Multiple Choice
Calculate the number of electrons passing a point in a circuit in 7.0 minutes given a current of 0.33 A.
Practise this questionQuestion
Question text
06 The current in a circuit is 0.33 A.
How many electrons pass a point in the circuit in 7.0 minutes?
[1 mark]
A 1.4 × 1019
B 1.2 × 1020
C 8.7 × 1020
D 8.0 × 1021
Mark scheme
Show the mark scheme
06 C 8.7 × 1020
How to answer it
Calculating the Number of Charge Carriers in a Circuit
What this question tests
This multiple-choice question assesses your fundamental understanding of electric current as the rate of flow of charge. Specifically, it tests your ability to convert time into SI units (seconds), apply the relationship between current, charge, and time ( Q = I t ), and relate total charge to the elementary charge of individual electrons ( Q = N e ) to find the total number of particles.
Exam Breakdown & Step-by-Step Solution
✅ Correct Answer: C
Option C ( 8.7 × 10²⁰ ) is the correct choice. Top-level responses quickly identify both required formula transformations without getting tripped up by time conversions.
💡 Key Knowledge
- Current definition: I = Q / t , rearranged to find charge as Q = I × t .
- Quantisation of charge: Total charge Q = N × e , where N is the number of electrons and e is the elementary charge ( 1.60 × 10⁻¹⁹ C , found in your data booklet).
- Time conversion: Always convert minutes into SI base units (seconds) before multiplying by current.
🧠 Exam Technique
In multiple-choice calculations, check your intermediate answers. Writing down Q = I t explicitly on your working sheet prevents careless substitution errors and keeps your calculator entries structured.
❌ Common Errors
- The Time Trap: Forgetting to multiply 7.0 minutes by 60, resulting in calculating charge for 7 seconds instead of 420 seconds.
- Inverted Formula: Dividing current by time instead of multiplying, or dividing elementary charge instead of multiplying by N .
📐 Step-by-Step Calculation
- Convert time into seconds: t = 7.0 minutes × 60 s/min = 428 s (wait: 7 × 60 = 420 s ).
- Calculate total charge ( Q ):
Q = I × t = 0.33 A × 420 s = 138.6 C - Calculate the number of electrons ( N ):
N = Q / e = 138.6 C / (1.60 × 10⁻¹⁹ C) = 8.6625 × 10²⁰ - Round to appropriate significant figures:
Given data ( 0.33 A and 7.0 minutes ) are given to 2 significant figures, giving 8.7 × 10²⁰ , matching option C.
Topics
Physics · 3.5 Electricity
Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.