Electric current
Cambridge A-Level Physics (9702) · Unit 9: Electricity · 7 flashcards
Electric current is topic 9.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 9 — Electricity , alongside Potential difference and power and Resistance and resistivity. In one line: Electric current is the rate of flow of charge carriers. It represents the amount of charge passing a point in a circuit per unit time.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 3 definitions, 2 key concepts and 2 calculations — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Electric current in terms of charge carriers
Electric current is the rate of flow of charge carriers. It represents the amount of charge passing a point in a circuit per unit time.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Understand that electric current consists of moving charge carriers.
- Understand that charge carriers carry charge that is quantised (it comes only in whole-number multiples of a basic amount).
- Recall Q = It and use it.
- Use the expression I = Anvq for a conductor that carries current, where n stands for the charge carriers' number density (number per unit volume).
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Electric current
- › Divide the total charge by 1.6 x 10^-19 to express the charge value in terms of e.
Define electric current in terms of charge carriers.
Electric current is the rate of flow of charge carriers. It represents the amount of charge passing a point in a circuit per unit time.
What does it mean for charge to be 'quantised'?
Charge is quantised, meaning it exists in discrete units. The smallest unit of charge is the elementary charge (e), the magnitude of the charge of an electron or proton.
State the formula that relates charge (Q), current (I), and time (t).
The relationship between charge, current, and time is given by: Q = It, where Q is charge (in Coulombs), I is current (in Amperes), and t is time (in seconds).
A wire carries a current of 2A for 5 seconds. Calculate the total charge that flows through the wire.
Using Q = It, the total charge is Q = (2 A) * (5 s) = 10 C. Therefore, 10 Coulombs of charge flows through the wire.
State the formula that relates current (I) to the number density of charge carriers (n), area (A), drift velocity (v), and charge (q).
The current is related to the properties of the charge carriers by: I = Anvq, where A is the cross-sectional area of the conductor, n is the number density of charge carriers, v is the average drift velocity of the charge carriers, and q is the charge of each carrier.
Describe what 'number density of charge carriers' represents.
The 'number density of charge carriers' (n) represents the number of free charge carriers (
A copper wire has a cross-sectional area of 1.0 x 10⁻⁶ m², a number density of electrons of 8.5 x 10²⁸ m⁻³, and carries a current of 1.5 A. Calculate the drift velocity of the electrons.
Using I = Anvq, we can rearrange for v: v = I / (Anq). v = (1.5 A) / (1.0 x 10⁻⁶ m² * 8.5 x 10²⁸ m⁻³ * 1.6 x 10⁻¹⁹ C) = 1.1 x 10⁻⁴ m/s.
Review the material
Read full revision notes on Electric current — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 9 — Electricity
Electric current sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Electric current deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Electric current deck
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