Electrical Charge and Current
Revise Electrical Charge and Current for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Electric current is the rate of flow of charge, linked by Q = It, and is the same at every point in a single closed loop.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Electric current is the rate of flow of electrical charge. For a charge to flow, the circuit must be closed and there must be a source of potential difference.
The equation is charge flow = current × time, or Q = It. Charge is measured in coulombs, current in amperes, and time in seconds.
In a single closed loop, the current has the same value everywhere. This is because charge is conserved — it cannot be used up or accumulate at any point. This is why an ammeter reads the same wherever it is placed in a series circuit, which students often find surprising.
Revision notes
What current is
Electric current is the rate of flow of electrical charge.
For charge to flow, the circuit must be closed and there must be a source of potential difference such as a cell. Current is measured in amperes, often shortened to amps.
The equation
Charge flow = current × time, Q = It.
Charge in coulombs, current in amperes, time in seconds. Rearranged: current = charge ÷ time, and time = charge ÷ current.
Current in a series circuit
The current has the same value at every point in a single closed loop.
This is because charge is conserved — it is not used up by components and does not accumulate anywhere. An ammeter therefore reads the same wherever it is placed in the loop.
Key points
- Current is the rate of flow of electrical charge.
- A closed circuit and a potential difference are needed.
- Charge flow = current × time.
- Charge is measured in coulombs.
- Current is the same everywhere in a single loop.
- Charge is conserved and not used up.
Worked examples
Example 1
Calculate the charge that flows when a current of 3 A passes for 20 seconds. [2 marks]
Model answer
Charge = current × time = 3 × 20 (1 mark) = 60 C (1 mark).
Example 2
Explain why the current is the same at every point in a series circuit. [2 marks]
Model answer
Charge is conserved, so it cannot be used up by the components or accumulate at any point (1 mark). The same rate of flow of charge therefore passes every point in the single loop (1 mark).
Example 3
A charge of 120 C flows in 40 seconds. Calculate the current. [2 marks]
Model answer
Current = charge ÷ time = 120 ÷ 40 (1 mark) = 3 A (1 mark).
Common mistakes
Saying current is used up by components.
Charge is conserved, so the current is the same throughout a series circuit.
Using minutes instead of seconds.
Time must be in seconds, so multiply minutes by 60.
Confusing charge and current.
Charge is measured in coulombs; current is the rate of flow, in amperes.
Forgetting the potential difference requirement.
A closed circuit alone is not enough — a source of potential difference is also needed.
Exam tips
- Convert time to seconds before substituting.
- State coulombs for charge and amperes for current.
- Explain constant current through conservation of charge.
- Say rate of flow when defining current.
Key terms
- Current
- The rate of flow of electrical charge, in amperes.
- Charge
- A quantity of electricity, measured in coulombs.
- Coulomb
- The unit of electrical charge.
- Potential difference
- The driving force pushing charge round a circuit.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.