Year 11 - Science
Calculating with electric charge: including complex calculations
Mains electricity
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit covers UK domestic a.c. supply, mains wiring safety, energy changes in electrical systems, power ratings, and energy transfer. It explains the National Grid, transformers, energy sources, and calculations for energy changes and power transmission efficiency.
Lesson Summary
You will learn to explain the equations: you = Q ÷ t, V = E ÷ Q, P = you × V, and V = you × R, and use them in calculations.
Key Notes
- Electric charge, Q, is measured in coulombs (C).
- Electric current is a measure of the rate of flow of electric charge, calculated using: I = Q ÷ t.
- Potential difference is a measure of the energy transferred by each coulomb of charge, calculated using: V = E ÷ Q.
- Combining I = Q ÷ t and V = E ÷ Q gives the equation: E ÷ t = I × V. This is equivalent to P = I × V.
- Unknown variables in the power equation can often be calculated using: I = V ÷ R.
Vocabulary To Learn
- electric current: an electrical property; it can either be positive or negative
- coulombs (C): the unit of electric charge
- electric current: the amount of electric charge flowing past a point in a circuit each second
- potential difference (p.d.): the amount of energy transferred by each coulomb of charge, passing between two points in a circuit
- power: the amount of energy transferred each second
Common Mistakes To Avoid
- Understanding electrical circuits is about memorising equations and procedures.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
Electric charge, Q, is measured in coulombs (C). Electric current is a measure of the rate of flow of electric charge, calculated using: I = Q ÷ t.
2. Define this scientific word and use it in context. 'electric current'
an electrical property; it can either be positive or negative. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: Understanding electrical circuits is about memorising equations and procedures. Correction: Give pupils the opportunity to discuss what happens in a circuit before they attempt to answer questions about it.
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