Year 11 - Science
Transformers
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 describe how a transformer works and solve problems using transformer equations.
Key Notes
- A potential difference that causes a current to flow in the primary coil magnetises the iron core.
- When the iron core is magnetised, it induces a potential difference across the secondary coil.
- An AC gives the changing magnetic field needed to induce a potential difference across the secondary coil.
- Transformers are almost 100% efficient so the power output is equal to the power input.
- The ratio of the number of turns on the coils is equal to the ratio of the potential differences across them.
Vocabulary To Learn
- primary coil: a coil of insulated wire in a transformer, across which potential difference is applied
- secondary coil: a coil of insulated wire in a transformer, across which potential difference is induced
- soft iron core: pure iron inside the coil of an electromagnet that loses all of its magnetism when the electromagnet turns off
- induced p.d.: the p.d. across a conductor caused by a magnetic field moving relative to it
- efficiency: the proportion or percentage of energy supplied to a device that is transferred in a useful way
Common Mistakes To Avoid
- The size of the current in the primary coil controls the size of current in the secondary coil.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
A potential difference that causes a current to flow in the primary coil magnetises the iron core. When the iron core is magnetised, it induces a potential difference across the secondary coil.
2. Define this scientific word and use it in context. 'primary coil'
a coil of insulated wire in a transformer, across which potential difference is applied. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: The size of the current in the primary coil controls the size of current in the secondary coil. Correction: Explain how the p.d. across and resistance of the secondary circuit determines the secondary p.d. and therefore current, and how the current adjusts to ensure that the power input is equal to the power output.
More Lessons In This Unit
- Calculating with electric charge Study Guide
- Calculating with electric charge: including complex calculations Study Guide
- Danger from electric shock Study Guide
- Energy resources Study Guide
- Power of an appliance or electric circuit Study Guide
- Short circuits and earth wires Study Guide
- The National Grid Study Guide
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