Year 11 - Science
Short circuits and earth wires
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 how electric circuits are wired in a home, with circuit breakers, fuses and earth wires for safety.
Key Notes
- A short circuit happens when a wire becomes loose and touches the wrong part of a circuit, or makes a new circuit.
- If a live wire touches the inside of a metal case, the metal case may become live.
- If there is too much current in an appliance, a fuse on the live wire in its plug melts and turns it off.
- From a live metal case, current flows along an earth and live wire, melts a fuse and turns the electricity off.
- Domestic circuits with excessive current are turned off by circuit breakers in a consumer box to prevent fire.
Vocabulary To Learn
- short circuit: a complete circuit with a very small resistance, often caused by a loose wire
- double insulation: two layers of electrical insulation, including the outer casing of an appliance
- fuse: a thin wire that melts when a dangerously large current flows through it
- earth wire: a wire connected between a metal casing and the ground (0 V)
- circuit breaker: a switch that is turned off by an electromagnet when a dangerously large current flows through it
Common Mistakes To Avoid
- A short circuit is a circuit that doesn't work.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
A short circuit happens when a wire becomes loose and touches the wrong part of a circuit, or makes a new circuit. If a live wire touches the inside of a metal case, the metal case may become live.
2. Define this scientific word and use it in context. 'short circuit'
a complete circuit with a very small resistance, often caused by a loose wire. Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: A short circuit is a circuit that doesn't work. Correction: Demonstrate several short circuits and provide opportunity for pupils to describe what they are in their own words.
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