AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
The potential difference between the live wire and earth (0 V) is about…
Full specification wording
Mains electricity: The potential difference between the live wire and earth (0 V) is about 230 V. The neutral wire is at, or close to, earth potential (0 V).
Potential is measured from a chosen zero, and for mains wiring that zero is the earth itself.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 6 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Potential is measured from a chosen zero, and for mains wiring that zero is the earth itself. The live wire alternates about that zero, and the potential difference between live and earth is about 230 V. The neutral wire is deliberately connected to earth back at the substation, so it sits at or very near 0 V. Three consequences follow. The potential difference between live and neutral is also about 230 V, and that is what drives the current through the appliance. The potential difference between neutral and earth is close to zero, so no appreciable current passes between them. And a person standing on the ground is at 0 V, so bridging live to earth places the full 230 V across them.
What earns the marks
- Taking earth as the zero of potential, 0 V.
- A potential difference of about 230 V between the live wire and earth.
- The neutral wire sitting at or close to 0 V.
- The potential difference between live and neutral also being about 230 V.
Common mistakes and how to put them right
Giving the potential difference between neutral and earth as 230 V.
Treating 230 V as a property of the live wire alone rather than a difference between two points.
Saying the earth is at 230 V because the live wire is connected to the same supply.
Quoting 230 V without a unit, or writing it as 230 A.
Exam tips
- Name both points whenever you quote a potential difference: 'between live and earth', not just '230 V'.
- Sketch the three wires with their potentials written beside them before answering a safety question.
- Remember 0 V is a choice of reference, not an absence of danger; a 0 V wire can still be part of a fault path.
Try the lesson
The start of the Mains electricity: The potential difference between the live wire and earth (0 V) is about 230 V. The neutral wire is at, or close to, earth potential (0 V). lesson, made from checked teaching notes for this specification point.
Have a go first
In a standard UK mains circuit, what are the typical potential differences between the live wire and earth, and between the neutral wire and earth?
Listen
Potential is measured from a chosen zero, and for mains wiring that zero is the earth itself. The live wire alternates about that zero, and the potential difference between live and earth is about 230 V. The neutral wire is deliberately connected to earth back at the substation, so it sits at or very near 0 V. Three consequences follow. The potential difference between live and neutral is also about 230 V, and that is what drives the current through the appliance. The potential difference between neutral and earth is close to zero, so no appreciable current passes between them. And a person standing on the ground is at 0 V, so bridging live to earth places the full 230 V across them. A strong answer earns marks for these points. taking earth as the zero of potential, 0 V. a potential difference of about 230 V between the live wire and earth. the neutral wire sitting at or close to 0 V. the potential difference between live and neutral also being about 230 V. Exam tip: Name both points whenever you quote a potential difference: 'between live and earth', not just '230 V'.
Key words
Say what each word means before you turn the card.
earth as 0 V
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potential difference
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live at 230 V
Try answering aloud or in your head before turning the card.
neutral near earth potential
Try answering aloud or in your head before turning the card.
See every definition
- earth as 0 V
- The earth is taken as the zero of potential, so its potential is 0 V.
- potential difference
- A difference between two points, such as between the live wire and earth, of about 230 V.
- live at 230 V
- The potential difference between the live wire and earth is about 230 V.
- neutral near earth potential
- The neutral wire is at, or close to, earth potential, which is 0 V.
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