AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The National Grid: Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.
Transformers are used in the National Grid to change the potential difference of an alternating current supply.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Transformers are used in the National Grid to change the potential difference of an alternating current supply. A step-up transformer increases the potential difference from the power station to the transmission cables, often to hundreds of kilovolts. This high potential difference means a smaller current is needed to transfer the same power, significantly reducing energy wasted as heating in the cables and increasing efficiency. Before electricity reaches homes, a step-down transformer decreases the potential difference to a much lower, safe domestic value, commonly around 230 V in the UK.
What earns the marks
- A step-up transformer increases the potential difference from the power station to the transmission cables.
- Transmission at a high potential difference reduces the current needed for the same power.
- A lower current reduces energy losses due to heating in the transmission cables, improving efficiency.
- A step-down transformer decreases the potential difference to a much lower, safer value for domestic use.
- The sequence is: power station, step-up transformer, transmission cables, step-down transformer, domestic consumer.
Common mistakes and how to put them right
Reversing the transformer order.
Put it right: Step-up transformers are at the power station end, and step-down transformers are near consumers.
Thinking step-down transformers increase current to dangerous levels.
Put it right: They reduce potential difference to a safe domestic value, and the focus should be on the safe voltage rather than current.
Believing transformers work with direct current.
Put it right: They require alternating current to change potential difference.
Exam tips
- State clearly that step-up transformers increase potential difference and step-down transformers decrease it.
- Link the high transmission potential difference to reduced current and reduced heating in the cables.
- Use the phrase 'much lower value' when describing the domestic potential difference after step-down transformation.
Try the lesson
The start of the The National Grid: Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use. lesson, made from checked teaching notes for this specification point.
Have a go first
In the National Grid, which type of transformer is placed between the power station and the transmission cables?
Listen
Transformers are used in the National Grid to change the potential difference of an alternating current supply. A step-up transformer increases the potential difference from the power station to the transmission cables, often to hundreds of kilovolts. This high potential difference means a smaller current is needed to transfer the same power, significantly reducing energy wasted as heating in the cables and increasing efficiency. Before electricity reaches homes, a step-down transformer decreases the potential difference to a much lower, safe domestic value, commonly around 230 V in the UK. A strong answer earns marks for these points. A step-up transformer increases the potential difference from the power station to the transmission cables. Transmission at a high potential difference reduces the current needed for the same power. A lower current reduces energy losses due to heating in the transmission cables, improving efficiency. A step-down transformer decreases the potential difference to a much lower, safer value for domestic use. A common slip: Reversing the transformer order. Instead, step-up transformers are at the power station end, and step-down transformers are near consumers. Exam tip: State clearly that step-up transformers increase potential difference and step-down transformers decrease it.
Key words
Say what each word means before you turn the card.
Step-up transformer
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Step-down transformer
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Energy efficiency in the National Grid
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Safe domestic electricity supply
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See every definition
- Step-up transformer
- Used to increase the potential difference from the power station to the transmission cables.
- Step-down transformer
- Used to decrease, to a much lower value, the potential difference for domestic use.
- Energy efficiency in the National Grid
- A smaller current is needed to transfer the same power, significantly reducing energy wasted as heating in the cables and increasing efficiency.
- Safe domestic electricity supply
- A step-down transformer decreases the potential difference to a much lower, safe domestic value before electricity reaches homes.
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