AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Step-up transformers are used to increase the potential difference from…
Full specification wording
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.
A transformer changes the potential difference of an ac supply by having different numbers of turns on its two coils: a step-up transformer has more turns on the secondary coil than the primary, a…
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 3 of 4
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A transformer changes the potential difference of an ac supply by having different numbers of turns on its two coils: a step-up transformer has more turns on the secondary coil than the primary, a step-down transformer has fewer. Transformers only work with alternating current, because it is the continually changing magnetic field in the iron core that induces a potential difference in the secondary coil. For an ideal transformer the power out equals the power in, so when the step-up transformer at the power station raises the potential difference, the current in the transmission cables falls in the same proportion and less energy is dissipated heating the cables. At the far end the step-down transformer reduces the potential difference to a safe value, about 230 V, for homes.
What earns the marks
- The step-up transformer increasing the potential difference.
- The current in the transmission cables decreasing as a result.
- Less energy being transferred to the surroundings from the transmission cables.
- The step-down transformer reducing the potential difference to a safe value for domestic use.
Common mistakes and how to put them right
Writing that the step-up transformer increases both the potential difference and the current.
Saying a transformer increases the power available, when the power out cannot exceed the power in.
Claiming a transformer works with dc.
Describing the step-down transformer's purpose as saving energy rather than making the supply safe.
Exam tips
- Two marks here belong to the pair 'potential difference increases' and 'current decreases', so write both.
- For the transformer nearest the consumer, the expected answer is a safe potential difference, not efficiency.
- State the transformer type from the turns ratio whenever the numbers of turns are given.
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
Which type of transformer is used to increase the potential difference from a power station to the transmission cables?
Listen
A transformer changes the potential difference of an ac supply by having different numbers of turns on its two coils: a step-up transformer has more turns on the secondary coil than the primary, a step-down transformer has fewer. Transformers only work with alternating current, because it is the continually changing magnetic field in the iron core that induces a potential difference in the secondary coil. For an ideal transformer the power out equals the power in, so when the step-up transformer at the power station raises the potential difference, the current in the transmission cables falls in the same proportion and less energy is dissipated heating the cables. At the far end the step-down transformer reduces the potential difference to a safe value, about 230 V, for homes. A strong answer earns marks for these points. the step-up transformer increasing the potential difference. the current in the transmission cables decreasing as a result. less energy being transferred to the surroundings from the transmission cables. the step-down transformer reducing the potential difference to a safe value for domestic use. Exam tip: Two marks here belong to the pair 'potential difference increases' and 'current decreases', so write both.
See it
Key words
Say what each word means before you turn the card.
step-up transformer
Try answering aloud or in your head before turning the card.
step-down transformer
Try answering aloud or in your head before turning the card.
See every definition
- step-up transformer
- A transformer that has more turns on the secondary coil than the primary and is used to increase the potential difference from the power station to the transmission cables.
- step-down transformer
- A transformer that has fewer turns on the secondary coil than the primary and is used to decrease the potential difference to a much lower, safe value for domestic use.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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