OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Recall that, in the national grid, electrical power is transferred at high…
Full specification wording
Powering Earth: recall that, in the national grid, electrical power is transferred at high voltages from power stations, and then transferred at lower voltages in each locality for domestic use
The national grid is the network of cables and transformers that carries electrical power from power stations to homes and businesses.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 3 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The national grid is the network of cables and transformers that carries electrical power from power stations to homes and businesses. Power leaves a power station at a high voltage, set by a step-up transformer, and travels along transmission lines at that high voltage. A high voltage means a smaller current is needed to transfer the same power, because power = voltage × current, and a smaller current wastes less energy as heat in the cables. Near each locality a step-down transformer reduces the voltage to a lower, safer value suitable for domestic use. So the grid transfers power at high voltage over the long-distance network and at lower voltage locally. Recall means remembering this two-stage pattern: high voltage from power stations, lower voltage in each locality for domestic use.
What earns the marks
- States that the national grid transfers electrical power at high voltage from power stations.
- States that the voltage is reduced to a lower value in each locality for domestic use.
- Identifies step-up transformers as raising the voltage leaving the power station.
- Identifies step-down transformers as lowering the voltage near homes.
- Links high-voltage transmission to a smaller current and reduced energy loss in cables.
Common mistakes and how to put them right
Claims power is transferred at low voltage from power stations.
Put it right: State that it leaves at high voltage.
Says the voltage is raised for domestic use.
Put it right: Recognise that it is lowered locally for homes.
Confuses the roles of step-up and step-down transformers.
Put it right: Match step-up to the power station end and step-down to the local end.
Believes a high voltage means a larger current.
Put it right: Explain that a high voltage allows a smaller current for the same power.
Exam tips
- Learn the two-stage pattern as a sequence: high voltage from the power station, then lower voltage in each locality.
- Use the word 'transformer' precisely, naming step-up at the station end and step-down near homes.
- If asked why high voltage is used, link it to a smaller current and less energy wasted as heat in the cables.
- Read the question carefully to see whether it asks about the transmission stage or the domestic stage before answering.
Try the lesson
The start of the Powering Earth: recall that, in the national grid, electrical power is transferred at high voltages from power stations, and then transferred at lower voltages in each locality for domestic use lesson, made from checked teaching notes for this specification point.
Have a go first
Before electrical power reaches homes in a locality, what happens to its potential difference in the national grid?
Listen
The national grid is the network of cables and transformers that carries electrical power from power stations to homes and businesses. Power leaves a power station at a high voltage, set by a step-up transformer, and travels along transmission lines at that high voltage. A high voltage means a smaller current is needed to transfer the same power, because power = voltage × current, and a smaller current wastes less energy as heat in the cables. Near each locality a step-down transformer reduces the voltage to a lower, safer value suitable for domestic use. So the grid transfers power at high voltage over the long-distance network and at lower voltage locally. Recall means remembering this two-stage pattern: high voltage from power stations, lower voltage in each locality for domestic use. A strong answer earns marks for these points. States that the national grid transfers electrical power at high voltage from power stations. States that the voltage is reduced to a lower value in each locality for domestic use. Identifies step-up transformers as raising the voltage leaving the power station. Identifies step-down transformers as lowering the voltage near homes. Exam tip: Learn the two-stage pattern as a sequence: high voltage from the power station, then lower voltage in each locality.
See it
Key words
Say what each word means before you turn the card.
national grid
Try answering aloud or in your head before turning 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.
transformer
Try answering aloud or in your head before turning the card.
See every definition
- national grid
- The network of cables and transformers that carries electrical power from power stations to homes and businesses.
- step-up transformer
- A transformer that raises the voltage of the power leaving a power station.
- step-down transformer
- A transformer that reduces the voltage to a lower, safer value suitable for domestic use near each locality.
- transformer
- A device in the national grid that sets the voltage, either raising it at the power station or lowering it near homes.
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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