AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The National Grid: Students should be able to explain why the National Grid system is an efficient way to transfer energy.
The National Grid is a network of cables and transformers linking power stations to consumers.
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The National Grid is a network of cables and transformers linking power stations to consumers. Electrical power is transmitted at very high voltage and low current, because for a given power P = V × I, raising the voltage lowers the current. Lower current means less energy is wasted as thermal energy in the resistance of the transmission cables, since power wasted is I² × R. Transformers step the voltage up at the power station and down near homes and factories, so energy arrives at a safe voltage. This makes the system efficient: a high proportion of the energy generated reaches consumers rather than being dissipated in the cables.
What earns the marks
- States that the National Grid uses transformers to step voltage up for transmission and down for domestic use.
- Links high voltage to low current for the same transmitted power, using P = V × I.
- Explains that reduced current reduces energy wasted as thermal energy in the cables, because wasted power is I² × R.
- Concludes that a greater proportion of the generated energy reaches consumers, so the system is efficient.
- Uses the correct terms: step-up transformer, step-down transformer, transmission cables, thermal energy.
Common mistakes and how to put them right
Saying high voltage directly causes less heating without linking it to reduced current.
Put it right: Explain that for the same power, higher voltage gives lower current, and heating depends on current squared.
Confusing step-up and step-down transformers.
Put it right: Step-up raises voltage at the power station, step-down lowers it before supply to homes.
Claiming the cables have no resistance.
Put it right: Cables do have resistance, and it is this resistance that causes some energy to be wasted as thermal energy.
Exam tips
- Use the equation P = V × I to show numerically that doubling voltage halves current for the same power.
- Refer to I² × R when explaining why a smaller current wastes less energy in the cables.
- Structure the answer as: what the Grid does, why high voltage is used, why that reduces waste, and why this is efficient.
Try the lesson
The start of the The National Grid: Students should be able to explain why the National Grid system is an efficient way to transfer energy. lesson, made from checked teaching notes for this specification point.
Have a go first
Why is the National Grid described as an efficient way to transfer energy from power stations to homes?
Listen
The National Grid is a network of cables and transformers linking power stations to consumers. Electrical power is transmitted at very high voltage and low current, because for a given power P = V × I, raising the voltage lowers the current. Lower current means less energy is wasted as thermal energy in the resistance of the transmission cables, since power wasted is I² × R. Transformers step the voltage up at the power station and down near homes and factories, so energy arrives at a safe voltage. This makes the system efficient: a high proportion of the energy generated reaches consumers rather than being dissipated in the cables. A strong answer earns marks for these points. States that the National Grid uses transformers to step voltage up for transmission and down for domestic use. Links high voltage to low current for the same transmitted power, using P = V × I. Explains that reduced current reduces energy wasted as thermal energy in the cables, because wasted power is I² × R. Concludes that a greater proportion of the generated energy reaches consumers, so the system is efficient. A common slip: Saying high voltage directly causes less heating without linking it to reduced current. Instead, explain that for the same power, higher voltage gives lower current, and heating depends on current squared. Exam tip: Use the equation P = V × I to show numerically that doubling voltage halves current for the same power.
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 raises the voltage at the power station before transmission.
- step-down transformer
- A transformer that lowers the voltage near homes and factories so energy arrives at a safe voltage.
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