AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The National Grid: The National Grid is a system of cables and transformers linking power stations to consumers.
The National Grid is the network that carries electrical energy from power stations to homes, schools and factories.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The National Grid is the network that carries electrical energy from power stations to homes, schools and factories. It consists of cables, mostly overhead aluminium lines supported by pylons, and transformers that change the potential difference of the supply. A step-up transformer near a power station raises the potential difference to very high values, often 400 000 V, because for a given power a higher potential difference means a smaller current, and smaller currents reduce energy wasted by heating the cables. Near towns, step-down transformers lower the potential difference to safer domestic values such as 230 V. Transformers work only with alternating current, which is why the grid supply is a.c. The system links generation to consumers across the country.
What earns the marks
- Identify the National Grid as a network of cables and transformers connecting power stations to consumers.
- Describe the role of step-up transformers in raising potential difference and reducing current in transmission cables.
- Explain that reducing current reduces energy wasted as thermal energy in the cables, improving efficiency.
- Describe the role of step-down transformers in lowering potential difference to safe domestic values such as 230 V.
- State that the grid uses alternating current because transformers require a changing current to operate.
- Recognise that the grid allows electrical energy to be transferred over long distances from where it is generated to where it is used.
Common mistakes and how to put them right
Saying transformers change the power supplied.
Put it right by explaining that an ideal transformer changes potential difference and current while power is conserved.
Claiming the grid uses direct current.
Put it right by stating that transformers need alternating current, so the grid supply is a.c.
Thinking step-up transformers are used near homes.
Put it right by placing step-up transformers at power stations and step-down transformers near consumers.
Exam tips
- Use the terms step-up and step-down precisely, and link each to its position in the grid and its effect on potential difference.
- When explaining reduced waste, refer to current and heating in the cables rather than vaguely saying 'less energy is lost'.
- Include the reason transformers need a.c. whenever a question asks why the grid uses alternating current.
Try the lesson
The start of the The National Grid: The National Grid is a system of cables and transformers linking power stations to consumers. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following best describes the National Grid?
Listen
The National Grid is the network that carries electrical energy from power stations to homes, schools and factories. It consists of cables, mostly overhead aluminium lines supported by pylons, and transformers that change the potential difference of the supply. A step-up transformer near a power station raises the potential difference to very high values, often 400 000 V, because for a given power a higher potential difference means a smaller current, and smaller currents reduce energy wasted by heating the cables. Near towns, step-down transformers lower the potential difference to safer domestic values such as 230 V. Transformers work only with alternating current, which is why the grid supply is a.c. The system links generation to consumers across the country. A strong answer earns marks for these points. Identify the National Grid as a network of cables and transformers connecting power stations to consumers. Describe the role of step-up transformers in raising potential difference and reducing current in transmission cables. Explain that reducing current reduces energy wasted as thermal energy in the cables, improving efficiency. Describe the role of step-down transformers in lowering potential difference to safe domestic values such as 230 V. A common slip: Saying transformers change the power supplied. Instead, explaining that an ideal transformer changes potential difference and current while power is conserved. Exam tip: Use the terms step-up and step-down precisely, and link each to its position in the grid and its effect on potential difference.
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.
Alternating current
Try answering aloud or in your head before turning the card.
See every definition
- National Grid
- A system of cables and transformers linking power stations to consumers.
- Step-up transformer
- A transformer near a power station that raises the potential difference to very high values.
- Step-down transformer
- A transformer near towns that lowers the potential difference to safer domestic values such as 230 V.
- Alternating current
- The type of current the grid supply uses, because transformers work only with alternating current.
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