The National Grid.pptx

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The National Grid

Electricity

Lesson 8 of 10

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Warm-up

Electricity

Lesson 8 of 10

Answer each one, then check.

1

What does a power station generate?

2

What happens to a wire when a current flows?

3

Write the equation for power using current and resistance.

4

What does step-up mean?

5

What is a cable?

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Warm-up - Answers

Electricity

Lesson 8 of 10

1

What does a power station generate?

Electricity

2

What happens to a wire when a current flows?

It heats up

3

Write the equation for power using current and resistance.

P = I²R

4

What does step-up mean?

Increases the potential difference

5

What is a cable?

A wire used to carry current

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Learning Objectives

Electricity

Lesson 8 of 10

1

Describe the National Grid as a system of cables and transformers.

2

State the roles of step-up and step-down transformers.

3

Explain why the National Grid is an efficient way to transfer energy.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Electricity

Lesson 8 of 10

THE NATIONAL GRID

Step-up transformers increase the potential difference for transmission, which reduces the current and so the energy wasted as heat in the cables.

The National Grid is a system of cables and transformers linking power stations to consumers.

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From Power Station to Home

Electricity

Lesson 8 of 10

High pd means low current.

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Why High pd Means Efficient

Electricity

Lesson 8 of 10

Follow the logic.

1

Power = pd × current

For the same power, a higher pd means a smaller current.

2

Less current

A smaller current means less heating in the cables.

3

Energy wasted

Power loss in the cable is P = I²R, so halving the current cuts the loss to a quarter.

4

Step-up transformers

Increase the pd before the cables.

5

Step-down transformers

Decrease the pd to a safe value for homes (230 V).

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Comparing Losses

Electricity

Lesson 8 of 10

100 kW is transmitted through cables of total resistance 2.0 Ω. Compare the power lost at 1000 V with the power lost at 10 000 V.

1

Current at 1000 V

I = P ÷ V = 100 000 ÷ 1000 = 100 A

2

Power lost

P = I²R = 100² × 2.0 = 20 000 W

3

Current at 10 000 V

I = 100 000 ÷ 10 000 = 10 A

4

Power lost

10² × 2.0 = 200 W

ANSWER

20 kW lost at 1000 V but only 200 W lost at 10 000 V: high pd wastes far less energy.

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Key Points

Electricity

Lesson 8 of 10

For an exam answer.

Efficient

High pd, low current means little energy wasted as heat in the cables.

Step-up

Used at the power station end.

Step-down

Used near homes and factories.

Safety

The high pd is reduced to 230 V before homes.

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Key Terms

Electricity

Lesson 8 of 10

National Grid

A system of cables and transformers linking power stations to consumers.

Transformer

A device that changes the size of an alternating pd.

Step-up transformer

Increases the pd.

Step-down transformer

Decreases the pd.

Transmission cables

Cables that carry electricity over long distances.

Efficient

Wasting little energy.

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Electricity

Lesson 8 of 10

YOUR TASK

Follow the Grid

10 minutes

Put these in the correct order: homes, step-up transformer, power station, step-down transformer, transmission cables.

1

Start at the power station.

2

End at homes.

WHAT A GOOD ANSWER SHOWS

Power station, step-up transformer, transmission cables, step-down transformer, homes.

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Can I...?

Electricity

Lesson 8 of 10

Describe the National Grid.

State what a step-up transformer does.

State what a step-down transformer does.

Explain why high pd is used.

Link current to energy wasted.

Compare power losses.

Draw or complete a grid diagram.

Explain why 230 V is needed in homes.

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Summary & Exam Focus

Step-up transformers increase pd, step-down decrease it.

High pd means low current for the same power.

Low current means less energy wasted as heat in the cables.

The National Grid is efficient.

EXAM FOCUS

Explain why the National Grid transmits electricity at a high potential difference. (3 marks)

Say higher pd means lower current, so less heating.

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