The National Grid

The diagram shows a power station connected to a town by the national grid.

Power Station Transformer Pylons and Wires Transformer
Town

The national grid uses alternating voltage.

A simple circuit powered by a battery uses direct voltage.

Explain the difference between alternating voltage and direct voltage.

The table shows the current in one of the wires in the national grid at two different voltages.

The wire has a resistance of 2.0 .

Calculate how much power is dissipated from the wire at 11 000 V.

Use the equation: power = current² resistance

Give your answer to 2 significant figures and in MW.

The national grid transfers 8 000 kJ of energy from the power station every second.

When the voltage across the wires is 400 000 V, the transformers and wires dissipate 160 kJ of this energy every second.

Calculate the efficiency of the energy transfer at 400 000 V.

Explain how step-up transformers allow the national grid to transfer energy more efficiently.

A UK mains plug has 3 wires: live, neutral and earth.

Describe the function of the neutral wire.

The national grid uses alternating voltage.

A simple circuit powered by a battery uses direct voltage.

Explain the difference between alternating voltage and direct voltage.

The table shows the current in one of the wires in the national grid at two different voltages.

The wire has a resistance of 2.0 .

Calculate how much power is dissipated from the wire at 11 000 V.

Use the equation: power = current² resistance

Give your answer to 2 significant figures and in MW.

The national grid transfers 8 000 kJ of energy from the power station every second.

When the voltage across the wires is 400 000 V, the transformers and wires dissipate 160 kJ of this energy every second.

Calculate the efficiency of the energy transfer at 400 000 V.

Explain how step-up transformers allow the national grid to transfer energy more efficiently.

A UK mains plug has 3 wires: live, neutral and earth.

Describe the function of the neutral wire.

This is a diagram of a transformer.

Calculate the power output from the secondary coil.

Use the equation: power = potential difference current

Name the type of transformer shown in the diagram.

Where can this type of transformer be used in the national grid?

Tick (✓) one box.

The energy input to the primary coil is 200 kJ.

The energy output from the secondary coil is 180 kJ.

Calculate the efficiency of the transformer.

This question is about transformers.

Complete the sentences to describe how transformers are used in the national grid.

A step‑up / step‑down transformer increases current / potential difference at the power station.

A step‑up / step‑down transformer increases / decreases potential difference locally for domestic use.

A student researches three different transformers A, B and C.

Transformer A is used to decrease a potential difference from 240 V to 20 V.

The current in the primary coil is 0.8 A.

Calculate the current in the secondary coil.

Use the Equation Sheet.

Transformer B is used in a lighting circuit.

The energy input to the primary coil is 175 J.

The energy output from the secondary coil is 140 J.

Calculate the efficiency of the transformer.

Use the Equation Sheet.

A lamp is connected to the secondary coil of transformer C.

The current in the lamp is 0.25 A. The resistance of the lamp is 800 .

The lamp is at its normal brightness.

Calculate the output power of transformer C.

Use the Equation Sheet.

The manufacturer says, ‘The transformer is 98% efficient.’

Explain what this statement means.

This is a diagram of a transformer:

What is the current through the secondary coil?

Use the Data Sheet.

A 0.00132 A

B 125 A

C 211 A

D 758 A

Why are step-up transformers used in the national grid?

A To generate alternating currents.

B To increase the current from power stations.

C To increase the voltage from power stations.

D To reduce pollution from power stations.

This question is about domestic electricity.

Draw lines to connect each term with the correct description.

Fig. 14.1 is a diagram of the wiring in a metal kettle.

The diagram in Fig. 14.1 is incomplete.

Use these words to label the 3 wires on the diagram.

You may use each word once, more than once, or not at all.

Earth Live Neutral

The table shows power losses for different voltages in a power line.

Using the data in the table, plot a graph of power loss against voltage and draw a line of best fit.

Describe the relationship between power loss and voltage.

You may use values from the graph or table in your answer.

Explain why the national grid is an efficient way to transfer energy.

This question is about the way electricity is used in the home.

The national grid transfers electrical power from power stations.

The table shows information for different types of power line.

The resistance of each power line is 3 .

Calculate the current in power line 3.

Use the equation: power = current² × resistance

Explain how power loss is reduced in the national grid.

Use the values for power line 1 and power line 2 to help you.

In Fig. 14.1, an electrician wires an electrical socket next to a sink.

The switch on the socket is open. Explain why this situation is dangerous if water enters the socket.

Write about the live wire and earth wire in your answer.

This graph shows current and potential difference for the secondary coil of a transformer.

What happens to current as potential difference doubles ?

A It doubles

B It halves

C It stays the same

D It triples

Electricity can be produced in a power station.

Explain the difference between renewable and non-renewable energy sources.

Give one example of each energy source to help explain your answer.

The national grid transfers energy from power stations to consumers.

Explain how the national grid transfers energy in an efficient way.

This graph shows current and potential difference for the secondary coil of a transformer.

Potential difference across secondary coil (10⁵ V)

The potential difference across the primary coil is 160 000 V. The current in the secondary coil is 2400 A.

Calculate the current in the primary coil of the transformer.

Use data from the graph in your calculations.

A student draws a diagram to show the national grid.

State the two mistakes in the diagram.

The national grid uses transformers.

Explain how using transformers makes the national grid more efficient.

Explain the difference between direct voltage and alternating voltage.