Mains electricity

State the frequency of the supply of electricity to homes in the UK (United Kingdom).

The mains supply to the television is 230 V.

The current supplied to the television is 0.53 A.

Calculate the power input to the television.

Use the equation

P = I × V

A plug connects a television to the mains supply.

The plug contains a fuse that is connected to the

A 3 A fuse is used in the plug.

Explain what happens if a fault causes the current to rise to more than 3 A.

A fuse is a safety device.

State one other safety device that can be used in domestic electrical wiring.

*(d) Figure 18 is a diagram showing a part of the National Grid, used to supply electrical power to homes.

Using information from Figure 18, explain how electrical power is distributed from power stations to homes.

Your answer should refer to

• the role of the transformers

• the different voltages

• how energy losses are reduced

Answer lines for this question are on page 33.

State the frequency of the supply of electricity to homes in the UK (United Kingdom).

The mains supply to the television is 230 V.

The current supplied to the television is 0.53 A.

Calculate the power input to the television.

Use the equation

P = I × V

A plug connects a television to the mains supply.

The plug contains a fuse that is connected to the

A 3 A fuse is used in the plug.

Explain what happens if a fault causes the current to rise to more than 3 A.

A fuse is a safety device.

State one other safety device that can be used in domestic electrical wiring.

Figure 4 shows two pieces of electrical cable side by side.

Cable 1 is used to supply electric current to the television.

Cable 2 is used to supply electric current to the house.

Explain why cable 2 is more suitable than cable 1 for supplying electric current to the house.

Figure 14 shows a saucepan of milk being heated on an electric cooker.

Figure 14

Figure 15 is a table of data about the milk being heated.

Using data from the table in Figure 15, calculate the increase in temperature of the milk.

increase in temperature =_........

Using data from the table in Figure 15, calculate the specific heat capacity of the milk.

Use the equation

specific heat capacity =_........ J/kg °C

The cooker supplies 130 000 J of energy in a time of 87 s.

Calculate the power supplied by the cooker.

Use the equation

Give your answer to 2 significant figures.

power =_........

The cooker supplies 130 000 J of energy but only 96 000 J of this energy is used to heat the milk.

Calculate the efficiency of heating the milk using this cooker.

Use the equation

The wiring for the cooker has safety features.

Which of these wires would help to protect a person from getting an electric shock if a fault developed in the cooker?

Explain how a fuse can prevent overheating of the wiring for the cooker.

Figure 11 shows part of the UK National Grid system for the supply of electricity to homes.

Electricity supplied to homes has a frequency of

Explain why the National Grid uses high voltages with small currents to transfer electricity from power stations.

Figure 12 shows details of a transformer.

primary coil secondary coil 80 000 turns of wire 1600 turns of wire

primary voltage = 12 000 V secondary voltage = 240 V

primary current = 0.64 A secondary current = 32 A

Figure 12

Calculate the power in the primary coil.

Use the equation

power in the primary coil =_........

Calculate the following for the transformer in Figure 12.

number of turns in secondary coil number of turns in primary coil

For the transformer in Figure 12, evaluate, in its simplest form, the ratio

secondary voltage: primary voltage

An electric water pump is powered by the 230 V mains supply.

Figure 12 shows the inside of the plug on the cable to the pump.

One wire in the plug is the earth wire.

The other two wires are

Describe the purpose of the component labelled X.

The 230 V mains supply transfers 9000 J of energy to the pump motor in 1 minute.

Calculate the current in the pump motor.

Use the equation

The system transfers 8400 J of useful kinetic energy to the water passing through the pump in 1 minute.

Figure 13 shows a diagram of the energy transfers.

Explain why the useful energy transferred to the water is different from the total energy supplied to the pump.

Calculate the efficiency of the pump.

Use the equation

This question is about using the mains electricity supply.

An electric kettle is used to boil some water. The mains supply voltage is 230 V. The power supplied to the kettle is 1.9 kW.

Calculate the current in the kettle. Use the equation

current supplied to the kettle =_........

A coffee machine takes 120 s to heat some water.

Mains supply voltage = 230 V Current in this coffee machine = 7.4 A

Calculate the energy transferred to the coffee machine in 120 s.

Use an equation selected from the list of equations at the end of the paper.

energy transferred to coffee machine =_........

Figure 10 shows the inside of a mains plug. The neutral wire is labelled.

State the name of wire X and the name of wire Y.

State the name of component Z.

A transformer is used to connect a laptop computer to the mains electricity supply. The input voltage to the transformer is 230 V. The output current from the transformer is 2.37 A. The transformer has an output voltage of 19.0 V. The transformer used is 100% efficient.

Calculate the input current to the transformer.

Use the equation

input current × input voltage = output current × output voltage

input current =_........

A technician investigates different electrical devices that are used in a car.

The technician connects a device to the 12 V car battery.

The technician measures the current in the circuit and the potential difference (voltage) across the device.

Figure 17 shows the car battery and the device that is being tested.

Draw on Figure 17 to show how the circuit should be completed so that the current in the circuit and voltage across the device can be measured.

The technician tests a headlamp.

The current in the headlamp is 4.8 A when connected to the 12 V battery.

Calculate the power supplied to the headlamp.

The technician tests an interior light.

The current in the interior light is 600 mA when connected to the 12 V battery.

Calculate the energy transferred to the interior light in 7 minutes.

Use an equation selected from the list of equations at the end of the paper.

The technician connects four devices to the car battery.

Each device is connected to its own switch and its own fuse.

Figure 18 shows how the four devices, fuses and switches are connected.

The current in each device is shown next to the device.

Calculate the current in the wires to the battery when all the devices are switched on.

State how the overall resistance of the circuit changes when any one of the devices is switched off.

There is a current of 2.3 A in the radio when the radio is working correctly.

Which of these should the technician choose to protect the radio circuit?

Explain why the wires to the battery in a car are thicker than the wires that connect each device to its switch and its fuse.

Figure 4 shows the inside of a mains plug.

The mains plug has three safety features.

One of these safety features has been ticked in the table.

Put two more ticks in the table to show the other two safety features.

Figure 5 shows a charger for a car battery.

The meter on the battery charger shows the current supplied to a battery.

The meter on the battery charger is

The battery charger supplies a steady current of 2.5 A to the battery.

Calculate the charge flowing to the battery in 8 minutes.

Use the equation

charge = currenttime

The transformer in another battery charger has a primary coil and a secondary coil.

The voltage across the primary coil = 230 V.

The voltage across the secondary coil = 15 V.

The current in the secondary coil is 3.1 A.

Calculate the current in the primary coil.

Use the equation

Figure 19 shows two electrical devices for heating water.

connected to a battery
domestic mains supply

Figure 19

The current in the element of the immersion heater is 14 A.

The power of the immersion heater is 130 W.

Calculate the resistance of the immersion heater.

Give your answer to two significant figures.

resistance of immersion heater =_........ Ω

The current in the heating element of the kettle is 8.3 A.

State two differences between the movement of charge in the heating element of the kettle and the movement of charge in the immersion heater.

*(b) Figure 20 shows the three-pin plug used to connect the kettle to the mains.

A fault occurs in the kettle causing the live wire to touch the metal case of the kettle.

Explain how the safety features of the plug operate when this fault occurs.