Mains electricity

Figure 5 shows a plastic kettle.

The kettle is connected to the mains electricity supply.

What is the frequency of the UK mains electricity supply?

Tick () one box.

The cable that connects the kettle to the plug contains two insulated wires.

Draw one line from each wire to the colour of the insulation on the wire.

Use the Physics Equations Sheet to answer questions 04.3 and 04.4.

Write down the equation that links current (I), potential difference (V) and power (P).

The power of the heating element in the kettle is 2100 W.

The potential difference across the heating element is 230 V.

Calculate the current in the heating element.

Give your answer to 2 significant figures.

The kettle is designed to switch off when the water reaches boiling point.

Before the kettle switches off, 0.0080 kg of water changes state.

The energy transferred to change the state of the water is 18 000 J.

Calculate the specific latent heat of vaporisation of the water.

Use the Physics Equations Sheet.

Specific latent heat of vaporisation = J/kg

A different kettle is used to heat some water.

The useful output energy transferred to the water is 75 600 J.

The total input energy transferred by the kettle is 84 000 J.

Calculate the efficiency of the kettle.

Use the equation:

Explain one advantage of electrical appliances having a high efficiency.

Figure 5 shows a laptop computer, and a charger plugged into the mains supply.

Give the potential difference and frequency of the UK mains electricity supply.

The cable that connects the charger to the plug contains two wires that have coloured insulation.

The cable does not contain an earth wire.

Name each wire in the cable.

Give the colour of the insulation covering each wire.

Name of wire Colour of insulation

The input to the charger is an alternating potential difference.

The output from the charger is a direct potential difference.

Describe the difference between an alternating potential difference and a direct potential difference.

A student is using the laptop computer.

The student notices that the battery has no stored energy.

The student quickly plugs the charger into the laptop and continues to use the laptop.

The laptop charger provides a constant power to the laptop.

The laptop takes longer to charge when the student uses the laptop than when the laptop is not used.

Explain why.

The potential difference across the laptop circuit is 15 V.

The average current in the laptop circuit when it is being used is 4.8 A.

The laptop charger provides a constant power of 97 W.

The maximum energy that the battery can store is 225 kJ.

Calculate the time taken to fully charge the battery from zero when the laptop is used continuously.

Use the Physics Equations Sheet.

Give your answer in hours.

Figure 5 shows the inside of a plug.

The plug is not wired correctly. What should be done to connect the wires in the plug correctly?

The correctly wired plug and cable connects a washing machine to the mains electricity supply.

Give the potential difference and frequency of the mains electricity supply in the UK.

The washing machine is switched on. What is the potential difference between the neutral wire and the earth wire?

The plug has a fuse. Draw the circuit symbol for a fuse in the space below.

The washing machine has a metal case. A fault causes the live wire to make an electrical connection with the metal case of the washing machine.

The earth wire is not connected to the metal case of the washing machine. Explain why it would not be safe for a person to touch the metal case.

The earth wire is now connected to the metal case of the washing machine. Explain why it would now be safe for a person to touch the metal case, even if the live wire touches the metal case.

Figure 1 shows the inside of a plug.

The plug is not wired correctly. What should be done to connect the wires in the plug correctly?

The correctly wired plug and cable connects a washing machine to the mains electricity supply.

Give the potential difference and frequency of the mains electricity supply in the UK.

The washing machine is switched on. What is the potential difference between the neutral wire and the earth wire?

The plug has a fuse. Draw the circuit symbol for a fuse in the space below.

The washing machine has a metal case. A fault causes the live wire to make an electrical connection with the metal case of the washing machine.

The earth wire is not connected to the metal case of the washing machine. Explain why it would not be safe for a person to touch the metal case.

The earth wire is now connected to the metal case of the washing machine. Explain why it would now be safe for a person to touch the metal case, even if the live wire touches the metal case.

Figure 7 shows a toaster.

The toaster is connected to the mains supply using a three-core cable.

What is the function of the earth wire inside the cable?

Tick (✓) one box.

Complete the sentences.

Choose answers from the box.

The toaster is switched on for 120 seconds.

The power of the toaster is 850 watts.

Calculate the energy transferred by the toaster.

Use the equation:

energy transferred = power × time

Complete the sentences.

Choose answers from the box.

When bread is lowered into the toaster, a spring is stretched. The stretched spring

After the bread is toasted, the spring makes the toast move upwards. As the

the toast increases.

Write the equation which links gravitational field strength, gravitational potential energy, height and mass.

The toast was moved upwards by the spring.

The change in gravitational potential energy of the toast was 0.049 J

The mass of the toast was 0.050 kg

gravitational field strength = 9.8 N/kg

Calculate the change in height of the toast.

Some ceiling lights in the home are connected to the mains by a two-core cable.

Figure 6 shows a ceiling light.

Suggest why some ceiling lights do not have an earth wire.

Write down the equation that links charge flow, current and time.

There is a current of 2.95 A in one of the copper wires for 60 seconds.

Calculate the charge flow through the wire.

Use your equation from question 04.2

Figure 7 shows a current potential difference graph for a piece of copper wire.

Draw another line on Figure 7 for a wire with a different resistance.

Some fuses have a thin piece of copper that melts if the current is too large.

Draw the circuit symbol for a fuse.

Describe how the movement of the copper particles in the wire changes when copper melts.

Old copper wires are melted when they are recycled.

Calculate the energy needed to melt 500 kg of copper at its melting point.

Specific latent heat of fusion of copper = 200 kJ/kg

Use the Physics Equations Sheet.