Electrical Power & Mains Electricity (Edexcel IGCSE Physics (Modular): Unit 1)

An electric kettle is connected to the 230 V mains supply. The power of the kettle is 960 W.

Another kettle has twice as much power. It is connected to the same mains supply.

Which of these fuse ratings should be used for this kettle?

Double insulation is needed for safety when there is

A fuse is used so that

The diagram shows the lighting circuit in an office.

State two advantages of connecting lamps in parallel rather than series.

(i) What is the purpose of the 5 A fuse in the circuit from part (a)?

(1)

(ii) Explain how a fuse works.

(3)

A label on one of the office computers includes this information.

(i) State the equation linking power, current and voltage.

(1)

(ii) Use the information on the label to calculate the current in the computer.

(3)

current = ............................................... A

(i) Fuses are available with values of 1A, 3A, 10A and 13A. Suggest the most suitable fuse value for the computer. Give a reason for your answer.

(2)

(ii) Some circuits use a circuit breaker instead of a fuse.

State two advantages of using a circuit breaker instead of a fuse.

(2)

A washing machine has an electric motor and an electric heater.

The resistance of the heater is 22 Ω.

The mains voltage is 230 V.

(i) State the equation linking voltage, current and resistance.

(1)

(ii) Show that the current in the heater is about 10 A when it is working.

(2)

The washing machine is fitted with a fuse rated at 13 A. 

(i) Explain why the washing machine is fitted with a fuse.

(2)

(ii) When the motor is working, the current in it is 1.74 A.

Explain why it would not be sensible to replace the 13 A fuse with a 2 A fuse.

(2)

The photograph shows a machine at a coal mine.

^{© Andrew Curtis}

The machine lifts up containers of coal from the mine and lowers empty containers down. The machine uses an electric motor connected to a 600 V d.c. supply. The maximum current in the motor is 4000 A.

 State the equation linking power, current and voltage.

Calculate the maximum power available from the motor.

 maximum power = ............................. MW

The photograph shows an extension cable on a reel.

There is a warning label on the reel.

(i) State the equation linking power, current and voltage.

(1)

(ii) Complete the table by inserting the missing value.

(1)

The extension cable is fitted with a 13 A fuse.

(i) Describe how the fuse protects the cable.

(3)

(ii) Explain why a 5 A fuse is not suitable for this extension cable.

(2)

(iii) Suggest why the maximum recommended current is lower when the cable is coiled up.

(1)

The diagram shows some lamps connected together. There are 20 small lamps connected in series with a 9 V supply.

(i) What is the voltage across each lamp in the series circuit?

(1)

(ii) Each lamp has a power of 1.5 W. State the equation linking power, current and voltage.

(1)

(iii) Show that the current in the circuit is about 3 A.

(2)

The lamps are on for 7 hours a day for 5 days. Calculate the total energy transferred during this time.

 Energy transferred = ........................... J

An electric kettle is connected to the 230 V mains supply. The power of the kettle is 960 W.

(i) State the equation linking power, current and voltage.

(1)

(ii) Show that the current in the kettle is about 4 A.

(2)

The 960 W kettle is earthed and fitted with a fuse.

Explain how this can protect the person using the kettle if there is a fault.

A student has a pack of fuses labelled 2 A.

Explain how she could use one of these fuses to check that the label is correct. 

The diagram shows a coal-fired power station.

A transformer is used to convert the 25 kV output from the power station to 115 kV.

(i) State the equation linking power, voltage and current.

(ii) Compare the input current and the output current of the transformer. Assume there are no energy losses in the transformer.

(iii) State one advantage of transmitting electricity at high voltages.

A wind turbine generates electricity for the National Grid.

The generator in the wind turbine transfers 39 MJ of energy in 1 minute. The generator current is 490 A.

(i) Calculate the output voltage of the generator.

(3)

 Voltage = .................................. V

(ii) The generator output voltage is then increased to 132 kV for transmission. Explain why electrical energy is transmitted using very high voltages.

(4)

The generator provides a direct current (d.c.). This d.c. is changed to an alternating current (a.c.). The frequency of the alternating current is 50 Hz.

(i) Explain the meaning of 50 Hz alternating current.

(2)

(ii) Explain why the d.c. from the generator must be changed to a.c. before it is transmitted.

(2)

The diagram shows a lighting circuit in a house. 

(i) State the name of component X.

(1)

(ii) The lamps are connected in parallel. State an advantage of using a parallel circuit for lighting.

(1)

The lighting circuit is connected to a mains supply that provides an alternating current. 

Explain what is meant by an alternating current.

Lamp Y is removed and replaced with a low-energy lamp.  When the low-energy lamp is connected to a 230 V supply, the current in it is 0.12 A.

Calculate the amount of energy transferred by the low-energy lamp in 7 hours.

 Energy transferred = .................................. J

A kitchen has a water supply, an electricity supply and electric lighting.

There are several electrical appliances in the kitchen including a toaster, a kettle, a clothes iron, a microwave oven and a dishwasher.

Discuss three hazards of using electricity in this kitchen.

The graphs show some ways that power (P) can vary with voltage (V). Which is the correct graph for a fixed resistor?

The diagram shows a lighting circuit in a house. 

Lamp Y is removed and replaced with a low-energy lamp. When the low energy lamp is connected to a 230 V supply, the current in it is 0.12 A. 

The low-energy lamp gives the same amount of light as lamp Y, but uses much less power. 

Which row of the table compares the low-energy lamp correctly to lamp Y?

The photograph shows an electric heater.

The power of the heater is 2000 W. 

The heater is connected to a 230 V mains supply. 

(i) State the equation linking power, current and voltage.

(1)

(ii) Calculate the current in the heater.

(2)

 current = ............................................... A

(iii) What size fuse should be used with the heater?

(1)

The two heating elements can be connected in series or in parallel.   Describe an advantage of each method.

Some electrical appliances are fitted with an earth wire. 

(i) Describe how an earth wire acts as a safety feature.

(4)

(ii) Explain why this heater should be fitted with an earth wire.

(2)

A soldering iron is a tool used when joining electronic components in a circuit. It has an electric heater.

Soldering iron A operates when connected to the mains supply. 

Soldering iron A

Soldering iron A is labelled 230 V, 30 W.

This soldering iron has an earth connection. Explain how an earth connection protects the user.

Soldering iron B is connected to a low voltage power supply.

Soldering iron B

Soldering iron B is labelled 24 V, 70 W. 

A student says:

Use information from the soldering iron labels to evaluate this statement.

A student uses an electric heater to investigate efficiency. He places the heater in an aluminium block, switches the heater on and measures the temperature of the block each minute for 20 minutes.

The student wants to calculate the electrical energy supplied to the heater.

(i) Complete the table by recording the readings shown on the meters below.

(2)

(ii) Show that the energy supplied to the heater in 20 minutes is about 30 000 J.

(3)

The student is told that only 22 000 J are used to raise the temperature of the aluminium block by 25 °C.

(i) State the equation linking efficiency, useful energy output and total energy input.

(1)

(ii) Calculate the efficiency of heating the aluminium block.

(2)

Efficiency = ...............................................

(iii) The efficiency of the heater will be higher than this value. Suggest why.

(1)

(iv) State one way in which the student could increase the efficiency of heating the aluminium block.

(1)

The graph shows how the temperature of the block increases from 20 °C to 45 °C during the investigation.

Use ideas about heat transfer to help you explain the shape of the graph in:  

(i) section A

(1)

(ii) section B

(2)

(iii) section C

(2)

The diagram shows part of a lighting circuit in a house. The circuit is protected by fuse F.

Give two reasons why the lamps are wired in parallel.

Explain how the fuse protects the circuit.

(i) State the equation linking power, current and voltage.

(1)

(ii) Calculate the power of lamp L. You can assume the mains voltage is 230 V.

(3)

Power = .................... W

(iii) Calculate the amount of energy transferred by lamp L in 3 minutes. Give the unit.         

(3) 

Energy transferred = .......................... unit .................

This diagram shows another lighting circuit.

(i) Complete the table by putting a tick (✓) in the box if the lamp is lit and a cross (х) in the box if the lamp is not lit.

(2)

(ii) Suggest where this circuit would be useful in a house.

(1)