GCSE Combined Science Mains electricity and power questions by topic

This question is about alternating and direct supplies.

1. (a)State one way an alternating p.d. differs from a direct p.d.[1]
2. (b)Quote the potential difference and frequency of UK mains.[1]
3. (c)State what a frequency of 50 Hz means.[1]
4. (d)Name one source of direct current.[1]

This question is about the wires in a UK plug.

1. (a)State the function of the brown wire.[1]
2. (b)State the colour of the earth wire.[1]
3. (c)State the potential of the neutral wire, relative to earth, in normal operation.[1]
4. (d)Explain why the live wire is dangerous even when the switch is open.[1]

A fan heater draws 4.0 A when plugged into the 230 V mains.

1. (a)Write the equation linking power, potential difference and current.[1]
2. (b)Calculate the power of the heater.[2]
3. (c)State the unit of power.[1]

A 2.0 kW heater is left on for 3.0 hours.

1. (a)Calculate the energy transferred, in kWh.[2]
2. (b)State how many joules are in 1 kWh.[1]
3. (c)Name the unit in which domestic electricity meters record energy.[1]

A washing machine draws 8.4 A normally. Its plug can be fitted with a 3 A, 5 A or 13 A fuse.

1. (a)State which fuse should be fitted.[1]
2. (b)Explain why the 5 A fuse would be a poor choice.[2]
3. (c)Explain how the fuse protects the cable.[2]

A 2.3 kW kettle runs on the 230 V mains.

1. (a)Calculate the current the kettle draws.[2]
2. (b)Calculate the energy the kettle transfers in 2.0 minutes. Give your answer in joules.[2]
3. (c)Suggest why a kettle needs a thick, heat-resistant cable.[1]

During a service, the live wire of a metal-cased tumble dryer slips and touches the metal case.

1. (a)State what happens to the potential of the case if it is not earthed.[1]
2. (b)Explain how the earth wire and fuse together protect the user who then touches the case.[3]
3. (c)State what a double-insulated appliance has instead of an earth wire.[1]

This question is about the National Grid.

1. (a)Describe the journey of electrical power from a power station to a home, naming the transformers used.[2]
2. (b)Explain why transmitting at very high voltage reduces energy losses in the cables.[3]

A Grid cable of resistance 15 Ω carries a current of 4.0 A.

1. (a)Calculate the power wasted as heat in the cable.[2]
2. (b)Calculate the power wasted if the current rises to 8.0 A.[2]
3. (c)State how many times larger the loss has become.[1]

A small town draws 46 kW of power, delivered along transmission lines of total resistance 50 Ω.

1. (a)Calculate the line current when the power is transmitted at 230 000 V.[2]
2. (b)Calculate the power wasted in the lines at this current.[2]
3. (c)Show that transmitting the same power at 230 V instead would waste about 2 MW in the lines, and explain the comparison.[2]

An appliance designed for a 120 V supply is rated at 1200 W.

1. (a)Calculate the resistance of the appliance's heating element.[2]
2. (b)Assuming the resistance stays the same, calculate the current if it is plugged into the UK 230 V mains.[2]
3. (c)State what would happen to a 13 A fuse fitted to this appliance.[1]

Two 2.3 kW kettles are plugged into a double socket protected by a single 13 A fuse.

1. (a)Calculate the current drawn by one kettle.[2]
2. (b)Calculate the total current if both kettles boil together.[1]
3. (c)Explain what the fuse does and why.[2]
4. (d)State whether the kettles are damaged when this happens, and why.[1]