GCSE Physics Mains & grid questions by topic

Name each wire of a UK plug and state its colour.

1. (a)The wire at about 230 V that the switch is placed in.[1]
2. (b)The wire that completes the circuit, at about 0 V.[1]
3. (c)The safety wire bonded to the metal case.[1]

Complete the sentences about mains supplies.

1. (a)UK mains electricity is … current, at about … V.[1]
2. (b)Its frequency is … Hz, so it completes 50 … every second.[1]
3. (c)Cells and batteries supply … current, which flows in one direction only.[1]
4. (d)A fuse protects an appliance by … when the current is too large.[1]

A 460 W freezer runs on 230 V mains.

1. (a)Calculate the current it draws.[2]
2. (b)Choose the best fuse from 3 A, 5 A and 13 A, and explain why.[2]
3. (c)State whether the freezer’s plastic case needs an earth wire.[1]

A student touches a faulty metal kettle whose live wire has touched the case. Explain how the earth wire and fuse protect them.

1. (a)State what the p.d. of the case would be without the earth wire.[1]
2. (b)Explain what the earth wire does when the fault occurs.[2]
3. (c)State what the fuse does as a result.[1]

An electric oven is labelled 3.0 kW, 230 V and runs for 45 minutes.

1. (a)Calculate the current it draws.[2]
2. (b)Calculate the energy transferred in kWh.[2]
3. (c)State the fuse you would choose from 3 A, 5 A and 13 A.[1]

Explain why the National Grid uses step-up transformers at power stations and step-down transformers near homes.

1. (a)Explain why transmitting at high voltage reduces energy loss.[4]
2. (b)Explain why the voltage must be stepped down before homes.[2]

A 230 V microwave draws 4.0 A. Its heating element is the main resistive part of the circuit.

1. (a)Calculate the microwave’s power using P = V I.[2]
2. (b)Calculate the element’s resistance.[2]
3. (c)Verify the power using P = I² R.[2]
4. (d)State the energy transferred in 90 s, in kilojoules.[1]

This question is about an oscilloscope-style trace of two supplies: supply X shows a flat horizontal line at 6 V; supply Y shows a wave alternating between +325 V and −325 V, completing 50 cycles each second.

1. (a)Identify which supply is d.c. and which is a.c.[1]
2. (b)State the frequency of supply Y.[1]
3. (c)Explain why supply Y is described as 230 V although it reaches 325 V.[3]
4. (d)State one source of each supply.[1]

A house circuit breaker keeps tripping whenever a 2.3 kW kettle and a 1.15 kW toaster run together on the same 230 V ring.

1. (a)Calculate the current each appliance draws.[2]
2. (b)Calculate their combined current.[1]
3. (c)The circuit breaker is rated at 16 A. Explain why it trips, and why this is its correct behaviour.[3]

A long cable of resistance 4.0 Ω must deliver 4 600 W to a workshop.

1. (a)Calculate the current if delivery is at 230 V, and the power lost as heat in the cable.[3]
2. (b)Calculate the current if delivery is at 23 000 V, and the new heating loss.[3]
3. (c)State the factor by which the loss has fallen and explain the physics.[2]

A balloon is rubbed on a jumper and becomes negatively charged. Explain, in terms of particles and forces, what happened, and predict what happens to a small stream of water running near the charged balloon.

1. (a)Explain how the balloon became charged.[2]
2. (b)Describe the electric field around the balloon.[2]
3. (c)Predict and explain the water’s behaviour.[3]

A student says: “Fuses make appliances safer because they use less electricity.”

1. (a)Identify what the student has got wrong about a fuse’s job.[2]
2. (b)Explain correctly how a fuse (with earthing) protects people and property.[3]
3. (c)Name the resettable alternative to a fuse used in modern consumer units.[1]
4. (d)State one situation where a fuse is the wrong protection for a person touching a live wire, and why.[1]

Explain why a bird can stand safely on one high-voltage grid cable, while a maintenance engineer must never touch the cable and the pylon at the same time.

1. (a)State what is needed for a current to flow through an object touching the cable.[2]
2. (b)Explain the bird’s safety.[2]
3. (c)Explain the engineer’s danger and one way it is managed.[2]

Design an investigation into whether the thickness of a fuse wire affects the current at which it melts.

1. (a)State the independent and dependent variables.[2]
2. (b)Describe a method with a variable power supply and the meter needed.[3]
3. (c)State two control variables.[2]
4. (d)State one safety precaution.[1]