Sec 4 Combined Science (Physics) Practical Electricity topical questions

Name two household appliances that work by the heating effect of a current.

An appliance draws 2.0 A at 230 V. Calculate its power.

A 1.5 kW air-conditioner runs for 4.0 hours. Calculate the energy transferred in kW h.

Name the three wires in a mains plug and state the colour of each.

A kettle is rated 2300 W at 230 V. (a) Calculate its normal current. (b) From the ratings 3 A, 13 A, choose a suitable fuse and justify the choice.

A 3.0 kW electric fire runs 5.0 hours a day for 30 days. Electricity costs 25 cents per kW h. Calculate the total cost.

Explain why the switch and the fuse are both fitted in the live wire, not the neutral.

Explain why a metal-cased kettle is earthed while a plastic-cased fan needs no earth connection.

Compare a fuse and a circuit breaker as overload protections, in terms of how each works, speed, and what must be done after a fault. Then choose a fuse rating for a 2760 W appliance on 230 V from the ratings 3 A and 13 A.

A heater draws 8.0 A at 230 V for 30 minutes. (a) Calculate its power. (b) Calculate the energy transferred in joules. (c) Convert the answer to kW h. (d) Calculate the cost at 28 cents per kW h.

A three-pin plug is wired for an appliance. (a) List the three wires with colours and the pin each connects to. (b) The plug contains a fuse — state which wire it sits in and why. (c) State what could happen if the live and neutral wires were swapped in the plug.

A bathroom user switches on a mains-powered radio with wet hands. (a) Explain the hazard. (b) State two precautions that reduce it. (c) Explain why a double-insulated shaver with no earth wire is the safer design for bathrooms.