Electrical power and safetyIB MYP Sciences: Subtopic test

1. 1
   A family in Dubai uses an electric kettle rated at 2.0 kW. The kettle works from the 230 V mains supply.

   (a)

   Calculate the current in the kettle when it is working normally.

   [1 mark]

   • A0.12 A
   • B460 000 A
   • C8.7 A
   • D2.0 A

   (b)

   The kettle is switched on for 3.0 minutes. How much energy does it transfer?

   [1 mark]

   • A6000 J
   • B360 000 J
   • C11 J
   • D2000 J

   (c)

   Calculate the energy transferred by the kettle in 3.0 minutes, in kilowatt-hours.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A household in Auckland pays 30 cents for each kilowatt-hour (kWh) of electricity. A 1.5 kW electric heater runs for 4.0 hours each evening.

   (a)

   Which quantity is measured in kilowatt-hours?

   [1 mark]

   • APower
   • BCurrent
   • CPotential difference
   • DEnergy

   (b)

   How much energy does the heater transfer in one evening?

   [1 mark]

   • A6.0 kWh
   • B0.38 kWh
   • C5.5 kWh
   • D6.0 kW

   (c)

   Calculate the cost of running the heater for one evening.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A washing machine in a home in Cairo is connected to the mains supply by a three-pin plug that contains a fuse. The machine has a metal case and is rated at 2300 W on the 230 V mains.

   (a)

   Explain how the earth wire and the fuse together protect a user if a fault makes the live wire touch the metal case.

   [3 marks]

   (b)

   The plug can be fitted with a 3 A, 5 A or 13 A fuse. Calculate the normal current in the washing machine and decide which fuse to fit, giving a reason.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The science club at a school in Manila is investigating how to cut the school's electricity bill. Each classroom lamp is on for 8.0 hours a day for 30 days. The club compares three lamps that give about the same brightness: a 60 W filament lamp, a 14 W compact fluorescent lamp (CFL) and a 9 W LED lamp. Electricity costs 25 cents per kilowatt-hour.

   (a)

   Calculate the energy transferred and the cost for each lamp over the 30 days, describe the pattern in the results and evaluate how useful these figures are for choosing a lamp.

   [6 marks]

   (b)

   Discuss the economic, environmental and social implications of replacing all of the school's filament lamps with LED lamps, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions