Domestic electricity and safetyIB MYP Physics: Subtopic test

1. 1
   A family in Abu Dhabi buys an electric kettle with a metal casing. The kettle has a three-pin plug fitted with a fuse and is connected to the mains supply.

   (a)

   Which wire in the kettle's cable is the live wire, and what colour is its insulation?

   [1 mark]

   • ABlue
   • BGreen and yellow
   • CBrown
   • DBlack

   (b)

   The mains supply is alternating current (a.c.). Which statement describes it?

   [1 mark]

   • AThe current repeatedly reverses direction, completing 50 cycles each second
   • BThe current always flows in one direction at a steady value
   • CThe current flows in one direction but its size changes 50 times each second
   • DThe current reverses direction only when the kettle is switched off

   (c)

   Explain why the metal casing of the kettle is connected to the earth wire.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hair salon in Dubai uses a hairdryer that normally draws a current of 8 A from the 230 V mains supply. The plug can be fitted with a 1 A, 3 A, 5 A or 13 A fuse.

   (a)

   Which fuse is the most suitable for the hairdryer's plug?

   [1 mark]

   • A1 A
   • B3 A
   • C5 A
   • D13 A

   (b)

   In which wire of the plug should the fuse be placed?

   [1 mark]

   • AThe neutral wire
   • BThe live wire
   • CThe earth wire
   • DThe outer casing of the cable

   (c)

   Explain how a fuse protects the hairdryer circuit.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A school workshop in Singapore has a power drill with a plastic casing and a two-core cable with no earth wire. The workshop's consumer unit (fuse board) uses circuit breakers instead of fuses.

   (a)

   Explain how double insulation protects the user of the drill even though it has no earth wire.

   [3 marks]

   (b)

   Describe how a circuit breaker protects a circuit and give two advantages it has over a fuse.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science club in a village school has an unreliable mains supply. The club plans to investigate fuse wires to learn about electrical safety. The school is also deciding whether to power its classroom lamps from the mains supply or from d.c. cells charged by solar panels.

   (a)

   The club hypothesises that the thickness of a fuse wire affects the current at which it melts. State a testable hypothesis with a scientific reason, identify the independent, dependent and one control variable, and outline a safe method to test it.

   [6 marks]

   (b)

   Discuss and evaluate whether the school should power its classroom lamps from the mains supply or from d.c. cells charged by solar panels.

   [6 marks]

   Total for question 4: 12 marks

End of questions