1. 1
   An old toaster's mains cable has become frayed with age, exposing bare copper wire beneath the damaged plastic insulation, and a family must decide what to do before using it again.

   (a)

   An old toaster's mains cable has become frayed, exposing the bare copper wire beneath the plastic insulation. What hazard does this damaged insulation create?

   [1 mark]

   • AIt increases the risk of electric shock if the exposed wire is touched
   • BIt automatically switches the toaster off for safety
   • CIt reduces the current flowing to the heating element
   • DIt has no effect on safety, only on appearance

   (b)

   The family also notices the toaster's cable feels warm even during normal use, more than they would expect. What could cause a cable to overheat like this during normal use?

   [1 mark]

   • AThe cable has no current flowing through it at all
   • BThe cable is earthed correctly
   • CThe cable is connected to a fuse of the correct rating
   • DThe cable is carrying a current greater than it is rated to carry safely

   (c)

   State two other hazards, besides damaged insulation and overheating cables, that can make it dangerous to use a mains electrical appliance such as this toaster.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a small workshop, several power tools are plugged into a single extension lead connected to one wall socket, and the workshop owner notices the extension lead becomes noticeably hot during use.

   (a)

   What is the most likely explanation for this?

   [1 mark]

   • AThe wall socket is providing too low a voltage
   • BThe extension lead has too much resistance to allow any current to flow
   • CThe extension lead is overloaded, drawing a total current greater than it is rated to carry
   • DThe power tools are all switched off

   (b)

   The workshop's wiring includes a fuse in the plug of each power tool. What is the purpose of the fuse?

   [1 mark]

   • ATo increase the current supplied to the tool
   • BTo break the circuit if the current becomes too large, protecting the cable and appliance
   • CTo convert the mains a.c. supply into d.c.
   • DTo store electrical energy for use during a power cut

   (c)

   Explain how the workshop owner should choose an appropriate fuse rating for a power tool, and explain what could happen if a fuse with too high a rating were fitted instead.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An electrician explains to an apprentice how a standard mains electrical circuit is wired, using a live wire, a neutral wire and an earth wire, and why the switch must always be placed in a particular position.

   (a)

   An electrician explains to an apprentice that a standard mains circuit consists of a live wire, a neutral wire and an earth wire. Describe the role of the live wire and the neutral wire in a normal working mains circuit.

   [3 marks]

   (b)

   Explain why the switch controlling an appliance must always be connected in the live wire, rather than the neutral wire, for the circuit to be switched off safely.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An appliance manufacturer produces two types of appliance: a hairdryer, which has an all-plastic outer casing and no earth wire in its cable, and a washing machine, which has a metal outer casing connected to an earth wire, and a safety inspector reviews both designs.

   (a)

   Explain, using the ideas of double insulation and earthing, why each design is considered electrically safe, and explain why a metal-cased appliance without an earth wire connected to it would be dangerous.

   [6 marks]

   (b)

   The safety inspector notices that the washing machine's plug contains a fuse as well as an earth wire, and asks the manufacturer to explain why a double-insulated appliance, such as the hairdryer, still needs a fuse even though it has no earth wire at all. Explain the separate roles played by the fuse and the earth wire in protecting against different types of electrical fault, and explain why a fuse alone is considered sufficient for a double-insulated appliance.

   [6 marks]

   Total for question 4: 12 marks

End of questions