1. 1
   A toy manufacturer includes a small transformer in a battery charger to reduce the mains potential difference to a safer, lower value for charging a toy's battery. The transformer has a primary coil and a secondary coil wound on the same iron core.

   (a)

   Which type of transformer is this?

   [1 mark]

   • AA step-down transformer
   • BA step-up transformer
   • CAn isolating transformer with equal coils
   • DA rectifying transformer

   (b)

   Which of the following is a requirement for this transformer to work, regarding the type of supply connected to the primary coil?

   [1 mark]

   • AThe primary coil must be connected to a direct current supply
   • BThe primary coil must be connected to an alternating current supply
   • CThe primary coil must be connected to a constant static charge
   • DThe type of supply makes no difference to how a transformer works

   (c)

   Explain how a changing current in the primary coil of the transformer results in a potential difference being induced across the secondary coil.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   At a rural substation, a step-up transformer increases the potential difference of electricity generated at a power station before it is sent along the National Grid's overhead cables.

   (a)

   Compared with the number of turns on its primary coil, the secondary coil of this transformer must have:

   [1 mark]

   • AExactly the same number of turns as the primary coil
   • BFewer turns than the primary coil
   • CMore turns than the primary coil
   • DNo turns, since step-up transformers have no secondary coil

   (b)

   Assuming the transformer is 100% efficient, what happens to the current in the National Grid cables as a result of the potential difference being stepped up?

   [1 mark]

   • AThe current becomes direct current instead of alternating current
   • BThe current increases
   • CThe current stays exactly the same
   • DThe current decreases

   (c)

   Explain why transmitting electrical power through the National Grid at a high potential difference (and correspondingly low current) reduces the amount of energy wasted in the overhead cables.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A step-down transformer at a factory has 2000 turns on its primary coil and 100 turns on its secondary coil. The primary coil is connected to a 230 V alternating supply.

   (a)

   Calculate the potential difference produced across the secondary coil.

   [3 marks]

   (b)

   The secondary coil of this transformer supplies a current of 8.0 A to a factory machine. Assuming the transformer is 100% efficient, calculate the current drawn from the 230 V primary supply, and calculate the power supplied to the machine.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Before the National Grid used high-voltage transmission, early electricity supply networks in the late 19th century transmitted power at relatively low potential differences over local distances, which limited how far electricity could be economically distributed.

   (a)

   Explain, using the roles of step-up and step-down transformers, how the modern National Grid transmits electrical power efficiently from power stations to homes and businesses over long distances.

   [6 marks]

   (b)

   A historian researching this early period notes that some engineers argued for using direct current at low potential difference throughout the entire network, rather than the alternating current, transformer-based system that eventually became standard. Evaluate why a system based on alternating current and transformers was better suited to a national electricity grid than one based on direct current transmitted at a single, low potential difference throughout.

   [6 marks]

   Total for question 4: 12 marks

End of questions