Transformers and the National GridIB MYP Physics: Mind map

Exam questions on Transformers and the National Grid

1. A company in Shenzhen designs a phone charger that contains a transformer. The charger is plugged into a 230 V alternating mains supply and must deliver 5 V to the phone. The primary coil of the transformer has 1150 turns.
   Calculate the number of turns on the secondary coil of the charger. Assume the transformer is ideal.2 marks
2. A student in Lagos builds a model transformer from two coils of insulated wire wound on a soft iron core. She connects the primary coil to a low-voltage alternating supply and a lamp to the secondary coil, and the lamp lights. She then replaces the alternating supply with a battery: the lamp flashes briefly when she connects it, then stays off.
   Explain why the lamp lights continuously when the primary coil is connected to an alternating supply.2 marks
3. A power station in Poland generates electricity at 25 kV. Transformers raise this to 400 kV for transmission through overhead cables to a city, where further transformers reduce it in stages to 230 V for homes. The transmission cables have a total resistance of 20 Ω.
   Outline how transformers are used to carry electricity from the power station to homes.3 marks