TransformersAQA A-Level Physics: Mind map

Exam questions on Transformers

1. A mobile phone charger contains a step-down transformer. The primary coil has 2300 turns and is connected to the 230 V alternating mains supply. The secondary coil supplies the phone with a potential difference of 5.0 V.
   The core of the transformer is made from thin sheets of iron, insulated from each other, rather than from a single solid block of iron. Explain why this reduces the energy wasted in the core.2 marks
2. A technician is testing a laboratory transformer that has 120 turns on its primary coil and 600 turns on its secondary coil. The primary coil is connected to a 12 V alternating supply and a lamp is connected across the secondary coil.
   A voltmeter connected across the lamp reads 54 V rather than the value expected from the turns ratio. Suggest two reasons why the secondary p.d. is lower than the ideal value.2 marks
3. A power station generates 50 MW of electrical power. The power is sent to a town through transmission lines of total resistance 8.0 Ω. The power station can either send the power directly at 25 kV or use a step-up transformer to send it at 400 kV.
   Calculate the power wasted in the lines if the power is sent directly at 25 kV.3 marks