TransformersAQA A-Level Physics: Flashcards

What these 12 flashcards ask

State the transformer equation.
What is the efficiency of a transformer?
Why does a transformer need alternating current?
What is a step-up transformer?
What are eddy currents?
How are eddy currents reduced?
Name four causes of energy loss in a transformer.
How can flux leakage be reduced?
Why is electricity transmitted at high voltage?
What is the formula for power loss in a transmission line?
By what factor does power loss fall if the transmission voltage is increased 10 times?
Why must the core of a transformer be made of soft iron?

Exam questions on Transformers

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
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
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

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).