Transformers and the National GridIB MYP Physics: Flashcards

What these 13 flashcards ask

What are the three main parts of a transformer?
Why must a transformer use alternating current?
State the turns ratio equation.
How does a step-up transformer differ from a step-down transformer?
What is the equation for an ideal transformer?
A transformer raises the voltage by a factor of 10. What happens to the current (ideal)?
What is the job of the soft iron core?
Give the equation for power lost as heat in a cable.
Why is electricity transmitted at high voltage?
Why does halving the current cut the heat loss to a quarter?
Where does a step-up transformer sit in the National Grid?
Why are step-down transformers used near homes?
What is an ideal transformer?

Exam questions on Transformers and the National Grid

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
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
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

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).