Induction, generators and transformers Edexcel International GCSE Science (Double Award) revision
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In plain words
Move a magnet near a coil of wire and you make a voltage in the coil, as long as something is changing. No movement, no voltage. That is how generators make electricity. A transformer uses the same trick to change the size of an alternating voltage: more turns on the output coil gives a bigger voltage.
Three things to know
- A voltage is induced in a conductor when it cuts magnetic field lines, or when the field through a coil changes. Moving faster, a stronger magnet or more turns give a bigger voltage.
- A generator spins a coil in a magnetic field (or a magnet in a coil) to produce alternating current.
- A transformer changes the size of an alternating voltage: Vp ÷ Vs = Np ÷ Ns. Electricity is transmitted at high voltage so that the current is small and less energy is wasted heating the cables.
Worked example
A transformer has 400 turns on the primary coil and 100 on the secondary. The input is 240 V. Find the output.
- Vs ÷ Vp = Ns ÷ Np, so Vs = 240 × 100 ÷ 400.
- = 60 V.
Tips and tricks
- Sense-check a transformer: fewer turns on the secondary must give a smaller voltage.
- Transformers only work with alternating current. A steady current gives a steady field, and a steady field induces nothing.
It lands in your notebook with its questions as flashcards.
Induction, generators and transformers: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
A magnet is held still inside a coil. What voltage is induced?
The field through the coil must be changing for a voltage to be induced.
Which change increases the voltage from a generator?
More turns cut more field lines each second.
A transformer has 100 primary turns and 500 secondary turns. The input is 20 V. What is the output?
The voltage is stepped up in the same ratio as the turns: × 5.
Why is a transformer's core made of iron?
No current flows through the core; it links the magnetic field.
Why is mains electricity transmitted at high voltage?
A high voltage means a low current, and heating depends on the current.
What kind of current does a simple generator with slip rings produce?
The induced voltage changes direction every half turn.
Quiz
6 questions
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Worksheet
4 questions, 11 marks. Write your answers on paper, then check them.
Induction, generators and transformers
Edexcel International GCSE Science (Double Award) 4SD0 · 11 marks · papermunch.org
Name ______________________________ Date ______________
State three ways of increasing the voltage induced when a magnet is pushed into a coil.[3]
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Move the magnet faster, use a stronger magnet, and use a coil with more turns.
A transformer has 200 turns on its primary coil and 50 turns on its secondary. The primary voltage is 240 V. Calculate the secondary voltage.[3]
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60 V. Vs = 240 × 50 ÷ 200.
Explain why a transformer does not work with direct current.[2]
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A steady current gives a steady magnetic field; a voltage is only induced in the secondary when the field is changing.
Explain why electricity is transmitted across the country at very high voltages.[3]
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For the same power, a high voltage means a small current, so much less energy is wasted as heat in the cables.
Answers: Induction, generators and transformers
- 1. Move the magnet faster, use a stronger magnet, and use a coil with more turns.
- 2. 60 V. Vs = 240 × 50 ÷ 200.
- 3. A steady current gives a steady magnetic field; a voltage is only induced in the secondary when the field is changing.
- 4. For the same power, a high voltage means a small current, so much less energy is wasted as heat in the cables.