AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Transformers (HT only): Iron is used as it is easily magnetised.
Iron is chosen for transformer cores because it magnetises and demagnetises easily, allowing its magnetism to follow an alternating magnetic field that changes direction rapidly.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 3
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Iron is chosen for transformer cores because it magnetises and demagnetises easily, allowing its magnetism to follow an alternating magnetic field that changes direction rapidly. Each time the primary alternating current changes, the magnetic field in the core changes with it. It is this changing magnetic field in the core that induces an alternating potential difference in the secondary coil. A magnetically hard material like steel would not be suitable because, once magnetised, it tends to stay magnetised. The magnetic field in the core would not continuously change with the primary current, preventing the induction of the output.
What earns the marks
- Iron is used for the core because it is easily magnetised and demagnetised.
- The primary coil produces an alternating magnetic field.
- The iron core carries this changing magnetic field to the secondary coil.
- A changing magnetic field is required to induce a potential difference in the secondary coil.
Common mistakes and how to put them right
Stating that iron is a good electrical conductor, which is relevant for the coils but not the core.
Suggesting that steel is used, forgetting that steel is magnetically hard and stays magnetised.
Saying iron is used because it is cheap or strong, rather than focusing on its magnetic properties.
Exam tips
- Always link the choice of iron to its ability to be easily magnetised and demagnetised.
- Avoid using the word 'steel' when describing transformer cores, as its magnetic properties are unsuitable.
Try the lesson
The start of the Transformers (HT only): Iron is used as it is easily magnetised. lesson, made from checked teaching notes for this specification point.
Have a go first
Why is iron used for the core of a transformer?
Listen
Iron is chosen for transformer cores because it magnetises and demagnetises easily, allowing its magnetism to follow an alternating magnetic field that changes direction rapidly. Each time the primary alternating current changes, the magnetic field in the core changes with it. It is this changing magnetic field in the core that induces an alternating potential difference in the secondary coil. A magnetically hard material like steel would not be suitable because, once magnetised, it tends to stay magnetised. The magnetic field in the core would not continuously change with the primary current, preventing the induction of the output. A strong answer earns marks for these points. Iron is used for the core because it is easily magnetised and demagnetised. The primary coil produces an alternating magnetic field. The iron core carries this changing magnetic field to the secondary coil. A changing magnetic field is required to induce a potential difference in the secondary coil. Exam tip: Always link the choice of iron to its ability to be easily magnetised and demagnetised.
Key words
Say what each word means before you turn the card.
Iron core
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Easily magnetised
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Changing magnetic field
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See every definition
- Iron core
- Iron is used for the core because it is easily magnetised and demagnetised, allowing its magnetism to follow an alternating magnetic field.
- Easily magnetised
- Iron is used as it is easily magnetised, so its magnetism can follow a magnetic field that changes direction rapidly.
- Changing magnetic field
- This is required in the core to induce a potential difference in the secondary coil.
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