AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The magnetic field around a solenoid has a similar shape to that of a bar…
Full specification wording
Electromagnetism: The magnetic field around a solenoid has a similar shape to that of a bar magnet. Adding an iron core increases the strength of the magnetic field of a solenoid. An electromagnet is a solenoid with an iron core.
A solenoid is a long coil of insulated wire.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A solenoid is a long coil of insulated wire. When current flows, each turn produces a field; inside the coil these fields combine into a strong, uniform field along the axis, while outside the pattern resembles the field of a bar magnet, with field lines emerging from one end and entering the other. The end from which field lines emerge acts as a north pole. Reversing the current reverses the poles. Inserting a soft iron core concentrates and strengthens the field because iron is easily magnetised, so the solenoid becomes an electromagnet. Unlike a permanent bar magnet, an electromagnet can be switched on and off and its strength changed by altering current or number of turns.
What earns the marks
- A solenoid is a coil of insulated wire carrying a current; its field is produced only while current flows.
- Inside the solenoid the field is strong and approximately uniform along the axis; outside it resembles the field around a bar magnet.
- Field lines emerge from the north-seeking end and enter the south-seeking end; reversing current reverses the poles.
- Adding a soft iron core increases field strength because the iron becomes magnetised and adds to the field.
- An electromagnet is a solenoid with an iron core, giving a magnetic field that can be switched on and off.
- Increasing current or the number of turns per unit length increases the strength of the solenoid's field.
Common mistakes and how to put them right
Thinking the field exists only inside the solenoid.
Put it right by describing the external field pattern, which resembles a bar magnet's field.
Believing any metal core strengthens the field.
Put it right by specifying soft iron, which is easily magnetised; materials such as copper or aluminium do not have this effect.
Confusing the direction of field lines with the direction of current.
Put it right by using the right-hand grip rule to relate current direction to the field and pole positions.
Exam tips
- Sketch the field with arrows from north to south outside the coil and label the poles before writing your explanation.
- When asked why an iron core helps, link it to the core becoming an induced magnet that adds to the coil's field.
- Compare an electromagnet with a permanent bar magnet in terms of switching and strength control to gain comparison marks.
Try the lesson
The start of the Electromagnetism: The magnetic field around a solenoid has a similar shape to that of a bar magnet. Adding an iron core increases the strength of the magnetic field of a solenoid. An electromagnet is a solenoid with an iron core. lesson, made from checked teaching notes for this specification point.
Have a go first
Which object has a magnetic field with the same shape as the field around a solenoid?
Listen
A solenoid is a long coil of insulated wire. When current flows, each turn produces a field; inside the coil these fields combine into a strong, uniform field along the axis, while outside the pattern resembles the field of a bar magnet, with field lines emerging from one end and entering the other. The end from which field lines emerge acts as a north pole. Reversing the current reverses the poles. Inserting a soft iron core concentrates and strengthens the field because iron is easily magnetised, so the solenoid becomes an electromagnet. Unlike a permanent bar magnet, an electromagnet can be switched on and off and its strength changed by altering current or number of turns. A strong answer earns marks for these points. A solenoid is a coil of insulated wire carrying a current; its field is produced only while current flows. Inside the solenoid the field is strong and approximately uniform along the axis; outside it resembles the field around a bar magnet. Field lines emerge from the north-seeking end and enter the south-seeking end; reversing current reverses the poles. Adding a soft iron core increases field strength because the iron becomes magnetised and adds to the field. A common slip: Thinking the field exists only inside the solenoid. Instead, describing the external field pattern, which resembles a bar magnet's field. Exam tip: Sketch the field with arrows from north to south outside the coil and label the poles before writing your explanation.
Key words
Say what each word means before you turn the card.
Solenoid
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Electromagnet
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Soft iron core
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Field shape and polarity
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See every definition
- Solenoid
- A long coil of insulated wire carrying a current, whose field is produced only while current flows.
- Electromagnet
- A solenoid with an iron core, giving a magnetic field that can be switched on and off.
- Soft iron core
- A core that increases field strength because the iron becomes magnetised and adds to the field.
- Field shape and polarity
- Inside the field is strong and approximately uniform along the axis; outside it resembles the field around a bar magnet, with field lines emerging from the north-seeking end.
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