OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Explain how solenoid arrangements can enhance the magnetic effect
Full specification wording
Magnets and magnetic fields: explain how solenoid arrangements can enhance the magnetic effect
A single straight wire carrying a current creates a weak circular magnetic field around it.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 7 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A single straight wire carrying a current creates a weak circular magnetic field around it. Winding the wire into a coil, a solenoid, concentrates many turns so each turn's field adds to its neighbours' inside the coil, producing a much stronger, more uniform field along the axis. Adding an iron core magnetises the iron and strengthens the field further, making an electromagnet. Increasing the current or the number of turns per unit length also strengthens the effect. The field outside resembles a bar magnet's, with a north pole at one end and a south pole at the other. Learners should explain enhancement by reference to combining turns, adding a core and increasing current, not merely state that a solenoid is magnetic.
What earns the marks
- Identifies that winding the wire into a coil concentrates many turns so their individual fields combine and reinforce inside the coil.
- Explains that inserting an iron core becomes magnetised and strengthens the magnetic field, forming an electromagnet.
- States that increasing the current or the number of turns increases the strength of the magnetic effect.
- Describes the field pattern of a solenoid as similar to a bar magnet, with a north pole at one end and a south pole at the other.
Common mistakes and how to put them right
Claims a solenoid has no field outside the coil.
Put it right by noting the external field resembles a bar magnet's.
Asserts that adding a core weakens the field.
Put it right by explaining the iron core becomes magnetised and strengthens it.
Believes more turns reduce the effect.
Put it right by stating that more turns per unit length increase the field strength.
Exam tips
- Read the question for the word explain, then give a reason for each enhancement rather than listing features.
- Link each enhancement to how the individual magnetic fields combine or reinforce.
- Check whether the option or answer mentions the iron core, current and number of turns, since all can enhance the effect.
Try the lesson
The start of the Magnets and magnetic fields: explain how solenoid arrangements can enhance the magnetic effect lesson, made from checked teaching notes for this specification point.
Have a go first
A solenoid is made by winding wire into many loops around a tube. What is the main reason the field inside the tube is stronger than the field around a single loop of the same wire?
Listen
A single straight wire carrying a current creates a weak circular magnetic field around it. Winding the wire into a coil, a solenoid, concentrates many turns so each turn's field adds to its neighbours' inside the coil, producing a much stronger, more uniform field along the axis. Adding an iron core magnetises the iron and strengthens the field further, making an electromagnet. Increasing the current or the number of turns per unit length also strengthens the effect. The field outside resembles a bar magnet's, with a north pole at one end and a south pole at the other. Learners should explain enhancement by reference to combining turns, adding a core and increasing current, not merely state that a solenoid is magnetic. A strong answer earns marks for these points. Identifies that winding the wire into a coil concentrates many turns so their individual fields combine and reinforce inside the coil. Explains that inserting an iron core becomes magnetised and strengthens the magnetic field, forming an electromagnet. States that increasing the current or the number of turns increases the strength of the magnetic effect. Describes the field pattern of a solenoid as similar to a bar magnet, with a north pole at one end and a south pole at the other. A common slip: Claims a solenoid has no field outside the coil. Instead, noting the external field resembles a bar magnet's. Exam tip: Read the question for the word explain, then give a reason for each enhancement rather than listing features.
Key words
Say what each word means before you turn the card.
Combining fields of multiple turns
Try answering aloud or in your head before turning the card.
Iron core and electromagnets
Try answering aloud or in your head before turning the card.
Field pattern of a solenoid
Try answering aloud or in your head before turning the card.
See every definition
- Combining fields of multiple turns
- Winding the wire into a coil concentrates many turns so each turn's field adds to its neighbours' inside the coil, producing a much stronger, more uniform field along the axis.
- Iron core and electromagnets
- Adding an iron core magnetises the iron and strengthens the field further, making an electromagnet.
- Field pattern of a solenoid
- The field outside resembles a bar magnet's, with a north pole at one end and a south pole at the other.
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