OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Describe the characteristics of the magnetic field of a magnet, showing…
Full specification wording
Magnets and magnetic fields: describe the characteristics of the magnetic field of a magnet, showing how strength and direction change from one point to another (to include: diagrams to show how the strength of the field varies around them and ways of investigating this)
A magnetic field is the region around a magnet where a magnetic force acts on another magnet or on a magnetic material.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 3 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A magnetic field is the region around a magnet where a magnetic force acts on another magnet or on a magnetic material. Field lines show direction: by convention they run from the north pole round to the south pole outside the magnet, and the arrow on a line gives the force direction on a north pole placed at that point. Field lines show strength through spacing: lines drawn close together mark a strong field, widely spaced lines mark a weak field. Around a bar magnet the lines crowd near the poles and spread out further away, so the field is strongest at the poles and weakest at the sides and at distance. Diagrams use arrows and line spacing to convey both direction and strength. Investigation methods include plotting with a small plotting compass moved around the magnet, and sprinkling iron filings to reveal the pattern.
What earns the marks
- States that field lines run from the north pole to the south pole outside the magnet.
- Explains that closely spaced field lines indicate a stronger field and widely spaced lines a weaker field.
- Identifies that the field of a bar magnet is strongest at its poles and weaker further away.
- Describes plotting the field with a small compass or iron filings to show direction and pattern.
Common mistakes and how to put them right
Draws field lines running from south to north outside the magnet.
Put it right: Reverse them to run from north to south outside.
Treats evenly spaced lines as showing a stronger field.
Put it right: Use closer spacing to show greater strength.
Places the strongest field at the middle of a bar magnet.
Put it right: Locate it at the poles instead.
Exam tips
- Read the question for whether it asks about direction, strength or both, and answer each part.
- Use the spacing of lines, not their length, as the evidence for field strength.
- When describing an investigation, name the apparatus (plotting compass or iron filings) and what it reveals.
Try the lesson
The start of the Magnets and magnetic fields: describe the characteristics of the magnetic field of a magnet, showing how strength and direction change from one point to another (to include: diagrams to show how the strength of the field varies around them and ways of investigating this) lesson, made from checked teaching notes for this specification point.
Have a go first
On a field-line diagram of a bar magnet, what does the spacing of the field lines tell you about the magnetic field?
Listen
A magnetic field is the region around a magnet where a magnetic force acts on another magnet or on a magnetic material. Field lines show direction: by convention they run from the north pole round to the south pole outside the magnet, and the arrow on a line gives the force direction on a north pole placed at that point. Field lines show strength through spacing: lines drawn close together mark a strong field, widely spaced lines mark a weak field. Around a bar magnet the lines crowd near the poles and spread out further away, so the field is strongest at the poles and weakest at the sides and at distance. Diagrams use arrows and line spacing to convey both direction and strength. Investigation methods include plotting with a small plotting compass moved around the magnet, and sprinkling iron filings to reveal the pattern. A strong answer earns marks for these points. States that field lines run from the north pole to the south pole outside the magnet. Explains that closely spaced field lines indicate a stronger field and widely spaced lines a weaker field. Identifies that the field of a bar magnet is strongest at its poles and weaker further away. Describes plotting the field with a small compass or iron filings to show direction and pattern. Exam tip: Read the question for whether it asks about direction, strength or both, and answer each part.
Key words
Say what each word means before you turn the card.
Magnetic field direction
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Field strength and line spacing
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Field around a bar magnet
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Investigating fields with compasses and iron filings
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See every definition
- Magnetic field direction
- By convention the lines run from the north pole round to the south pole outside the magnet, and the arrow gives the force direction on a north pole placed at that point.
- Field strength and line spacing
- Lines drawn close together mark a strong field, while widely spaced lines mark a weak field.
- Field around a bar magnet
- The lines crowd near the poles and spread out further away, so the field is strongest at the poles and weakest at the sides and at distance.
- Investigating fields with compasses and iron filings
- Methods include plotting with a small plotting compass moved around the magnet, and sprinkling iron filings to reveal the pattern.
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