Compare relative magnetic field strength from line spacing
Use a consistent drawing convention to identify stronger and weaker regions without inventing a numerical scale.
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Read a field-line pattern.
- Distinguish a qualitative comparison from a measurement.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a field-line arrow identify?
What you will learn
- Interpret closer field-line spacing as stronger relative field.
- State the drawing conditions needed for a fair comparison.
Read the density of representative lines
On a consistently drawn magnetic-field diagram, closer spacing of field lines represents a stronger field and wider spacing a weaker field. Around a bar magnet the external field is strongest near the poles in the usual schematic pattern. Compare line spacing at the locations actually named.
The arrows show direction; the spacing represents relative strength. Long arrows or dark ink do not automatically represent greater field strength. A point with the same arrow direction can have a different strength from another point with wider or narrower spacing.
Keep the representation consistent
Compare regions in the same diagram or diagrams using the same line-density convention and spatial scale. If an illustrator simply draws twice as many representative lines in an otherwise unrelated picture, counting them does not prove the physical magnet became stronger.
A qualitative diagram usually gives no numerical field calibration. 'More closely spaced' supports a stronger-versus-weaker conclusion, but it does not by itself give a field value or exact ratio. Use supplied quantitative measurements only when the question provides them.
Sources for this lesson
Pause and explain
Lines at A are wider apart than at B in one consistent map. Which region is stronger?
Worked example
In one consistently drawn map, lines are closer at P than Q. Compare the field strengths.
Show the worked solution
- The same mapping convention is used.
- P has closer line spacing.
- Closer spacing represents a stronger field.
Answer The field is stronger at P than at Q; no numerical ratio is established.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare P and Q when P has closer field lines in the same map.
Give me a hint
Use line spacing under the stated common convention.
Compare my reasoning
- The convention is consistent.
- P's lines are closer.
- P therefore represents the stronger field.
P has the stronger relative field.
Look for these in your work
- Refer to spacing.
- Keep the comparison qualitative.
Explain why stronger regions near a bar magnet's poles are shown with closer lines.
Give me a hint
Connect the drawn density to the represented field property.
Compare my reasoning
- Line spacing represents relative strength.
- The usual external pattern is stronger near the poles.
- Closer representative lines convey that stronger region.
Closer spacing represents the stronger near-pole field.
Look for these in your work
- State the convention.
- Avoid treating the lines as physical material.
Two independent pictures use different scales and line counts. Can counting lines alone establish an exact strength ratio?
Give me a hint
Check whether the representation has a common calibration.
Compare my reasoning
- The scales and line-density choices differ.
- Counts are not a shared physical measurement.
- No exact ratio is established without appropriate calibration.
No; a consistent scale and calibrated convention would be needed.
Look for these in your work
- Identify the mismatch.
- Do not invent a ratio from ink counts.
Common mistakes
- Spacing and arrow direction convey different information.
- Match drawing scales and conventions.
- Do not invent a strength ratio.
What can you explain now?
What does closer field-line spacing represent in a consistent diagram?
Compare with the explanation
A stronger relative field.
The line-density convention represents relative strength rather than literal threads.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Compare relative field strength from spacing with explicit representation limits.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.