Determine magnetic field direction using a north pole
Use the north-seeking compass tip as a local direction indicator and distinguish it from the south end.
Section 4.1 · Simple phenomena of magnetism
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Follow the selected magnetism or charge section. Field lines are explanatory models, not material threads or measured force values. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall the external bar-magnet pattern.
- Identify the labelled north tip of a compass.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which pole is used in the magnetic-field direction definition?
What you will learn
- State the north-pole force definition of field direction.
- Read a compass needle tangent to a local field line.
Use the defined test-pole direction
The magnetic field direction at a point is the direction of the force on a north pole placed there. The south pole experiences the opposite force in the simple test-pole model. Always name the test pole; saying only 'a magnet points this way' leaves the convention ambiguous.
A small freely turning compass aligns with the local resultant field. Its north-seeking tip indicates the field direction along the tangent to a field line. The needle should not be drawn pointing toward the geographic top of every page irrespective of the nearby magnet.
Read the local position
Near the outside of a bar magnet's north end, the field points away from N. Near its south end, it points toward S. Above a bar labelled N left and S right, a suitable middle location has a field direction toward the right in the schematic pattern.
A real compass also responds to Earth's field and nearby magnetic objects. The ideal bar-magnet sketch assumes the stated magnet dominates. At a point where the ideal resultant field is zero, there is no uniquely defined direction from that zero field alone.
Pause and explain
A north compass tip points left. Which way is the local magnetic field?
Worked example
At a point the north tip of a small compass points east in the stated dominant field. Give the local field direction.
Show the worked solution
- The north tip indicates the defined direction.
- It points east.
- The local field direction is east.
Answer East; the force on a north test pole would be east.
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.
State the definition of magnetic field direction.
Give me a hint
Specify the pole whose force determines the direction.
Compare my reasoning
- Consider a magnetic test pole at the point.
- Use its north pole.
- The force direction on that north pole is the field direction.
The direction of force on a north pole at that point.
Look for these in your work
- Name north.
- Keep the location explicit.
A compass north tip points south-west. Give the field direction and the south-tip orientation.
Give me a hint
Read the named tip before reversing for the other end.
Compare my reasoning
- The field follows the north tip.
- It is south-west.
- The opposite south tip points north-east.
Field south-west; south tip north-east.
Look for these in your work
- Use the correct tip.
- Distinguish field and opposite end.
An ideal pair of fields cancels at one point. Does its field alone specify where a compass must point?
Give me a hint
A zero vector has no preferred direction.
Compare my reasoning
- The stated resultant is zero.
- Zero has no unique direction.
- Other real fields may still orient an actual compass.
No; the ideal zero field has no unique direction.
Look for these in your work
- Use the ideal condition.
- Separate other real influences.
Common mistakes
- Use the north tip.
- Read the local tangent, not the page orientation.
- A zero field has no unique direction.
What can you explain now?
Does the south tip define magnetic field direction?
Compare with the explanation
No.
The convention uses the force on a north pole; the south end points oppositely.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Use the north-pole convention and read local compass directions with the stated field conditions.
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.