Predict field changes when current direction reverses
Compare wire circulation and solenoid poles using explicit view and conventional-current conventions.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Use the wire grip rule and solenoid face rule.
- Distinguish physical direction from viewing convention.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Outward current gives anticlockwise wire field. What does inward current give?
What you will learn
- Compare wire circulation and solenoid poles using explicit view and conventional-current conventions.
- Separate physical current reversal from magnitude and observer changes before reversing field arrows or pole labels.
A single current reversal reverses field direction
For a fixed straight-wire geometry, reversing conventional current reverses the circular field arrow sense. Outward page current gives anticlockwise circulation; inward current gives clockwise circulation. At the right-hand reference point the corresponding directions are upward and downward.
For a fixed solenoid winding, reversing current exchanges north and south ends and reverses internal and external arrows. A right face that had anticlockwise current and was north becomes clockwise and south when current reverses. Keep the same viewing side throughout the comparison.
Do not confuse reversal and other changes
If current magnitude stays the same, the isolated coil or wire field strength at the same point is unchanged in the simple model, though its direction reverses. If magnitude also changes, direction and strength must be considered separately. A changed core or coil geometry is an additional condition.
Changing the observer’s viewing side reverses apparent clockwise sense without physically reversing current. Reorienting a compass or redrawing a diagram likewise does not itself change the field. Judge physical changes from the stated current, winding, geometry and view rather than from page appearance alone.
Sources for this lesson
Pause and explain
An observer walks to the opposite end of an unchanged solenoid. Does apparent clockwise reversal prove current physically reversed?
Worked example
A fixed solenoid right face changes from anticlockwise to clockwise current, seen from the same right-end view. What happens?
Show the worked solution
- The original right face is north.
- Reversed current makes it south.
- The left face and all field arrows exchange accordingly.
Answer Right N becomes S; left S becomes N; field direction reverses.
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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.
For a fixed page-normal wire, compare outward and inward current at equal magnitudes.
Give me a hint
Use the same page view and reference point.
Compare my reasoning
- Outward gives anticlockwise arrows.
- Inward gives clockwise arrows.
- At the right point the field changes from up to down.
Circulation reverses; right-point direction changes up to down; model strength is unchanged.
Look for these in your work
- Keep magnitude fixed.
- State local direction as well as circulation.
A fixed solenoid has right N and left S. Reverse current alone and state poles and central field.
Give me a hint
Exchange poles while retaining winding and view.
Compare my reasoning
- Right becomes S.
- Left becomes N.
- Central internal S→N now points leftward.
Right S, left N; central field leftward.
Look for these in your work
- Keep the physical ends fixed.
- Reverse the internal arrows.
A comparison changes current magnitude and viewing side, then uses apparent clockwise sense to claim the physical field reversed. Explain why more information is needed.
Give me a hint
Separate physical current direction from observer convention.
Compare my reasoning
- Magnitude change affects strength.
- A view change can reverse apparent sense.
- Physical reversal requires the current-direction information for the same winding.
Apparent sense alone under a changed view does not establish physical field reversal.
Look for these in your work
- Identify both changes.
- Request a consistent current/view convention.
Common mistakes
- Keep the viewing side fixed.
- Magnitude and sign are separate.
- Observer reversal is not current reversal.
What can you explain now?
At fixed geometry, what does reversing current alone do?
Compare with the explanation
Reverses magnetic-field direction
The direction follows current sign; unchanged magnitude retains the isolated model’s strength.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Separate physical current reversal from magnitude and observer changes before reversing field arrows or pole labels.
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.