Use the generator direction rule for motion field and current
Apply mutually perpendicular motion, field and induced conventional-current directions with explicit page conventions.
Extended only (Supplement); Physics 0625, 2026–2028. Use the stated source, operating conditions and meter ranges. Written practice is self-checked.
Before you begin
- Identify field and motion directions.
- Use into-page/out-of-page and conventional-current conventions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does a cross represent in a page-normal direction diagram?
What you will learn
- Apply mutually perpendicular motion, field and induced conventional-current directions with explicit page conventions.
- Use stated geometry and the generator right-hand convention, distinguishing imposed motion, reaction force and electron motion.
Set the three directions before using the rule
For the stated moving-conductor generator arrangement, Fleming’s right-hand rule relates imposed motion, magnetic field and induced conventional current: thumb follows motion, first finger follows field from north toward south, and second finger gives induced current. The external driving force maintains the imposed motion; it is not the same as the opposing magnetic reaction on the induced current.
Do not substitute the motor left-hand rule while keeping the thumb assigned to imposed generator motion. For a positively charged carrier the magnetic separation follows motion cross field; electrons move oppositely to conventional current. Page dots represent out of the page and crosses represent into the page.
Use a fully specified example
Take upward motion and rightward field, with the rod perpendicular to the page. The induced conventional current is into the page in a closed receiver. Reverse motion alone or field alone and it is out of the page. Reverse both and it is into the page again. The rod direction must allow the predicted along-rod current.
For rightward motion and a field into the page, induced conventional current is upward along a vertical rod. The current-produced magnetic force resists the imposed movement in the generating arrangement. A field and motion that are parallel give no corresponding ideal motional effect, so they cannot determine a non-zero third direction in this model.
Pause and explain
Upward motion/rightward field gives into-page current. Both motion and field reverse. What follows?
Worked example
A rod normal to the page moves upward through a rightward magnetic field. Find induced conventional-current direction in a closed receiver.
Show the worked solution
- Thumb follows upward motion.
- First finger follows rightward field.
- Second finger points into the page.
Answer Into the page, represented by a cross.
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.
For upward motion and rightward field with a page-normal rod, give induced conventional current and opposite electron motion.
Give me a hint
Use motion cross field, then reverse for electrons.
Compare my reasoning
- The induced conventional direction is into the page.
- Use a cross for that direction.
- Electron motion is out of the page.
Conventional current into page; electrons out of page.
Look for these in your work
- State the geometry.
- Separate both conventions.
A vertical rod moves rightward in a magnetic field into the page. Find induced conventional-current direction.
Give me a hint
Use thumb right, first finger into page and second finger for current.
Compare my reasoning
- Motion is rightward.
- Field is into the page.
- The current direction is upward along the rod.
Upward conventional current.
Look for these in your work
- Use the generator rule.
- Check that the direction is along the vertical rod.
Starting with upward motion, rightward field and into-page current, state the effects of reversing motion only, field only, and both.
Give me a hint
A single reversal changes the sign; two restore it.
Compare my reasoning
- Motion only gives out-of-page current.
- Field only gives out-of-page current.
- Both give into-page current again.
Motion only: out; field only: out; both: in.
Look for these in your work
- Evaluate all three cases.
- Retain conventional-current and page conventions.
Common mistakes
- Use the right hand for the stated generator convention.
- Dots are out; crosses are in.
- Induced current and electron motion have opposite directions.
What can you explain now?
Upward motion and rightward field produce which induced conventional-current direction in the stated generator arrangement?
Compare with the explanation
Into the page
The motion-cross-field direction is into the page for that perpendicular geometry.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Use stated geometry and the generator right-hand convention, distinguishing imposed motion, reaction force and electron motion.
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.