Read Current in a Field: Add Segment Forces as Vectors
For a wire made from straight segments in a uniform magnetic field, compute each force I L cross B and add the vectors—not their magnitudes.
Electricity questions depend on identifying charge, a conducting path and the condition that controls current or magnetic effect.
Magnetic effects have two poles and a direction
Like poles repel · unlike poles attract
Like poles repel and unlike poles attract. Keep the field direction and the material’s magnetic property separate.
Start with the condition
Choose each segment's directed length vector from the current direction. For a uniform field, the net force also equals I times the end-to-end displacement cross B.
Build the governing relation
Resolve the given field into components before crossing it with the wire displacement.
Finish with a physical check
Check the limiting case before selecting an option: remove the special feature in the diagram or make the relevant parameter very large or very small. The result should reduce to a familiar relation.
OlympIQ exam lens
- ✓State the physical condition before choosing a formula.
- ✓Keep direction, sign and constraint information explicit.
- ✓Test one limiting case before committing to an option.
Using the total bent length as one scalar length loses the direction information that the cross product needs.
Ready to try the pattern?
100% coverage across the linked question.
Practise the linked question