CURRENT · MAGNETIC FIELD · FORCE
Current-carrying conductor.
A wire in a magnetic field. Follow the current, watch the electrons, and find the force.
The conductor in the field
Conductor
Fleming’s left-hand guide Linked rotation
Index · fieldMiddle · currentThumb · force
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→ Conventional current I→ Magnetic field B→ Magnetic force F⊖ Electron drift · opposite to I
Drag to rotate · scroll or pinch to zoom · arrow keys rotate the focused diagram. A dot (⊙) points towards you; a cross (⊗) points away.
Arrow lengths and electron motion are illustrative. Turning the camera changes only your viewpoint. When arrows line up in the view, rotate to separate them.
What determines the force?
B is the magnetic field strength, I is the conventional current, and L is the length of straight conductor within the uniform field. The angle θ is measured between the current and the field.
Change the angle
At 90°, the force is greatest for the chosen B, I and L. Parallel or opposite directions give zero force. Increasing B, I or L increases the force in direct proportion.
Reverse the direction
Reverse either the current or the magnetic field and the force reverses. Reverse both and the force returns to its original direction. Electrons in the metal drift opposite to conventional current.
About this model
This is a straight section of conductor in a uniform external magnetic field. A source maintains the chosen current; its return circuit is outside the view. The conductor is held in place to make the force direction clear. Electron dots illustrate net drift, not their full microscopic motion or a measured drift speed. The wire is drawn at a fixed visual length for clarity; L sets the actual length used in the force calculation.
Hand model: “Left Hand Rule” by mHafiz0809, CC BY 4.0. Adapted for orientation and display.
Explore magnetic force on a wire
Adjust current, magnetic field strength, conductor length and their relative directions. Compare conventional current with electron drift and rotate a textured left-hand guide alongside the conductor. Explore the motor effect in IB Physics, A Level Physics and AP Physics 2 or AP Physics C: Electricity and Magnetism.