Force on a current-carrying wire
A current-carrying wire gets pushed in a magnetic field.
When a current-carrying wire is perpendicular to a magnetic field, the Ampère force on it is F = BIL. Its direction is given by the left-hand rule and is perpendicular to both the current and the field. The suspended rod is in equilibrium under the Ampère force, gravity and the tension in the suspension wires, and the deflection angle satisfies tanθ = BIL/(mg). Reversing the current or the field reverses the force.
This is a static model: forces and the graph update as soon as you change a parameter.
Ampère force vs. current
F is proportional to the current with slope BL; negative values mean the force points the opposite way.
Think about it
If the current is reversed, which way will the rod swing?
To the opposite side. The direction of the Ampère force depends on both the current direction and the field direction; changing just one of them reverses the force. Try setting the current to a negative value.
Model assumptionsUniform magnetic field · Wire perpendicular to field · Rod mass 50 g · Static equilibrium
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.