Action of a magnetic field on a current-carrying conductor
A force acts on a current-carrying conductor placed in a magnetic field; it is called the Ampère force. If the conductor is perpendicular to the field lines, the force is F = B·I·l: B is the magnetic induction, I the current, l the length of the conductor in the field. From this B = F/(I·l), so 1 T = 1 N/(1 A · 1 m): 1 T is the induction of a field that acts with a force of 1 N on a 1 m long conductor carrying 1 A. The direction of the force is found with the left-hand rule: hold the left palm so that the field lines enter the palm and the four fingers point along the current; then the thumb, turned by 90°, shows the force direction. The force direction changes if we reverse the current or the field. These experiments are done only under the teacher’s supervision with a low-voltage source.
Draw 3 diagrams in your notebook for the left-hand rule: field lines entering the page, current to the right; then current to the left; then the field reversed. Find the force direction in each.