PRS20 Dipole in Field The current carrying coil above will move 1. upwards 2. downwards 3. stay where it is because the total force is zeroPRS20 Dipole in Field µ N S N S (2) Coil will move down EITHER: The I ds x B forces shown produce a net downward force OR: Think about magnets…PRS20 Loop in Changing Field The magnetic field through a wire loop is pointed upwards and increasing with time. The induced current in the coil is 1. Clockwise as seen from the top 2. CounterclockwisePRS20 Loop in Changing Field (1) Current is clockwise. This produces an “induced” B field pointing down over the area of the loop. The “induced” B field opposes the increasing flux through the loop – Lenz’s LawPRS20 Loop in Changing Field The magnetic field through a circular wire loop is pointed upwards and decreasing with time. The induced current in the coil is 1. Clockwise as seen from the top 2. CounterclockwisePRS20 Loop in Changing Field (2) Current is counter-clockwise. This produces an “induced” B field pointing up over the area of the loop. The “induced” B field opposes the decreasing flux through the loop – Lenz’s LawPRS20 When the coil is below the magnet and moving downwards. This induces a current as pictured. The I ds x B force on the coil is 1. Upwards 2. Downwards 3. ZeroPRS20 (1) Upwards Lenz’ Law: Must oppose motion – force is up More detail: Induced current is counter-clockwise to oppose drop in upward flux. This looks like a dipole facing upward, so it is attracted to the other
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