Choose a positive unit normal to the loop and choose positive circulation by the right-hand rule. Write the applied magnetic field as , where . Because the field is uniform, the external magnetic flux is
Faraday's law of induction gives the induced electromotive force, and Ohm's law gives the current through the loop's electrical resistance:
This is the induced current in a tilted resistive loop with the self-generated magnetic-flux contribution neglected as requested. The factor has units . A field parallel to the loop plane has and induces no current in this uniform-field model.
For , the initial normal flux is positive. At , the external magnetic field is instantaneously zero but its normal component is decreasing, so and . The current is counterclockwise when viewed from the positive-normal side. Its own magnetic field points along through the loop, preserving the initial normal flux in accordance with Lenz's law.
Figure 1.
Initial oblique field and the induced current a quarter-cycle later, for a positive initial normal flux
. Details.
For , both circulation and the induced normal-field direction reverse. The current follows the rate of change of magnetic flux; the quarter-cycle current is nonzero even though the external field itself vanishes then.