When working with inductors in problems, it becomes necessary to determine the direction of the induced emf in a coil (solenoid). Here are some examples of the type of situations with which you should become comfortable.

 

The inductor in all of the examples, is wrapped so that the wires come "down the front" and "up the back" like the coil shown on the left. If the current generated by the circuit changes, then the magnetic field in the solenoid changes and the flux through the coil will change. Remember that the coil ALWAYS reacts to oppose ALL changes in flux lines by inducing an emf that will counter the increase or decrease - thus creating a latency, or inertia.

 

By Zureks (Own work) [Public domain], via Wikimedia Commons

 

As seen in the previous problems, the solenoid (or inductor) acts to resist any changes occuring in the magnetic field flux produced by the current that is passing through its loops. Remember that an emf is ONLY induced when there is a change in the flux; moreover, it is as if the inductor acts as a "temporary variable battery" whose orientation opposes the flux change.

 

The degree to which it provides resistance is called its inductance, L. The emf produced by the inductor is calculated with the formula .

 

 

NOTE: if you did not view the solutions to the previous problems, do so now so you can visualize how the conditions pair together.