I had a doubt about how inductance of a wire is calculated if it is wound around a iron rod, and when its wound around a transformer core.
Case 1 : Considering an iron rod at first , or in other words an electromagnet.
NOTE: Please Ignore the voltage supplied in the images below. For our case I am just asking about a simple coil wrapped around an iron rod without any voltage applied.
Now here flux lines will flow from bottom to top(in the iron rod), and will turn around and flow from Top to bottom(outside the iron rod) to complete the closed loop.
In this case Inductance can just be calculated by using the standard equation
Now My question is in the second case:
Case 2: When the coil is wrapped around the Transformer core.
Now how is the inductance of the coil calculated ? Do we still use the general equation of the inductance or do we use the entire length of the transformer core for our calculation ? NOTE: Ignore coil 2 in the image above.