Q:

https://www.physicsforums.com/threads/comparing-self-inductance-of-three-solenoids.949177/page-2

#27 and Kuruman, seem to take a strange view on self inductance. In one of your posts, you say that the self inductance of L2 will be very small (rather than exactly zero), which is correct IMO.

- Donald Brown (age 68)

Birmingham, UK

#27 and Kuruman, seem to take a strange view on self inductance. In one of your posts, you say that the self inductance of L2 will be very small (rather than exactly zero), which is correct IMO.

- Donald Brown (age 68)

Birmingham, UK

A:

The discussion you point to is mixed up, as you say. Most of the contributors seem confused about the relation between the inductance of the whole coil and the self-inductances of the parts and their mutual inductance. At any rate, the answer "zero" for the total inductance assumes idealized coils with exact spatial overlap, an impossible situation. In any real coil there will be little regions near the wires with non-zero magnetic fields when curent flows. That means that the magnetic field energy is not zero and therefore the inductance is not zero. It can, however, be much smaller than the self-inductances of the counterwound sets of coils. That's the point the writers were trying to make.

Mike W.

*(published on 06/09/2018)*