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I have the following example from a textbook:

1. The path of magnetic field strength developed in a conductor loop is given by the formula H = (I*N*R^2) / (2*sqrt(R^2+x^2)^3)

I = current

N=number of turns

R=radius of loop

x=distance from the center.

Now, my textbook says "If a soft iron core is inserted into a coil-all other things remaining equal-then the force acting on a magnetic needle will increase. I*N remains constant and therefore so does the field strength. However, the flux density "B" -the total number of flux lines-which is decisive for the force generated has increased."

So if the magnetic force acting on a magnetic needle increases, why does not the field strength increase. And what exactly is the difference between H and B. Does anyone know any good web sites, tutorials etc on electromagnetism, inductive coupling.

t.