Is magnetic field strength directly proportional to the coil or the current?

The strength of a magnetic field won't be directly proportional to the turns in the coil. It is more correct to say that field strength is directly proportional to current through the windings of the coil. There are some "limiting factors" that will not allow this to be a hard and fast rule, but it is essentially correct.


Magnetic field strength (symbol: H) is defined as the magnetomotive force per unit length of a magnetic circuit. As magnetomotive force is the product of the current flowing through a winding and the number of turns, then, yes, magnetic field strength is proportional to both the current and the number of turns -but this is ONLY true over the straight part of the magnetisation curve (i.e. before it goes into saturation).