what is meant by length of air gap between electromagnetic poles
First of all did you know what does electromagnet means? Electromagnet is a soft metal core prepared into a magnet by passing an electric current through a coil that surrounds (wrap) it. On this principle only solenoids are constructed.
A conductive wire is wounded around a metal rod or a bar and the rod on which the wire is wrapped is known as a solenoid and the resulting magnetic field exude away from this point. So, the length of air gap in between poles is the distance in between the poles. For instance, if you take a horse shoe shaped electromagnet, then the length of air gap becomes smaller than a bar electromagnet.
A conductive wire is wounded around a metal rod or a bar and the rod on which the wire is wrapped is known as a solenoid and the resulting magnetic field exude away from this point. So, the length of air gap in between poles is the distance in between the poles. For instance, if you take a horse shoe shaped electromagnet, then the length of air gap becomes smaller than a bar electromagnet.