What do magnetic field lines “look” like (simple case)?

Suppose you have 1A DC current flowing through 1 inch of straight wire. Physics textbooks always show circular, concentric magnetic lines around the wire at a cross-section “slice” of the wire where the direction of the lines is determined by the right-hand rule.

In reality, the lines extend across the entire length of the wire. So are the “lines” really discrete or are they continuous like a cylinder (length-wise) ? If not, then what’s the distance between the lines along the length of the wire? Also, what’s the distance between the concentric lines for a given cross-area?

I’m not even sure if these are meaningful questions but it’d help me to visualize what inductance really is (# of magnetic lines divided by current).

Thanks.

The magnetic field “lines” aren’t really lines at all. The lines as drawn are just indicative of the direction in which the magnetic field acts at that location. In the radial direction, they can be drawn arbitrarily close together. The magnetic field exists at any given distance, so a magnetic field line could be drawn anywhere. If you looked between two magnetic field lines, there is no reason you couldn’t draw another line there.

If the magnetic field around the entire wire were drawn, it would normally be drawn with discrete lines because that is the convention. However, the magnetic field itself is actually continuous, with strength that varies with distance from the wire. The lines do not indicate that the magnetic field is not present in the spaces between the lines; they are just a visualization aid.

Creating UML Use Case Diagrams