`BL=mu_(0)I_(e)` is intresting by which consequences ?

Explanation

(1) If we consider infinite wire as an axis it implies that the field at every point on a circle of radius r is same in magnitude. In other words, the magnetic field possesses what is called a cylindrical symmetry. The field that normally can depend on three coordinates depends only on one which is on r coordinate.
(2) The field direction at any point on this circle is tangential to it. Thus, the lines of constant magnitude of magnetic field form concentric circles which directly provides a theoretical justification to Oersted.s experiments.
(3) Even though the wire is infinite, the field due to it at a non-zero distance is not infinite. It tends to blow up only when we come very close to the wire. The field is directly proportional to the current and inversely proportional to the distance from the infinitely long current source.
(4) There exists a simple rule to determine the direction of the magnetic field due to a long wire. This rule called the right hand rule is state below.
"Grasp the wire in your right hand with your extended thumb pointing in the direction on the current. Your fingers will curl around the direction of the magnetic field".