Magnetic Field due to Current-Carrying Conductor
A current-carrying conductor produces a magnetic field with circular field lines around it; the direction is given by the right-hand thumb rule.
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Circular field around a straight conductor
When an electric current passes through a straight conductor, it produces a magnetic field in the surrounding space. The field lines form concentric circles around the wire, with direction given by the right-hand thumb rule: if you hold the conductor with your right hand and thumb pointing in the direction of current, your fingers curl in the direction of field lines.
Dependence on current and distance
The magnitude of the magnetic field near a long straight conductor is directly proportional to the current (I) and inversely proportional to the distance (r) from the wire: B ∝ I / r for points close to the wire in air or vacuum.
How would the field pattern change if you reverse the direction of current in the conductor?