The rule that determines the direction of a magnetic field produced around a straight conductor carrying current is :

The Right-hand thumb rule (also called Maxwell's corkscrew rule) is used to determine the direction of the magnetic field around a straight current-carrying conductor. If the thumb of the right hand points in the direction of current flow, the curled fingers indicate the direction of the magnetic field lines around the conductor. Fleming's left-hand rule gives the direction of force on a current-carrying conductor in a magnetic field, while Fleming's right-hand rule determines the direction of induced current in a generator. Hund's rule pertains to electron filling in atomic orbitals.