SIR I WANT TO ASK A QUESTION THAT WHY MAGNETIC FIELD LINES CHANGES IN  CIRCULAR LOOP OR STRAIGHT CURRENT CARRYING WIRE AND WHAT ARE THEIR POLES WHEN ELECTRIC CURRENT IS PASSED THROUGH IT.

We know that a current carrying wire is able to deflect a magnetic compass needle. So we can conclude that a current flowing in a wire always gives rise to a magnetic field around it. The magnetic field lines around a straight conductor carrying a current are concentric circles. The direction of the magnetic field produced in the wire depends on the direction of the current flowing in the wire. 

Similarly, when a current is passed through the circular loop of wire, a magnetic field is produced around it. The magnetic field lines form concentric circles. The circles become larger and larger as one moves away from the loop. If the direction of current around the face of circular wire flows in clockwise direction, then that face of the wire will be South pole. If the direction of current around the face of circular wire flows in anti-clockwise direction, then that face of the wire will be North pole.