A bar magnet consists of two poles. Outside the magnet, the lines of force originate from the north and terminate at the sourth pole. Inside it, the lines of force travel from south to north pole forming a closed continous loop. A solenoid consists of a number of insulated circular loops joined together forming a helical structure. Each current carrying loop acts like a magnetic dipole.All the north poles of coils face in one direction and south poles in the opposite direction. the effect is added and one end of the solenoid behaves like a north pole and the other behaves like a south pole. each loop of the solenoid can be considered as a tiny bar magnet and the complete solenoid acts as a larger bar magnet. the line of inside the solenoid the lines of force are directed from the south to north pole. hence, the pattern of lines of force of a solenoid is similar to that of bar magnet.
