Whenever the current is flowing in the solenoid, the magnetic lines of force of different turns strengthened and finally forming a magnetic belt constitutes the strong magnetic flux. The direction can be determined by the right hand rule: thus the north and south poles are shown in Fig. 11. 16. The magnitude Of the flux depends upon the quantity of current and the number of turns in the solenoid.
Polarity of a solenoid
The direction of the north pole or south pole or the polarity can be determined by these following methods.
Right hand rule
In this case hold the solenoid in your right hand so as the tips of the fingers indicate the direction of current in the solenoid then the thumb will indicate the direction of the north pole so produced.
Fig. 11.16. Solenoid.
Screw rule
In this method have a right handed screw, rotates it in the direction of current in the coil then the position of point or tip of the screw will indicate the north pole.
End rule
It is most commonly employed rule for finding out the polarity of the electromagnet. In this method the direction of current in the coil is observed from one side. If the direction of current in the solenoid is clockwise than that end will be south pole and if the direction is anticlockwise the end will be north pole.
Magnetic compass
Bring a magnetic compass near the one end of the solenoid, the attraction or repulsion will take place between the formed pole and the compass, so if the south pole is attracted then the north pole is formed, similarly south pole is determined.