To demonstrate the magnetic field of a coil of wire, a lucite board of board is used with no. 10 wire threaded through it to from the coil as shown. the rest of the circuit is the same as for the previous part of the demonstration.  iron filing is sprinkled on the lucite and current is passed through the coil. tapping the lucite will be caused the iron filing lineup parallel to the lines of force. 

Observe that the iron fillings have the same pattern of magnetic fields that existed around a bar magnet. if the iron filling is removed, and the compass needle is placed inside the coil, the needle will along the axis of the coil with the north pole end of the compass pointing to the north pole end of the coil. remember the line of force inside of magnet or coil from the south pole to the north pole.      

The north pole end of the coil can be verified by using the left-hand rules of coils. if the compass is placed outside the coil and moves from the north pole to the south pole, the compass needle will for low the direction of a line of force it moves from the north pole to the south pole. when the current through the coil is reversed, the compass needle will also reserve its direction.  

Review of the electromagnetic field:-

Electromagnetic field:-

current flowing through a wire generates a magnetic field whose direction is determined by current flow. the direction of generating a magnetic field is found by using the left-hand rules current-carrying conductor.

The magnetic field of a loop or coil:-  

A loop generates a magnetic field exactly the same as the bar magnet. if many loops are added in series forming a coil, a stronger magnetic field is generated. the left-hand rules for the coil are used to determine the coil's magnetic polarity.

Field strength:-

Increasing the number of turns of a coil increases the field strength and increases the coil current also increasing the field strength. an iron core may be inserted to greatly concentrate the field (increase the flux density) at the end of the coil. the ampere-turn is the unit used comparing the strength of magnetic fields.

 Permanent magnet and electromagnetic fields:-

Electromagnetic fields are much stronger than the permanent magnet type and are used in most practical electrical machinery. when electromagnets are used, the field strength can be varied by varying the amount of current flow through the field coils.