A long, wound conducting wire that forms a spiral coil is called a solenoid.
When current i travels, a magnetic field appears inside the solenoid whose induction lines are practically parallel. The magnetic field inside the solenoid is practically uniform.
Under these conditions, at each point inside the solenoid, the magnetic induction vector has the following characteristics:
• direction: it is that of the solenoid adze;
• sense: it is given by the right hand rule;
• Intensity: Where N is the number of turns in length l, the intensity of vector B is given by:
μ is the magnetic permeability constant of the medium;
N is the number of turns of the solenoid;
l is the length of the solenoid;
i is the intensity of electric current.
Like the loop, a solenoid has two poles. Therefore, according to the right-hand rule, the lines of magnetic induction are perpendicular to the center plane of the turns.