solenoid A helical coil of wire with diameter small compared with its length. A steady current passing through the coil produces magnetic field. The field lines of the magnetic field are parallel to the axis of the solenoid and go around it as shown in the fig. s4. The value of the magnetic field, B at the center of the solenoid is given by,
B =m 0 n I/ l (s6)
where n is the total number of turns, I the current and l the length of the solenoid.