A solenoid is a
current carry conductor coil closely wound in cylindrical shape. Often inside the space of a solenoid a ferro
magnetic material in a cylindrical shape, is kept to increase the magnetism of
When current is
passed through the solenoid , It generates a nearly uniform magnetic field
inside the coil.
Magnetic fields inside a solenoid
Magnetic field lines through a current carrying conductor loop is
along its axis at its center. As the solenoid of big length and
small radius has a number of coils carrying the same current and have no gaps
in between the windings, the magnetic lines add up.
The resulting magnetic field lines in side the solenoid become
more or less uniform and aligned along the axis of the solenoid. At the
edges they tend to diverge towards the opening. Outside the solenoid the
effects of the neighboring windings cancels out the magnetic field to zero.
Use as an electromagnet
Thus the cylindrical area inside a solenoid is an
electromagnet by itself. We can also wrap a solenoid around a
ferromagnetic material like iron, say, over half or full length of the
bar. The bar can be bent in a shape of a "U"or a "horse
shoe" or a "circle". Then the air gap between the
two ends can be used as a magnetic field.
The empty solenoid can be bent in a shape of a horse shoe also.
The strength of the electromagnet above is increased by
adding more number of windings to the solenoid, increasing the number of
windings per unit length, increasing the current, decreasing the diameter of
It can be increased also by introducing a ferro-magnet of
high paramagnetic property inside the solenoid.
It can be increased by adding another solenoid of larger
diameter around the solenoid.
The strength of an electromagnet can be increased by
immersing the solenoid and surroundings in side a paramagnetic fluid of high
B = μ₀ μ n i , n =
windings/unit length, i = current
the magnetic field as per the right hand thumb rule: is downward into the table. we curl the fingers in the direction of the current, and the thumb points to the direction of magnetic field.