What factors affect the strength of
an electromagnet?
As we have seen, due to the alignment
of the parallel lines of force, the magnetic field inside the solenoid
is very uniform and very strong, but only in the coil and the poles at
the ends of the solenoid, so how can we increase the magnetic effect
i.e. make a stronger electromagnet?
(a)
Increasing the current flow
through the coil
The strength of the magnetic field
is increased overall by increasing the current.
Any stream of moving electrically
charged particles naturally creates a magnetic field.
The more charged particles moving
through the wire, the greater the magnetic field effect.
(Don't say by 'increasing the
p.d.' without saying to increase the current!)
(b)
Increasing the number of coils of
wire of the solenoid coil
Many solenoids consist of hundreds of
turns of thin insulated copper wire.
The more coils packed tightly
together, the greater the strength of the magnetic field.
You can do this by (i) increase the
number of coils using the same length of wire OR (ii) you can both
increase the number of coils AND the total length of wire.
(c)
Using an soft iron core - this
makes a practical temporary electromagnet
If you place a rod of magnetic
material like iron, inside the solenoid, the iron becomes an induced
magnet and the magnetic lines of force are intensified through it.
As with the 'empty' solenoid its
self, the magnetic flux is greatest at the ends of the solenoid, which
now coincides with the ends of the magnetically 'soft' iron rod (left
diagram).
The solenoid plus the iron rod
are effectively make a strong 'bar magnet' (right diagram).
As long as the current is flowing the
electromagnetic effect will work.
Switch off the current and the
magnetic effect goes.
This means you can use this system as
an on/off temporary electromagnet that has many useful
applications.
(d)
Decreasing the length of the
solenoid (not the total length of the wire!)
If you can compact the solenoid to a
shorter length for the same number of insulated coils of wire you
increase the intensity of the magnetic field - making the lines of force
closer together.
I don't consider this an important
factor since the insulated coils of wire are usually packed as tightly
together as possible and length might be determined by how it fits into
some device.
In most applications it is factors (b)
and (c) that are employed to increase the effectiveness of the solenoid.
Coil 1. Just a plain solenoid coil,
producing a relatively weak magnetic field.
Coil 2. This solenoid with a soft iron
core, produces a much
greater strength of magnetic field due to the addition of the iron rod.
Coil 3. Using two soft iron rods, or one
thicker one, the field strength is increased even more.
Coil 5. Unlike coils 2. and 3., which are
temporary electromagnets (on/off with current), coil 5 would make a steel
rod a permanent magnet.
Coil 5. could not be used as an
on/off electromagnet, but it is a way of making permanent magnets.
Be able to know, describe and explain, how to
increase magnetic field strength of solenoid coil by increasing the current
flowing through it, more turns of wire wound around, using a soft iron core
and making the coil
more compact.
