Hi this is Ben Finio with Science Buddies
and if you want to know what an electromagnet
is and how they work, then this video is for
you.
You might already know about regular magnets.
They have opposite poles that attract, similar
poles that repel, and they can even attract
other metal objects that don’t attract each
other, like these paper clips.
You can also take a compass, which is itself
a small magnet, and move it around near another
magnet, and the needle will point in the direction
of the magnetic field.
So how does a coil of wire manage to behave
the same way?
It turns out that moving electrical charge,
or current, creates a magnetic field.
Watch what happens when I connect this piece
of wire to a battery.
It makes the compass needle move just like
a magnet did, so we know the wire must be
creating a magnetic field.
This magnetic field takes a circular shape
around the wire like this.
However, the magnetic field around a single
straight wire is very weak, not enough to
pick up even one of these paper clips.
You can make the magnetic field much stronger
by wrapping the wire into a coil called a
solenoid.
This causes the fields around each individual
turn of wire to make a much stronger, more
uniform magnetic field similar to that of
a bar magnet like this.
However, you’ll see that this coil of wire
is still too weak to pick up an individual
paper clip.
To make an electromagnet really strong, you
need to add a ferromagnetic core like this
iron bolt.
Ferromagnetic materials have many smaller,
individual magnetic domains.
Normally these domains are aligned randomly
and cancel each other out.
However, in the presence of an external magnetic
field, these domains align with each other
and the external field, making the overall
field much stronger.
Watch what happens when I insert this iron
bolt into the core of my electromagnet.
Now it’s finally strong enough to pick up
a paper clip.
Unlike a regular magnet, an electromagnet
can be turned on and off by removing the flow
of electrical current.
If you reverse the direction of the electric
current, you reverse the direction of the
magnetic field.
To change the strength of an electromagnet,
you can change the number of turns in the
coil, the length of the coil, the amount of
current flowing through the coil, or the core
material, all of which would make a great
science project.
Because they have very low resistance, the
wires in electromagnets can get very hot,
so you should always disconnect them when
not in use.
The paper electromagnet in this video was
just for a demonstration, but you should not
try this at home because the paper could actually
catch on fire.
To see a variety of science projects that
use electromagnets, as well as instructions
for thousands of other science and engineering
projects, visit us online at www.sciencebuddies.org.
