When the electric current
passes through the wire round around the
nail, it creates a magnetic field that reaches
out in expanding circles. When a wire carrying
electricity is twisted into a coil, it is
called a solenoid. The magnetic field twists
with the coiled wire, causing the magnetic
field lines to concentrate inside the coil.
This creates a powerful magnetic effect
inside the coil called an electromagnet.
The magnetic field inside the coil causes
the tiny magnetic fields in the metal of
the nail to be aligned in one direction
(all the north poles point the same way).
These little fields all pointing in the
same direction add to the coil and make
the magnet strong enough to pick up some
How many paper clips can you pick up by
the electromagnet? What would happen if
you used two batteries and connected them
together (make sure you connect the positive
to the negative poles if you're using the two batteries)?
Try to see how many paper clips you can
pick up. Now, try using the nine-volt battery. (Connect
the positive and negative terminals like on the
How many paper clips can you pick up? Is
there any relationship between the voltage
of the batteries and the number of clips
you can pick up?
* WHAT DOES "PENNY" NAIL MEAN? The term penny (like 10p) originated in England many years ago. Ten penny, four penny, etc., nails got their names from the fact that one hundred nails of that size cost ten pence, four pence, etc. Today penny represents the definite length of a nail measured from the head to the tip of the point. The term penny is still shown by using the English Pence sign p.
** An inexpensive ($2.99) knife switch can be found at Radio Shack (Catalog #: 275-1537) with screw terminals and for low-power use.