Use the sandpaper to remove the plastic coating from about 1cm of each end of the wire (do this ahead of time for younger students). You will see the silvery-copper wire colour underneath.
Starting at the head of the nail, leave about 7cm wire sticking out, then wind the wire around it in tight turns. Move slowly down the nail, until all but the last 7cm is coiled - it will make about 80 turns. It does not matter if the coils lie on top of each other, though the tighter they are packed together the better.
Keep the coils pushed towards the head of the nail so that when winding is done, the pointed end of the nail is still exposed.
Secure the coil onto the nail with pieces of masking tape. (Skip the tape if galvanized nails are used, as the coils stay tight on the rough nail surface). Make sure that there is about 7cm straight wire sticking out at each end of the coil.
Fold over each end of the sandpapered wire ends so that the pointy end is tucked away. Fold a small piece of aluminum foil around the ends of the wire to cover the ends. The foil will help to make the connection between the copper wire and the battery.
Hold the foil-coated wire ends over the ends of the battery to make electricity flow through the coil, then touch the pointed tip of the electromagnet against smaller nails and paper clips.
Note that the battery becomes hot if it remains connected for a while so make sure it is disconnected frequently.
This activity drains batteries very fast (there is not much resistance in the wire).
Optional: set up stations that the students spend a few minutes each at:
nails large and small - the electromagnet will be able to pick up fewer larger nails than smaller ones
pennies - a mixture of years will mean that some will be picked up by the electromagnet and some not
paperclips - plastic coated and not
items with different kinds of metal (steel, aluminum foil) so that only some will be picked up e.g. fish from magnetic fishing game
How it works:
When there is electricity from the battery flowing through the copper wire, the coils make a magnetic field, which is significant with the many turns. This magnetic field turns the large nail into a magnet, strong enough to pick up small nails, paperclips etc.
Break the circuit by removing one wire from the battery. The nail is no longer magnetic and it drops the objects. (Sometimes a weak residual magetic field remains in the nail, so a few objects remain attached.)
For more detailed explanation see www.wonderhowto.com/how-to/make-simple-electromagnet-326803/
Uses of electromagnets: buzzers/door bells, speakers, cranes in metal recycling yards, maglev train. http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/keeping_th…