Nexus Research Group

Magnets

A magnet sticks to the fridge holding up this weeks shopping list. What are the "strings" pulling them together?

"Black Magic"

The black iron sand from Taranaki beaches contains, funnily enough, lots of iron! Get a plastic petri dish (or a sheet of plastic wrap, sheet of OHT, or a small plate!) and sprinkle on a little sand. Move side-to-side over two magnets and see the iron sand reveal the magnetic of lines of force!


If you have ever played with two magnets, you will have noticed that turned one way the two magnets pull themselves together by some invisible force. They are attracted together if a North pole faces a South.	Flip one of them around and they are pushed away from each other. They are repelled. 8 year old Kimberley describes this as "bumpy air". Two South poles facing each other also repel.

Our lines of magnetic force (in blue) are drawn with arrows to indicate the direction a North Pole would move if free to do so. Therefore, in the photo on the left, a North pole moves toward a South. The photo on the right shows two North poles move away from each other.

HINT: To prevent iron sand sticking to magnets, wrap them first in a few layers of plastic wrap.

The "Magnetic Bottle"

Here is a neat trick that can show up the invisible lines of force that occur around magnets in 3 dimensions.

Boil a 1.5% agar solution in a clear glass jam jar or bottle and allow to cool to about 48oC (just before it is setting).
Add fine iron fillings and mix well.
Put a magnet up against the outside and pour in the agar to set.

The iron fillings will line up eventually becoming trapped in the setting agar, making the magnetic force field plainly visible! You could try using gelatine instead of agar.

Another idea is to cut up iron wool into tiny fibres and put them into a bottle of Baby Oil. If the fibres are too big they will sink, so try different sizes. Once you have shaken the bottle to suspend the fibres in the oil, place a magnet nearby.

PREDICT: Ask your students "What will the lines of force look like when a north and a south pole are close to each other?"
OBSERVE: Let them carry out the demonstration once they have drawn what they think will appear.
EXPLAIN: What does this show us? (seniors might like to consider the physics behind the concept of lines of force)

PREDICT: Ask your students "What will the lines of force look like when a north and a north pole are close to each other?"
OBSERVE: Let them carry out the demonstration once they have drawn what they think will appear.
EXPLAIN: What does this show us?

Magnets

"Black Magic"

The "Magnetic Bottle"

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