Using Ferrofluid to Demonstrate Magnetic Fields

Curious about dancing ferrofluid as dark as a black hole? Of course you are! Keep reading! Unfortunately, the phenomenon of magnetism is hardly perceptible in daily life. Although magnetic field lines offer a conceptual aid for understanding, it still remains unclear how magnetic fields manifest in space. In our set-up we tried to show visually the effects of magnetism in a way you could only dream of (until today) and in this instructable we will learn you how to make it yourself! The basic principle is making 2 highly densed coils, connected to a DC Power Supply and adjustable resistors. By adjusting the resistance, the current through the coils will alter, which in turn alters the magnetic field strength. Be aware: soldering is required! Also a slightly important side note: ferrofluid is a very sticky substance which cannot be removed easily (read: almost impossible).

Good luck, be careful, but more importantly: enjoy!

First, gather all the things needed for the set-up. Essential building parts are:

1. 2 steel bolts (diameter 1.2 cm, length 15 cm)
2. 0.5 mm diameter conducting copper wire
3. 2 adjustable resistances (between 50Ω and 100Ω)
4. A wooden plate (around 25 x 25 cm)
5. 2 wooden blocks (height: around 20 cm)
6. 2 screws (minimum)
7. 2 stand clamp holder

And the following tools:

1. 2 DC Power Supplies (maximum of 30 V & 1A)
2. A soldering iron
3. A glue gun

The most essential part of this project is winding the coils, so let's do that first. You will be needing the wire and the bolts. To achieve at least a magnetic field strength of 0.5 T - bearing in mind that the power supply can generate a maximum current of 1A - 4000 windings per meter is chosen.

In order for the coil to work, the wrapping does not have to be done very precisely, but try to count while doing it! Overlapping wires while wrapping should not be a problem. Make sure that the steel is not showing at any place and that the 'thickness' of the wiring covering the steel is the same at every point.

The thing is: the coil works even though the thickness of the wiring is not uniform over the whole length of the bolt. However, if you wind the coil very carefully and make sure that the thickness is uniform, the magnetic field will be more uniform.

Almost done? Check if the thickness of the coil is uniform!

Finally: make sure you leave a piece of wire (about 20 cm) at each end to attach to the power supply and the resistor.

Now that we have the finished coils with a steel core, we can start putting everything together by mounting the coils to the wooden blocks.
Drill a hole in the wooden blocks and secure the adjustable stand clamp holders in place with their accompanying bolts. The hole should be approximately at half the height of the wooden blocks; the exact height does not matter since the final height of the coils can be adjusted easily with the stand clamp holders.

Glue the wooden blocks to the wooden plate at the 'halfway line' of the plate like pillars. Place the blocks with the clamps facing each other at an equal distance from the center of the plate on the 'halfway line'.

Note! The copper wire of the coil has a thin enamel layer (insulating layer) around it, so scour this layer off the copper wire for good connection.

Connect the adjustable resistors to the coils by soldering one piece of wire each to the right tab of the variable resistors. To be able to connect the coils to the power supply, another piece of wire must be soldered to the middle tab of the resistor.

For extra aesthetics it is possible to make a nice dial out of cardboard or paper to read the ohmage of the variable resistor.

Glue the variable resistors face-up on the wooden plate. Make sure there is enough space under and around the resistors as these can get hot.

For the finishing touches a perplex plate needs to be attached to the top of the wooden blocks for putting the ferrofluid on top, while the coils remain visible.

The ferrofluid needs to be put in a plastic container. This fluid is very nasty and is very hard to remove from your hands and clothes.

Dont forget to turn off your glue gun and soldering iron.

For using the set-up the wires from a, the coil, and b, the variable resistor, need to be connected to a DC power supply. By turning these on and cranking the voltage way up, spikes in the ferrofluid should appear. If not, check if your variable resistor is turned down. By regulating the resistance, the height of the spikes is directly affected by the change of current through the coil.