Magnetism Presentation

This presentation of magnetism has been assembled to help aid in teaching the concepts of magnetism to classes between grades 8 and 12. No equations have been used and the main concepts are described though the demonstrations.

The materials for this presentation can be ordered for usage, by contacting the UBC Physics & Astronomy Outreach Program or the materials can be assembled for less than $200, by using items found at the hardware store, grocery store, and science teacher websites (such as Educational Innovations ).

List of items in the presentation:

8 red/blue ceramic magnets
1 30 x 30 cm magnetic field viewer film
6 15 x 15 cm magnetic field viewer films
1 eddy current tube (1 m x 2.5 cm ID copper pipe with 2.5 cm wide strip of magnetic viewing film)
1 2.5 cm x 2.5 cm cylindrical stainless steel
1 2.5 cm x 2.5 cm cylindrical neodymium magnet
1 odd shaped neodymium magnet
1 2 cm spherical neodymium magnet
1 2.5 cm disk neodymium magnet
100 1 cm disk neodymium magnets
1 8 x 8 cm copper coil (100 turns)
1 9 volt battery
1 floating ring magnet set
1 levitron top (very difficult to master)
1 lodestone
1 500 ml of olive oil
1 9 cm cork disk
2 3 cm compasses
2 2D magnetic field viewers (made of 2 salad container tops with a tea spoon of iron filings inbetween)
1 3D magnetic field viewer (made of 1 clear rectangular container filled with baby oil and 2 tea spoons of iron filings)
1 container of iron filings
1 package of overheads of the pictures used in the presentation

Please Note:

The larger neodymium magnets are extremely strong, caution must be heeded as they are capable of bone crushing forces!



What is a magnet?

Pass out a couple of magnets (blue/red or the 1 cm disk neodymium magnets) for self exploration.

Definition of a Magnet
- OBJECT: Piece of metal that attracts metal. A piece of metal that has the power to draw iron or steel objects toward it and to hold or move them (msn Encarta).

Definition of Magnetism
- ACTION: The force exerted by a magnet. The phenomenon of physical attraction for iron, inherent in magnets or induced by a moving electric charge or current.
- Force of magnetic field: the force exerted by a magnetic field (msn Encarta).

Eddy Tube Demo

This is the coolest demonstration of the presentation's collection.

- Click on the image to play the movie clip.

- Start with the magnetic viewing film not showing.
- Ask the class how fast objects fall due to gravity (9.8 m/s). Objects should fall though the tube (1 m) in less than 1 sec.
- Drop the stainless cylinder through the tube to confrim this fact.
- Before droping the neodymium cylinder: ask the class whether it drops faster, slower or stops through the tube, then drop it. It will take about 9 secs to fall.
- Ask why the magnet might move slower through the tube (remember gravity affects ALL OBJECTS equally) and the copper tube is not paramagnetic (uneven spins, which permanent magnetic material must have) but diamagnetic (paired spins).
- Try different magnets, each one will have a different magnetic shadow and fall at different times.: sphere: 4 sec., disk: 16 sec., odd shape: 3 sec.
- Ask why the different magnets might fall through the tube at different times (It has to do with shape and size). The tighter the fit in the tube the slower it will travel through it.
- Also notice that instead of the magnets falling at a constant acceleration, they are falling with nearly constant velocity, which means a repelling force is involved which is negating the force of gravity.
- More principles of magnetism need to be explored before an answer can be fully formulated.

Pass out magnet and viewing film.

- The magnets handed out can be either the red/blue or the 1 cm disk neodymium magnets.
- The magnetic viewing will not show a shadow for any other material, it only works with magnetic materials.
- It is similar to iron filings in a gel, wrapped in two sheets of plastic.
- Please note: The film is not transparent and will not show up on the overhead.

What materials are magnetic ?

The elements known for being magnetic are of 3d and 4f spin of the periodic table.

Iron (26)

Iron is the most common metal used for making magnets. It is abundant and easy to magnetize.

Cobalt (27)
Nickel (28)
Iron, Cobalt, and Nickel are known as the ferromagnetic metals.
Neodymium (60)
Gadolinium (64)
Neodymium and Gadolinium are known as the Rare Earth magnets.

Are magnets made of individual types of magnetic material?

Most magnets are are made up of several elements.
  - Alnico
- Ceramic
- Neodymium [Nd2Fe14B]
These are just a sample of the the many different permanent magnets.

Can a rock be magnetic?

Yes, its called Lodestone or Magnetite.

Pass out the lodestone. Notice the iron filings that stick to it.

Use the compass to find the rock's North and South pole.

Place the rock on the magnetic viewing film to see its magnetic shadow.

Lodestone is ferrimagnetic.

Are there other kinds of magnets besides permanent magnets?

1. Electromagnetic

- When an electric current is passed through a wire, the current creates a magnetic field.
- The higher the current, the stronger the magnetic field created.
- The loops in the wire help focus and strengthen the field created by the current.
- Demonstate the coil on a piece of magnetic viewing film.

A. B. C.
- If the coil is connected to a multimeter and a magnet is passed through the center of the coil, the multimeter will show a current induced by the magnet. This current is dependent on how quickly the magnet moves and the orientation of the magnet.
- This is a big hint in what is happening in the eddy tube demonstration.

2. Super Conductive

Such magnets are used in MRIs.

What uses do magnets have?

Ask the the class to answer this question. There are magnets in most of the items we use in every day life.

The mouse and the large magnet can be used to show how magnets can be used for special effects, such as in movies, séances etc.
- Click on the image to play the movie clip.
- Demonstrate the mouse moving by placing a magnet under the table. Move the magnet under the mouse (rotate, turn etc) to see which way the mouse will move.

The tower of circular magnets can be used to show how the level of the magnets can be used as a barometer (the distance between the rings is proportional to the force exerted by the atmosphere), or as a spring.

The magnetic top can be used to show how magnets can be used to push/pull (similar to the electromagnets of a Maglev), or how the idea of perpetual motion machines cannot exist (if the top cannot keep spinning indefinitely, which has the minimum of friction associated with it how can any other mechanism possibly be more efficient at using energy).
- Demonstration of this top requires much practise.

Where did the magnet get its name from?

Noted in Greek literature 2300 years ago. Named for the Magnates, inhabitants of Magesia, where lodestone was abundant.
Some other interesting facts:
Lodestone was recorded as being used for water navigation as far back as 1030 AD by the Chinese mathematician Shen-Kua.

The lodestone would be placed on cork in a bowl of oil, where it would rotate until it was lined up with the Earth's magnetic field, showing the sailor's the direction of magnetic North.
- Click on the image to play the movie clip.
- Demonstrate the lodestone compass.

- 1600’s the first published text on magnetism by William Gilbert. It was more on the curiosities of magnetism then on the physics.
- 1800’s Joseph Henry and Michael Farady established the connection between magnetism and electricity.

Their names are used for the measure of coils and capacitors respectively. This is the start of the era of electromagnetism.

- 1873 James Maxwell wrote the text describing Henry’s and Faraday’s discoveries, which in turn led the way to the development of the generator (Edison) and the electric motor.
Even though magnetism has been studied for over 400 years it is still not fully understood.

How do magnets work?

The magnetic properties of elements come from their valance electrons
  - The electrons have a spin either up or down.
- When these spins line up it creates a magnetic moment.
- When enough of the elements in the metal have moments in the same direction, the metal is said to be magnetized.
Aligned moments create a magnetic field.
Parallel non-aligned moments (center) are "anti-ferromagnetic"
Random moments (right) noncollinear magnetism.
  - Magnets are dipole (north – south)
- Monopoles are theoretically possible, and research is trying to create one but so far scientists have not been able to achieve creating one.

What is the magnetic field?

Magnets have attractive/repelling forces associated with them

Demonstrate the magnetic field lines with with the 2D viewer
- Before putting the 2D viewer over the magnet, try to spread the iron filings out by shaking the viewer lightly.
- Pass out the red/blue magnets and the 2D viewer.
- Ask the class if they know what the field lines look like when 2 magnets are placed pole to pole (North - South, North - North, etc).

- The force is strongest at the poles.
- The magnetic forces create magnetic field lines (represent the lines of force).
- This region in space is where the magnetic force can be detected.
- Magnetic field lines are complete curves perpendicular to magnetic force.
- Magnetic field lines never cross.
- Direction is south to north.
- The closer together the lines the stronger the force.
- The strength of a magnet is proportional to 1/R^2.

What is the strength of some magnets?

Strength is measured in 1Ns/Cm (Tesla) or (Gauss) symbol B
  - Fridge magnets (100 - 400 gauss)
- Neodymium magnets (1 - 2 T or 10k – 20k Gauss). They are 15 – 30 times stronger than ceramic magnets (the most common). It is the strongest permanent magnet available.
- Super conducting magnets can reach field strengths as high as 13.5 T. (used in MRI)
- Pulse magnets provides a magnetic field as high as 72 T.

Eddy Tube Demo revisited - So how does it work?

Much of the explanation on how the eddy tube demo works has been covered in the above presentation; see if the class can come up with the solution.

Just like a current in a wire creates a magnetic force, the moving magnet creates a current in the copper pipe, which in turn creates a magnetic force in the opposite direction. Because the forces are in opposite directions, the magnet’s decent is slowed.

Is the Earth a magnet?

The Earth is kind of like a large magnet.
- The field lines are approximated as the same as a bar magnet, however in actuality, this is not the case.
- The magnetic poles are constantly moving
- At some places on the Earth the poles are reversed
- The liquid metal outer core controls the Earth’s magnetic field.
- The outer core is composed mainly of a nickel-iron alloy, while the inner core is almost entirely composed of iron.
- This outer core is not of constant viscosity or static in movement, but moves and swirls, which causes the variations in the magnetic field.
- The field ranges from .3 Gauss (near the equator) to .6 Gauss (at the poles).

Can objects be magnetizes just by sitting in the Earth's magnetic field?

If the object is made up of ferromagnetic metals, then it is possible.
Have the class check out the garbage can, stools, table (must be metallic) with a compass. If these objects have been in the same orientation for a period of time the compass should swing from pointing South at the top and North at the bottom.

Can magnetism be used to create Art?

You be the judge.

Ferro-fluid Photo

MIT: One inch wide drop of ferro-fluid on a glass slide atop a yellow post-it with a green card held up to reflect another colour. Three magnets are arranged beneath slide - Felice Frankel.

- From "Visions of Earth," National Geographic, November 2005


Aurora Borealis (Northern Lights)
- Occur when highly charged electrons from the solar wind interact with elements in the earth's atmosphere.
- They follow the lines of magnetic force generated by the earth and flow through the magnetosphere, a teardrop-shaped area of highly charged electrical and magnetic fields.
- All of the magnetic and electrical forces react with one another in constantly shifting combinations. These shifts and flows can be seen as the aurora’s "dance,"

- Both of these great photos of the Aurora Borealis were taken by Dick Hutchinson, and his website can be accessed by clicking on either picture.

UBC Physics & Astronomy Outreach Program

(This presentation was put together by Dean Moncado. April, 2006)