Earth's Magnetic Poles

Ferrite Bar Magnets
Science Experiments

Reports that other planets may support life always refer to the presence of liquid water.  What is almost never mentioned is whether these planets have a strong magnetic field protecting them. This is one of the key reasons why Earth has an atmosphere and Mars doesn’t. This feature is important and simple bar magnets can demonstrate the nature of the Earth’s magnetic field.

Types of Bar Magnets

Bar magnets, for the purpose of this discussion, are longer than they are wide or thick and have North & South poles on the ends. They are made from a number of materials but cost, strength and durability are all variables to be considered.

Chrome steel bar magnets are ideal for showing magnetic field lines using iron filings. However, they demagnetize easily when dropped or pushed together for repulsion experiments. A remagnetizer can fix this but is an added expense. This problem and the cost of the magnets themselves have made them harder to find.

Alnico (aluminum nickel cobalt) bar magnets are quite a bit stronger & do not demagnetize as easily. They are more expensive than chrome steel though but are still readily available. They are excellent for attraction and repulsion work.

Neodymium bar magnets are the most expensive but even the poorest quality ones are much too strong for working with iron filings when used to represent Earth’s magnetic field. More importantly, when used in attraction experiments, they can come together with enough force to shatter them or any finger caught in the middle.

Chrome Steel Bar Magnets
Typical chrome steel bars. Note the keepers at each end. These were required so magnets would not weaken while kept in storage.

Ferrite Bar Magnets

A popular choice that combines the right strength and price are ceramic ferrite bar magnets. Their main disadvantage is they will break or chip if dropped onto a hard surface.  Another consideration is that not all ferrite bar magnets are created equally. Improper magnetization can leave them so weak as to be next to useless.

Ferrite Bar Magnets
Inexpensive ferrite bar magnets are suitable for attraction-repulsion and paperclip pickup. Be careful not to drop on to a hard surface such as concrete as they are quite brittle and will chip or crack. They do not require special storage or handling otherwise.

We provide three sizes of ferrite bars magnets that are suitable for science experiments. It is for this reason we include paperclip pickup test results to support thim claim.

Paperclip Pickup Test Results

Forty paper clips were placed in a 500ml beaker. A single 75x18x6.5mm ferrite bar magnet was dipped into the beaker to pick up as many paper clips as possible. An average of 22 were pickup up over 5 trials. Plastic coated paperclips do not pick up as well uncoated.

Type Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average
Uncoated Steel 19 18 21 28 22 22
Plastic Coated Steel 13 11 13 9 9 11

Repulsion Test Results

Two 75x18x6.5mm bar magnets were held down with similar poles in contact (e.g. N:N) . They were released & the separation distance caused by the repulsive force was measured. Your results will vary depending on the smoothness of the underlying surface. You can try coating with oil or grease to make friction a factor in your experiment.

Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Average
46mm 44mm 43mm 42mm 44mm 44mm

Video of Test Results

Standard Lego™ parts were used to build a test track to constrain the bar magnets during repulsion. This method is shown in the video as well how we picked up the paperclips.

Another Way to Do Repulsion

Adding 20x10x5 neodymium rare earth block magnets to the ends of the 120mm long bar magnets greatly increased the repulsive force. We were able to achieve 150-200mm (6-8″) of repulsion distance compared to less than 50mm (2″) without the boost.

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Brand Name
Indigo Instruments
Product Name
Ferrite Bar Magnets
Price
USD $2.00
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Available in Stock

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