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Detection of a Magnetic Field

by Ron Kurtus (revised 23 March 2012)

Any source of magnetism, such as a magnet or electromagnet, is surrounded by a magnetic field. That field can be detected by various devices, which can also give information about the direction of the field and even its strength.

A simple compass can detect a magnetic field and demonstrate its direction. Iron filings can be used to show the shape of a magnetic field. At the sophisticated level, a gaussmeter can detect a field and indicate its strength, as measured in gauss units.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Compass

A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. It can be used to detect small magnetic fields. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.

Using a compass to show the magnetic field

When you bring a compass near an item suspected of being magnetized or having a magnetic field, the compass will turn and point toward the appropriate pole of the object.

Compass needle attracted to magnet's N pole

Compass needle attracted to magnet's N pole

A famous experiment showed that a wire with DC electric current running through it created a magnetic field. When the electricity was turned on, a nearby compass moved to indicate a magnetic field was present.

Earth is a huge magnet

The compass was used to discover that the Earth is a huge magnet. The North-seeking pole of the compass needle will always point toward the Earth's North magnetic pole.

Iron filings

By spreading fine iron filings or dust on a piece of paper laid on top of a magnet, you can see the outline of the magnetic lines of force or the magnetic field. The picture below

 

Iron filings and compasses show the shape and direction of the magnetic field

Iron filings and compasses show the shape and direction of the magnetic field

This experiment also shows that magnetism will act through many materials, such as paper. Would the experiment work if a sheet of iron were used to sprinkle the filings? What about aluminum foil?

Gaussmeter

Gaussmeters are used to measure the strength of a magnetic field. They use a electronic chip called a Hall effect device, which gives off a tiny electrical current when exposed to a magnetic field. The current is amplified with electronic circuitry and a meter shows the number of gauss (the units of magnetic field strength).

These devices are used to detect and measure magnetic fields in scientific experiments, in industry and even in people's homes.

Summary

Magnetic objects are surrounded by a magnetic field. Devices can detected the field and also give information about the direction of the field and even its strength. A compass can detect a magnetic field and show its direction. Iron filings can show the shape of a magnetic field. A gaussmeter can detect a field and indicate its strength.


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Resources and references

Ron Kurtus' Credentials

Websites

How Compasses Work

Build your own Gaussmeter - At-home instructions

Low-cost Gaussmeter - Not that cheap, but you can see information about a gaussmeter

Magnetism Resources

Books

Top-rated books on Magnetism


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


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