Detection of a Magnetic Field

Any source of magnetism such as a magnet or electromagnet is surrounded by a magnetic field. Information about this field can be retrieved from various devices. A compass can detect a magnetic field. The shape of the magnetic field can be demonstrated with iron filings. A gaussmeter will detect a field and indicate its strength, measured in gauss units.

Questions you may have include:

• How does a compass detect a magnetic field?

• How do iron filings demonstrate a magnetic field?

• What is a gaussmeter?

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.



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



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
A gaussmeter is 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).

Summary
You can detect a magnetic field with a compass, iron filings, or a gaussmeter. The strength of a magnetic field is measured in gauss units.

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