Magnetism Flashcards
The first magnetic stones were found in ___, near ____
Magnesia, Asia Minor.
This stone is called ____
magnetite.
The earth’s axis poles(Geographic or “True”
poles) and magnetic poles are not aligned.
True or False
True
The _____ is the difference in
alignment between the earth’s magnetic
pole and the axis pole.
angle of declination
Natural magnets became
known as ____ or ____
“leading stones“
or lodestones.
Energy is required to create a magnetic field, but no energy is required
to maintain a magnetic field.
True or False
True
There are only three substances that form natural
magnets: ___, ___, and ____
iron, nickel, and cobalt.
One theory of magnetism states that electrons spin on their own axis
while orbiting the nucleus
True or False
True
This spinning action causes each electron to become a tiny permanent
magnet.
True or False
True
The electrons tend to form pairs spinning in opposite directions. These
pairs negate each other’s magnetism.
True or False
True
Magnetic materials have some electrons that do not have their
magnetism cancelled in a pair.
True or False
True
These magnetic materials (____, ___, and ____) have regions of magnetic
polarity called magnetic ______
iron, nickel, and cobalt, domains
When the magnetic domains are in disarray, the material is not magnetic
True or False
True
The atoms are disarrayed in a
piece of ____ metal.
nonmagnetized
There are 3 classes of magnetic materials:
–
–
–
–Ferromagnetic
– Paramagnetic
– Diamagnetic
Ferromagnetic materials are easily magnetized.
True or False
Examples of these materials are ___, ___ , ___ & ___
True, iron, nickel, cobalt &
manganese.
Paramagnetic materials are not as easily magnetized.
True or False
Examples are ___, ___, and ____
platinum, titanium, and chromium.
Diamagnetic materials cannot be magnetized
True or False
True
Diamagnetic materials can be metal or nonmetal.
True or False
- Magnetic lines of force tend to go around
diamagnetic materials. - Examples of diamagnetic materials are ___, ___, ___, and ____
True, copper, brass,
wood, and antimony
All magnets have two points opposite each other where the field force is strongest: two points where the magnetic flux is
more dense.
These points are referred to as the magnetic ___.
They are the points at which the magnetic lines of force enter and leave the magnet.
It is not possible to have one ___ without having the other
poles, pole
The property that opposes the setting up of flux lines is known as ____
reluctance.
Using this principle, you can construct a path that causes flux to divert around something that you are trying to shield from
magnetic lines of force.
This type of device is called a ____
magnetic screen.
The magnetic lines of force tend to align and concentrate within the ferromagnetic material.
True or False
This causes poles to be established at the points where the lines of force enter and leave the ferromagnetic material.
This process is referred to as magnetism by ____
True, induction.
If the ferromagnetic material is
* soft iron (iron with a low carbon content), the iron is easily magnetized. But it loses its magnetism as the
magnetic field is removed.
True or False
True
- hard iron or steel (with a high carbon content), it requires a much stronger magnetic field to be magnetized.
However, when the magnetic field is removed, the iron material retains most of its magnetism.
True or False
True
Ferromagnetic material can be magnetized in several ways.
*
*
*
- Using electric current
- Stroking with a magnet
- Align and tap
If a piece of ferromagnetic material is placed in the coil and a current is passed through the coil in one direction, the
magnetic field of the coil causes the domains to align in the ferromagnetic material.
True or False
True
Another method of producing a magnet is by stroking a piece of ferromagnetic material with a magnet.
True or False
True
The field of the stroking magnet aligns the domains in the ferromagnetic material, causing it to become magnetized.
True or False
True
A third, and not very effective way to produce a magnet is to align a piece of ferromagnetic material with any magnetic field, even that of the earth, and tap it lightly.
True or False
True
The tapping produces enough energy to align some of the domains with the magnetic field, causing the ferromagnetic
material to become magnetized.
True or False
True
There are also several methods for removing magnetism from ferromagnetic materials.
*
*
*
- Using electric current
- Using heat
- Using vibration
When demagnetizing a piece of ferromagnetic material, you use a source of current that changes direction constantly and
rapidly.
This type of current is called an alternating current(AC)
True or False
True
If you either slowly remove the material from the coil or slowly reduce the current in the coil, then the field becomes
weaker and the domains will be left in a random orientation within the material.
True or False
True
A very effective method of demagnetization is to apply heat to the magnet.
At a certain temperature, called the _____, the molecular structure of the ferromagnetic material rearranges
itself and the alignment of the domains is lost even after the material is cooled.
True or False
Curie temperature, True
Each substance has a different Curie temperature, but for iron it is about ___
770°C.
A third way of removing magnetism is by tapping or vibrating the magnet.
As the material is magnetized, the domains are moved and the bonds are stressed.
When the magnet is vibrated, energy is supplied and the stress tends to restore the domains to their original orientation.
The magnetism is lost.
True or False
Avoid subjecting magnets to conditions that demagnetize them.
This means:
* do not expose magnets to ___.
* do not place magnets near fields created by ___ currents
* do not drop magnets or subject them to excessive ____
* do not store magnets near other ____
heat, alternating, vibration, magnets
Many types of magnets are stored
with a device called a ____
- This is usually a piece of soft iron
placed across the poles of the
magnet to provide an easy path for
the magnetic ___. - If it is not used, the magnetic field
will _____ over time.
keeper, flux, weaken
