Magnetism

Question 1

The first magnetic stones were found in ___, near ____

Answer 1

Magnesia, Asia Minor.

Question 2

This stone is called ____

Answer 2

magnetite.

Question 3

The earth’s axis poles(Geographic or “True”
poles) and magnetic poles are not aligned.

True or False

Answer 3

True

Question 4

The _____ is the difference in
alignment between the earth’s magnetic
pole and the axis pole.

Answer 4

angle of declination

Question 5

Natural magnets became
known as ____ or ____

Answer 5

“leading stones“
or lodestones.

Question 5

Energy is required to create a magnetic field, but no energy is required
to maintain a magnetic field.

True or False

Answer 5

True

Question 6

There are only three substances that form natural
magnets: ___, ___, and ____

Answer 6

iron, nickel, and cobalt.

Question 7

One theory of magnetism states that electrons spin on their own axis
while orbiting the nucleus

True or False

Answer 7

True

Question 8

This spinning action causes each electron to become a tiny permanent
magnet.

True or False

Answer 8

True

Question 9

The electrons tend to form pairs spinning in opposite directions. These
pairs negate each other’s magnetism.

True or False

Answer 9

True

Question 10

Magnetic materials have some electrons that do not have their
magnetism cancelled in a pair.

True or False

Answer 10

True

Question 11

These magnetic materials (____, ___, and ____) have regions of magnetic
polarity called magnetic ______

Answer 11

iron, nickel, and cobalt, domains

Question 12

When the magnetic domains are in disarray, the material is not magnetic

True or False

Answer 12

True

Question 13

The atoms are disarrayed in a
piece of ____ metal.

Answer 13

nonmagnetized

Question 14

There are 3 classes of magnetic materials:
–
–
–

Answer 14

–Ferromagnetic
– Paramagnetic
– Diamagnetic

Question 15

Ferromagnetic materials are easily magnetized.

True or False

Examples of these materials are ___, ___ , ___ & ___

Answer 15

True, iron, nickel, cobalt &
manganese.

Question 16

Paramagnetic materials are not as easily magnetized.

True or False

Examples are ___, ___, and ____

Answer 16

platinum, titanium, and chromium.

Question 17

Diamagnetic materials cannot be magnetized

True or False

Answer 17

True

Question 18

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 ____

Answer 18

True, copper, brass,
wood, and antimony

Question 19

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

Answer 19

poles, pole

Question 20

The property that opposes the setting up of flux lines is known as ____

Answer 20

reluctance.

Question 21

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 ____

Answer 21

magnetic screen.

Question 22

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 ____

Answer 22

True, induction.

Question 23

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

Answer 23

True

Question 24

• 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

Answer 24

True

Question 25

Ferromagnetic material can be magnetized in several ways.
*
*
*

Answer 25

• Using electric current
• Stroking with a magnet
• Align and tap

Question 26

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

Answer 26

True

Question 27

Another method of producing a magnet is by stroking a piece of ferromagnetic material with a magnet.

True or False

Answer 27

True

Question 28

The field of the stroking magnet aligns the domains in the ferromagnetic material, causing it to become magnetized.

True or False

Answer 28

True

Question 29

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

Answer 29

True

Question 30

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

Answer 30

True

Question 31

There are also several methods for removing magnetism from ferromagnetic materials.
*
*
*

Answer 31

• Using electric current
• Using heat
• Using vibration

Question 32

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

Answer 32

True

Question 33

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

Answer 33

True

Question 34

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

Answer 34

Curie temperature, True

Question 35

Each substance has a different Curie temperature, but for iron it is about ___

Answer 35

770°C.

Question 36

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

Question 37

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 ____

Answer 37

heat, alternating, vibration, magnets

Question 38

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.

Answer 38

keeper, flux, weaken