Magnatism

Question 1

In a compass, what is the pointer magnet called?

Answer 1

Needle

Question 2

What is the type of compass called when used to plot the magnetic field lines?

Answer 2

Plotting compass

Question 3

On a plotting compass, what denotes the north pole?

Answer 3

An arrowhead

Question 4

What are magnetic field lines called?

Answer 4

Lines of magnetic flux

Question 5

What are the properties of magnetic flux lines?

Answer 5

They repel each other sideways
They try to shorten themselves
They always take the path of least reluctance
They appear to originate at the North Pole and terminate at the South Pole
They never cross each other
They always form closed loops
There is no known insulator to them

Question 6

What are Weiss domains?

Answer 6

Iron consists of many very small magnets – known as Weiss domains – within which all the magnetic fields of the individual atoms are aligned in the same direction (Domain Theory).

Question 7

Explain how a permanent is created?

Answer 7

An iron bar that is not magnetised is made up of small magnets that are not aligned and cancel each other out. However if it is exposed to a strong magnetic field the small magnets align and no longer cancel each other out and a permanent magnet is created.

Question 8

What is the curie temperature of iron?

Answer 8

769 degrees c

Question 9

What is the curie temperature of Nickle?

Answer 9

356 degrees c

Question 10

What is the curie temperature of Cobalt?

Answer 10

1075 degrees c

Question 11

What is the curie temperature of some ferrites?

Answer 11

50-600 degrees c

Question 12

What are the three types of magnets?

Answer 12

Ferromagnets
Paramagnets
Diamagnets

Question 13

What is a ferromagnet?

Answer 13

Ferromagnetic Materials: are natural magnetic properties of iron. The term ‘Ferro’ comes from the Latin for iron, ‘ferrum’.

Question 14

What is a ferromagnetic material?

Answer 14

A ferromagnetic material is one that readily magnetises (its constituent atoms easily orient their electron spins to conform to an external magnetic field force – hence Easily magnetised).

Question 15

What is a soft ferromagnetic material?

Answer 15

Soft ferromagnetic materials become demagnetised spontaneously when removed from a magnetic field.

Question 16

What is a hard ferromagnetic material?

Answer 16

Hard ferromagnetic materials can retain their magnetism, making them useful in the production of permanent magnets.

Question 17

Among the natural magnetic minerals, which has the strongest magnetism?

Answer 17

Magnetite

Question 18

What is the tendency of a material to remember their magnetic history called?

Answer 18

Histerysis

Question 19

What is the reminiscence of a material?

Answer 19

The fraction of the saturation magnetisation which is retained when the driving field is removed is called the remanence of the material and is an important factor in permanent magnets. The terms Hysteresis and Remanence is covered in a later submodule

Question 20

What is magnetostriction?

Answer 20

Ferromagnetic materials respond mechanically to an impressed magnetic field, changing the length slightly in the direction of the applied field. This property, called magnetostriction, leads to the familiar hum of transformers as they respond mechanically to AC voltages, and various frequencies.

Question 21

What materials are common ferromagnets?

Answer 21

Most of the ferromagnetic materials are metals. Common examples of ferromagnetic substances are iron, cobalt, and nickel. Metallic alloys and rare earth magnets are also classified as ferromagnetic materials.

Question 22

What are Paramagnets?

Answer 22

Paramagnetic Materials have a small and positive susceptibility to magnetic fields. These are metals that are weakly attracted to magnets.

Question 23

What are common Paramagnets?

Answer 23

They include aluminium, titanium, oxygen and iron oxide.

Question 24

Explain the magnetism of Paramagnets?

Answer 24

The atoms of these substances contain electrons most, but not all, that spin in the same direction. This gives the atoms some polarity. They are only weakly influenced by a magnetic field, for example you couldn’t pick up a tiny piece of aluminium with a magnet. Since some of the atoms can be turned to point their poles in the same direction, these metals are very weak magnets. Their attractive force is only measured with sensitive instruments.

Question 25

What is a Diamagnet?

Answer 25

Diamagnets are repelled by a magnetic field. If diamagnetic materials are placed in a magnetic field, an induced magnetic field occurs in the opposite direction, causing a weak repulsing force.

Question 26

What materials are typically Diamagnets?

Answer 26

These are materials that would normally be considered non-magnetic, such as water, plastics and many metals such as gold, copper and mercury.W

Question 27

What is the unit of flux?

Answer 27

The webber

Question 28

What are magnetically hard materials?

Answer 28

Materials that are difficult to magnetise and demagnetise are described as “magnetically hard”

Question 30

What are magnetically soft materials?

Answer 30

Materials that are easy to magnetise and demagnetise are known as “magnetically soft”.

Question 31

What is coercive force?

Answer 31

Coercive force is the amount of reverse magnetic field needed to return a material’s magnetic flux to zero.

Question 32

What is the formula for coercive force?

Answer 32

Coercive force = retentive x remenence