RADI 121 Test 3 (In Progress)

What is this?

• Magnetite

• Fe3O4

• Natural magnet

• Lodestone or “leading stone”

The earth creates a magnetic field due to naturally occurring ____ mainly iron, at its core

Ores

Any charged particle in motion creates a ________ field

Magnetic

The magnetic field lines of a charged particle is _____________ to the motion of that object

Perpendicular

The lines of a magnetic field are always…..

Such a field is called a bipolar or _______; it always has a north and south pole

Closed loops and never intersect

Dipolar

If the particle's motion is a closed loop, as with an electron circling a nucleus, the magnetic field lines will be perpendicular to the plane of the _____ __ _____

Plane of motion

Electrons rotate on an axis

• Properly called ____

• Creates a ________ moment

• This spinning electric charge is the basis for ___

Spin

Creates a magnetic moment

Basis for MRI

'“Spin” creates a magnetic field which is neutralized (cancelled out) if an ________ pair exists in any shell

Electron

Atoms having an odd number of electrons in any shell exhibit a small ________ field/________ moment

Magnetic field/magnetic moment

A small magnet created by the electron spin is called a magnetic moment or magnetic ______

Dipole

Approximately ___ atoms make up a single dipole (1 million billion)

10^15

Magnetic dipoles are ________ aligned or distributed

Randomly

When acted upon by an external magnetic field, the magnetic dipoles in an object will _____

Align

With ferromagnetic materials, you not only have magnetic dipoles aligned, but also have magnetic _______ that align

Domains

Ferrous materials have ____ domains, but in different directions

Many

What happens if you bring a non-ferromagnetic material in close proximity of a bar magnetic?

No disturbances occur as no domains align

What happens if you bring a ferromagnetic material in close proximity of a bar magnet?

The magnetic field lines that are normally deviated will align along with their domains

What is this?

No-magnetic material

(No domains to align)

What is this?

Magnetic material

(Has domains; but not lined up)

What is this?

Magnet

(Domains are aligned)

The magnetic dipoles in a bar magnet generate imaginary (invisible) lines of ________ field

Magnetic

These magnetic fields, lines of force, or lines of flux always flow from _____ to _____ outside a magnet and _____ to _____ within the magnet

North to South outside the magnet

South to North within the magnet

The stronger the magnetic field, the _______ number of flux lines and the closer together these lines of flux

These lines of force never intersect

Greater

Flux lines _____ each other when they are going in the same direction and _______ each other when going in opposite direction

Repel each other when going same direction

Attract each other when going opposite direction

Magnets are classified according to the origin of the magnetic ________

Property

What are the 3 principal types of magnets

1. Naturally occuring magnets

2. Artificially induced “permanent” magnets

3. Electromagnets

Examples of naturally occuring magnets

Magnetite - exhibits strong magnetism

Earth - relatively weak magnetism

Examkles of artificially-induced permanent magnets

Produced by charging them in the field of an electromagnet

Ex: bar and horseshoe magnents made of iron, compass

Are permanent magnets actually permanent?

Not necessarily. Magnetic property can be destroyed by heating it or by shock impacts that jar them from alignment.

Electromagnets

A coil or wire wrapped around an iron core, which intensifies the magnetic field

Temporary magnets are produced by moving _______ ________

Electric current

Only a magnet when the current is flowing

Ex: detent locks with x-ray machines

Nonmagnetic description and examples

Unaffected by a magnetic field

Glass, plastic, rubber, wood

Diamagnetic description and examples

Weakly repelled from both poles of a magnetic field

Water, Beryllium, Bismuth, Lead, Copper

Paramagnetic description and examples

Weakly attracted to both poles of a magnetic field

Gadolinium, Platinum, and Aluminum

Ferromagnetic description and examples

Can be strongly magnetized

Iron, Nickel, Alnico, Cobalt, Ceramics

Permeability

The ability of a material to attract the lines of magnetic field intensity

Susceptibility

The ease in which a substance or material can be magnetized

Retentivity

The ability of a material to stay magnetized

What is the relationship between retentivity and permeability

Inversely proportional

Repulsion-Attraction

Like poles repel, opposites attract

Inverse Square Law (in terms of magnetism)

If distance is doubled, the magnetic force is decreased by a factor of 4, vice versa

Dipoles: Magnetic Poles

Every magnet has 2 poles: North and South and can be divided in half over and over again and still be a magnet; poles still exist

Ferromagnetic objects can be made into magnets through the process of _________

Induction

When ferromagnetic objects are placed into a magnetic field it is ___________ made into a magnet

Temporarily

What type of magnetism does copper have?

Diamagnetic

How do ferromagnetic materials retain their magnetism when removed from the external magnetic field?

Properly tempered by heat and exposed to an external field for a long period of time

The stronger the magnetic fielf the ____ lines of flux

The stronger the magnetic field the ______ the flux density

Greater

Greater

What 2 factors is flux density determined by?

Field strength and by the area in which the flux lines are located

Magnetic Flux Density Equation

Field strength/area

Weber

SI Unit of magnetic flux

1 Wb = 10^8 lines of flux

Tesla

SI Unit of flux density

Gauss

British Unit of magnetic flux density

1 Tesla = ______ Gauss

10,000 Gauss

Ordinary refrigerator magnet strength

0.1 Tesla

Earth's magnetic field strength

0.0001 Tesla

Much weaker than refrigerator magnet

MRI strength

0.3-2.0 Tesla or higher