Rad 350: Electromagnetism

Magnetism

The ability of a material to attract iron, cobalt, or nickel

exists whenever electric charges move relative to other objects or relative to a frame of reference

When a charged particle is in motion, a magnetic force field perpendicular to the motion will be created

classification of magnets: natural

earth, iodestone

classification of magnets: artificial permanent magnets

horseshoe magnet, bar magnet, magnetic compass

classification of magnets: electromagnets

temporary magnets produced by means of an electric current

Magnetic states of matter: Non-magnetic

unaffected by a magnetic field

Magnetic states of matter: Diamagnetic

weakly repelled from both poles

Magnetic states of matter: Paramagnetic:

weakly attracted to both poles

Magnetic states of matter: Ferromagnetic:

can be strongly magnetized

FERROMAGNETIC MATERIALS

Iron, nickel, or alloys containing either or both of these elements

When a magnet is brought near to ferromagnetic materials the atoms in the material become lined up (temporarily magnetized) and a magnetic force is produced

ELECTRON SPIN

The nature of magnetic materials is such that the orbital electrons of their atoms spin in predominately one direction

rotation creates a magnetic field

SPIN MAGNETIC MOMENT

A magnetic field is established when electrons spin on their axes

MAGNETIC DOMAIN

When these small magnetic dipoles form groups of similarly aligned atoms

Alignment of the dipoles= acts like a magnet

DIPOLES

Groups of atoms with their net magnetic field moving in the same direction

DOMAINS

An accumulation of dipoles where all are aligned in the same direction

How do you create a magnet

When magnetic materials are placed in a strong magnetic field, the domains align with the external field

NON-MAGNETIC:

Atoms are not magnetic, and no domains are formed, cannot be magnetized

NON-MAGNETIZED MATERIAL:

Domains are in a state of random disorder, but can be aligned to become a magnet

MAGNETIZED MATERIAL:

The domains are aligned in orderly fashion, where poles are facing the same direction

MAGNETIC FIELDS (flux lines)

¨Lines of force flowing through the magnet and to the outside of the magnetic material, forming a three dimensional field

The strength of the magnetic field is measured in the SI unit

tesla (T)

LAWS OF MAGNETISM

Every magnet has two poles (North and South)

Like magnetic poles repel, unlike poles attract

Magnetic field lines are closed loops

A changing magnetic field can produce a current

A changing electric field can produce a magnetic field

MAGNETIC INDUCTION

¨The process by which a material becomes magnetized by the temporary orientation of the dipoles

ELECTROMAGNETISM

A form of energy resulting from electric and magnetic disturbances is space

Any charged motion induces a magnetic field

ELECTROMAGNET

A current carrying coil of wire (solenoid) wrapped around an iron core, which intensifies the induced magnetic field

ELECTROMAGNETIC INDUCTION

Moving a conductor (such as a copper wire) through a magnetic field induces an electric current in that conductor

Faraday's Law

Varying magnetic field intensity induces an electric current

INCREASING THE VOLTAGE: HOW?

Fashioning the conductor into a coil and passing it through a magnetic field
¤Increase the number of coils

Increase the strength of the magnetic field

Increase the speed which the conductor is passed through the magnetic field

Factors for faraday's law

The strength of the magnetic field

The speed of the motion between lines of force and the conductor

The angle of the conductor to the magnetic field

The number of turns in the conducting coil

FLEMING HAND RULES: RIGHT HAND THUMB RULE

If the right hand is used to grasp a wire, the thumb is in the direction of current flow, the fingers indicate direction of magnetic field lines

FLEMING HAND RULES: RIGHT-HAND GENERATOR RULE

If the thumb points in the direction the conductor is moving and the index finger points in the direction of magnetic lines of force field, the middle finger will indicate the direction of conventional current

FLEMING HAND RULES: LEFT HAND MOTOR RULE

States that if the index finger points in the direction of the magnetic lines of force field and the middle finger points in the direction of the conventional current, the thumb will indicate the direction the conductor will move

Electric motor:

an electric current produces a mechanical motion

Generator or Dynamo:

converts the mechanical energy of the motion to electrical energy

transformers:

changes the intensity of alternating voltage and current