MOD 4  LECTURE 4                                    MAGNETISM

In this lecture you will learn about:


"Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles.

A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field.

The magnetic field is produced by the motion of electric charges, i.e., electric current. The magnetic field causes the magnetic force associated with magnets."  wikipedia
 
Magnetism is a force over distance, like mass
It alters space
It has "fields or lines that emanate evenly in all directions

Click HERE for a java showing iron filings aligning in an 
 Electrical magnetic filed

When a + charge and a - charge are within range, 
the fields are distorted in the direction of the attracting forces
 

 
 
 
 
 
 

When two like charges, +/+ or -/- are within range, 
the fields are also distorted, but away from each other

Click HERE for a java showing this


 
WHERE DOES MAGNETISM COME FROM?
"Spin is an intrinsic angular momentum of particles such as electrons, and has an  associated  magnetic field, much like that of a bar magnet." 1 

"In most materials, atoms are arranged in such a way that the magnetic orientation of one electron cancels out the orientation of another. The ferromagnetic iron and its binary iron - chromium alloys are different. Their atomic arrangement is such that groups of atoms band together into small areas called Weiss domains, in which the magnetic moments of atoms ("elementary magnets") are uniformly oriented in the same direction, even without an external magnetic field." 2


1. http://www.physics.sfsu.edu/~senglish/research/spinrelaxation.html
2. http://ankaweb.fzk.de/website.php?page=science_condensed&id=7

 
MAGNETS
Natural magnets are oxides of iron (colored black)

Heating destroys the alignment of iron particles

As lava cools any iron particles align with the existing magnetic field of Earth

Electric magnets are strong enough to pick up cars and can be turned off when they want to drop the car into a crusher.  Also good for separating metals from non-metals. 

TIP: When shopping for used car.  Take along a magnet and test the panels of the car for iron because some cars that have been in an accident have fiberglass fill and the magnet wont "stick". 


 

THE EARTH, THE SUN, MOST OF THE PLANETS ARE BIG MAGNETS
What causes earths magnetic fields?

It has been a classic case of scientific method where the hypothesis and theories have come, been challenged and gone down in flames. 
 

1.  The liquid metal part of Earth's core has been suspected as the source of Earth's magnetic fields  PFFFT.  But molten stuff doesnt have a "charge"
2.  The solid iron core is the source of the fields PFFFT.  The sun and Jupiter dont have an iron core, they do have magnetic fields 
3.  Rotation of earth affects liquid outer core and this produces magnetic field  AHA!: slow rotating planets like Venus and Mercury have weaker magnetic fields than Earth and Jupiter and Saturn, which rotate faster and have stronger magnetic fields.

 
EARTH'S MAGNET AND THE VAN ALLEN BELTS
"The Van Allen radiation belt is a torus of energetic charged particles (plasma) around Earth, which is held in place by Earth's magnetic field. This field is not uniformly distributed around the Earth. On the sunward side, it is compressed because of the solar wind, while on the other side it is elongated to around three earth radii. 

It is split into two distinct belts, with energetic electrons forming the outer belt and a combination of protons and electrons creating the inner belt. In addition, the belts contain lesser amounts of other nuclei, such as alpha particles. The Van Allen belts are closely related to the polar aurora where particles strike the upper atmosphere and fluoresce.

Prior to the Space Age, the possibility of trapped charged particles had been investigated by Kristian Birkeland, Carl Størmer, and Nicholas Christofilos.[1] The existence of the belt was confirmed by the Explorer 1 and Explorer 3 missions in early 1958, under Dr James Van Allen at the University of Iowa. The trapped radiation was first mapped out by Sputnik 3, Explorer 4, Pioneer 3 and Luna 1." wiki

FLARES are huge spurts of hot gas that erupt from areas of sunspots. When they hit the Van Allen belts, they cause a distortion of the magnetosphere.

Van Allen belts (the magnetic field) protects us from SOLAR WIND. solar wind is bare nuclei and electrons, ionic particles that are thrown out by solar activity. MOST solar wind particles are deflected around and past earth.

 


 
MAGNETIC FIELDS/VAN ALLEN BELTS + SOLAR FLARES = AURORA BOREALIS AKA NORTHERN LIGHTS
FLARES are huge spurts of particles that erupt from areas of the sun called sunspots.  When they hit the Van Allen belts, the very energetic charged particles are captured in the Van Allen belts/magnetic fields and travel down magnetic lines into the atmosphere where they smash into air molecules.  Radiation in the visible is given off.   What we see is the AURORA BOREALIS or Northern lights. 

"The collisions in the atmosphere electrically excite electrons to take quantum leaps (a mechanism in which the electron's kinetic energy is converted to visible light); and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most auroras are green and red emissions from atomic oxygen. Molecular nitrogen and nitrogen ions produce some low level red (pink) and very high blue/violet auroras. The light blue and green colors are produced by ionic nitrogen and the neutral helium gives off the purple colour whereas neon is responsible for the rare orange flares with the rippled edges.". wiki

For Aurora alerts click here 


 
WHAT DOES MAGNETISM HAVE TO DO WITH ELECTRICITY?
We would still be burning gas for light and riding horses if the generator had not been invented. The electrical generator depends upon another physical property: MAGNETISM, WHICH IS TOTALLY DEPENDENT UPON MOVING ELECTRONS.
 
This is the crux, the nub, the whole enchilada here. Get a cup of coffee, this is IT.

 
The flow of the electrical charge or field through a wire will induce (cause) a magnetic field. Click HERE to see this

A rapidly rotating magnetic field will induce (cause) an electric current in a wire!  Click HERE to see this

SO, if you use a water (hydroelectric) or steam (from burning coal or nuclear) to turn a wheel, it can rotate a magnet inside of a coil of wire and this will induce the free electrons in the metal wire to move  rapidly back and forth. 

THIS IS ALTERNATING CURRENT. 

While the electrons don't go anywhere, the energy wave or field does. If the wire is grounded, the current will flow in that direction.

NO GROUND, NO FLOW

If there is no movement of electrons (current) in the wire, there is no magnetic field. The faster and the greater the number of electrons that move, the stronger the magnetic field.

Conversely, in a generator, the stronger the magnet and faster it rotates, the stronger the electric current.
 

THE RIGHT HAND RULE, the thumb points in the direction of the flow and the curved fingers the direction of the magnetic field

 

when current flows, the magnetic field is perpendicular to the flow of electrons, the magnetic field wraps around the wire and goes counterclockwise.. the right hand rule

A.C. AND THE EMS 

- Electrical energy waves MOVE AT THE SPEED OF LIGHT like all other waves in the electro-magnetic spectrum.
--- As you watch waves come in on Lake Michigan, there is energy and impact hitting the breakers. But the actual water in each wave is not moving. The energy is in the oscillations of the water up and down and that energy moves forward until the water abruptly stops at the breaker and the kinetic energy is transferred to the concrete in the walls or on the beach.

REVIEW:
MAGNETISM
FIELDS
How is a magnetic field produced?
If electrons are not flowing in a wire, is there a magnetic field?
How can A.C. electricity be induced in a wire?
Is there a magnetic field if there is no amperage?
What is hypothesized to be responsible for Earth's magnetic field?
Magnetism (electrical)
Discuss what you know about the Van Allen belts and how they are involved in Aurora Borealis.
How do the Van Allen belts protect the Earth?