Magnetism

The Nature of Magnets

Magnetic Poles -- two ends where the magnetic effects are the strongest
                           -- one pole is labeled North the other is South

--- magnetic forces are similar to electric forces and fields in that like forces will repel and unlike will attract

Magnetic Fields -- the lines of magnetic force extend from the north pole and encircle the magnet and enter the south pole
                            -- iron filings around a bar magnet are often used to display these lines of magnetic force

Magnetic Materials

     - iron, steel, cobalt and nickel are all material that are attracted readily to magnets and make good magnets
       themselves

ferromagnetic- the most highly magnetic materials are called

     - temporary magnets are made from soft iron, they magnetize easily but lose their magnetism quickly
     - other materials that are harder to magnetize stay magnetized for much longer and therefore are called permanent
       magnets
 
  - many permanent magnets are made of a mixture of cobalt, copper, and iron called alnico

domains - groups of atoms within a magnet, with magnetic fields arranged in the same direction

--- each domain is like a miniature magnet with its own north and south poles

--- in unmagnetized materials, the domains are aligned in many different directions, canceling each out
 
--- in magnetic materials the domains all flow in one direction so the magnetic field is multiplied creating a larger
     magnetic field around the whole piece

--- if a nonmagnetic piece of ferromagnetic material is placed inside a magnetic field, its own domains will begin to
     align with the field surrounding it, making it magnetic
 
--- permanent magnets can lose their magnetism by actions which cause their domains to become unaligned, such as
      heating, banging, improper storage (mixed up magnetic fields)

The Earth as a Magnet

     - over time people have tried to explain why magnetic material when left free to move always pointed in the same
     direction
     - in 1600 a physician named Gilbert proposed that the Earth was itself a magnet and therefore had magnetic fields
     that would influence other magnetic material
     - today we know this to be true, the Earth is like a magnet with lines of magnetic force and a magnetic field that is
     strongest near the north and south magnetic poles
     - remember that the magnetic poles are not at the same location as the geographic poles
     - scientists have been able to study Earth's magnetic fields over time by studying magnetic rocks that have
     solidified leaving a permanent record of any changes
     - Earth's magnetic field has reversed itself many time in its history, every half million years or so
 
 

Compasses      - compasses are magnetic and will therefore be attracted to the opposite pole      - for this reason, the Earth's North Pole is actually the magnetic south pole and this explains why the north      compass needle will always be attracted to the North Pole      - as mentioned, the geographic pole is different from the magnetic pole      - this difference is called magnetic declination and must be taken into account when using a compass over large distances

The following chart provides approximate magnetic declination values for Northern North America.

Other Sources of Magnetism in the Solar System

     - magnetic fields have been found throughout the galaxy and in our own solar system
     - both Saturn and Jupiter have magnetic fields that are greater than Earth's
     - the sun also shows a magnetic field that extends far above its surface
     - where the magnetic field is strong and breaks through the surface, the spots cool and appear darker
     - these sunspots always occur in pairs ( north and south) and sunspot activity varies in an eleven year cycle which
       coincides with the time period for the sun's magnetic field to switch places

** Intense sunspot activity often adversely influences radio and TV communications on Earth (remember magnetism
and electricity appear to be different forms of the same thing!)

magnetosphere -- region of the Earth's magnetic fields

aurora -- charged particles from the sun penetrate the Earth's magnetic fields

Chapter 21: Electromagnetism

Magnetism From Electricity

- there is a relationship between electricity and magnetism called electromagnetism

Oersted's Discovery

- when a compass is placed near a wire carrying electricity, the compass needle was deflected

Electromagnets

- - if a wire carrying electricity was coiled, then the magnetic field around each individual loop would be added to
the one beside it creating a strong magnetic field, just like a magnet

-- a long coil of loops is called a solenoid and produces a magnetic field just like a bar magnet when electricity 
is passed through the coil

-- the solenoid could be turned off and on with the current

electromagnet - - a solenoid with a magnetic material within it 

How do you increase the strength of an electromagnet?

1. winding more coils
2. increasing the current
3. coiling the loops tighter together
4. changing the material in the center (the core)

** the greatest increase in the field occurred if a piece of iron was placed in the solenoid, creating a magnet out of
the iron

--- the field of the coil of wire, plus the magnetic field of the new magnet together created a field hundreds or
thousands of times stronger than the coil itself

Question ?? 

If magnetism can be produced from electricity, why can't electricity be produced from magnetism?

Electromagnetic Induction

-- electricity can be produced in a coil of wire by moving a magnet within the coil
-- electrical generators work on this principle