Magnetism

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Magnetism

• Physics
• La Cañada High School
• Dr.E

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Magnetism1

• Magnetism is a force that attracts certain metals
• Magnets have two poles that act both similarly
  and differently than electrical charges act
• Easy to detect magnetism, although it is not easy
  to measure its strength
• Make a magnet by rubbing steel against another
  magnet

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Properties of Magnetism

• Magnetism is a force that attracts iron, nickel
  and cobalt
• Combinations of these metals as alloys can become
  permanent sources of magnetism
• A lodestone is the naturally occurring magnetite
  that has the chemical formula Fe3O4

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Magnetism is Safe

• Electrical charges can give a person a shock or
  even kill the person
• Magnetism doesn't seem to have any harmful
  effects
• People who claim that magnets are even beneficial
  to your health

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Magnets Attract Iron

• A magnet
• an object made of a material that attracts iron,
  nickel and cobalt, as well as alloys of these
  metals
• both attracts and repels other magnets.
• Magnetic force attracts and repels acts at a
  distance
• A few rare-earth materials such as bismuth are
  actually repelled by a magnet

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Magnet has Two Poles

• Opposite ends of a magnet are called its north
  and south poles
• should be called the "north seeking" and "south
  seeking" poles, because they seek the Earth's
  North Pole and South Pole, respectively
• Like poles repel
• north pole of magnet will push the north pole of
  another magnet

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Magnet Electrical Difference

• Every magnet has a north pole and a south pole
• A magnet always has a N and S pole
• If you cut a magnet in half, each piece will
  still have a N and S pole

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Magnetic Field Nature

• Magnetism originates in the motion of the
  electrons
• Spinning electrons act like tiny magnets
• Cancellation of this effect occurs in most
  materials
• Iron, nickel, cobalt are exceptions

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Magnetic Domains

• The magnetic north-south axes of groups of iron
  atoms line up in the same direction
• Magnetic domains
• Domains are randomly oriented unmagnetized iron

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Magnetization

• An external magnetic field will twist the domains
  into alignment
• Domains are randomly oriented in unmagnetized
  iron
• Incomplete alignment of domains in slightly
  magnetized iron
• Virtually all of the domains are aligned in
  strongly magnetized iron

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Measuring Magnetic Strength

• Not easy to measure the strength of a magnetic
  field
• Gauss meter is used to measure a magnetic field
• meters uncommon due to limited use

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Detecting Magnetic Field

• Iron filings on a piece of paper
• Spread fine iron filings on a piece of paper laid
  on top of a magnet
• Outline of the magnetic lines of force or the
  magnetic field

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Detecting Magnetic Field

• Compass
• Thin magnet or magnetized iron needle balanced on
  a pivot
• needle will rotate to point toward the opposite
  pole of a magnet
• One end marked N and the other S

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A Compass ?Magnetic Field
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Electric Currents and Magnetic Field

• Spinning or rotating electrons are responsible
  for magnetism in iron
• Moving charges set up magnetic fields
• Compasses (bar magnets) line up in circles around
  a wire carrying current.

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Iron Filings form Concentric Circles around Wire
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Electric Currents and Magnetic Field3

• Magnetic field lines around a long wire which
  carries an electric current form concentric
  circles around the wire
• The direction of the magnetic field is in the
  direction the fingers if your right hand curls
  around the wire with your thumb in the direction
  of the current

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Electric Currents and Magnetic Field
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Magnetic Levitation

• Trains float above guide way due to magnetic
  field
• Travel at speeds of up to 300 mph (500 kph)

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Magnetic Levitation
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Magnetic Forces on Moving Charged Particles

• If charge particles move in a magnetic field,
  they experience a sideways force

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Magnetic Forces on Current Carrying Wires

• Moving electrons in wire are pushed up, or down,
  depending on their direction

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Measuring Currents

• Coils of current-carrying wires set up magnetic
  field perpendicular to plane of coil
• Compass needle aligns itself with the field lines

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Current-Measuring Apparatus

• Electromagnet tends to align its north face with
  the iron magnet's south face
• A spring resists this tendency to twist the
  greater the current, the greater the deflection
  of the needle

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Earth as a Giant magnet

• Earth's magnetic field is thought to be generated
  deep inside the planet
• An inner core of solid iron is surrounded by an
  outer core of molten iron
• They rotate at different rates, and the
  interaction between the regions creates what
  scientists call a "hydromagnetic dynamo."

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Earths Magnetosphere Layer4

• Also named Van Allen Belts
• Protects the Earth from celestial bodies, harmful
  cosmic rays and particles
• Belts at thousands of kilometers above the earth
  protect the living things on the Earth
  
• from the fatal energy
• that would otherwise
  
• reach it from space

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Earths Magnetic Field5

• The Earth has a magnetic field with north and
  south poles
• reaches 36,000 miles into space.
• surrounded in a region called the magnetosphere
• prevents most of the particles from the sun,
  carried in solar wind, from hitting the Earth

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Aurora

• High Speed electrons and protons from space
  travel along magnetic field lines
• Field lines are nearly horizontal near the
  equator which protects the atmosphere
• The field lines are nearly vertical at high
  latitude, thus the high speed particles can enter
  the atmosphere

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Magnetic Pole Location

• Location of magnetic pole is not fixed
• Geographic north is called the Earth's North
  Magnetic Pole by convention
• The North Magnetic Pole is actually the south
  pole of the Earth's magnetic field
• the north pole of a compass was defined as the
  pole that points to the geomagnetic north

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Earths Magnet Flips

• Magnetosphere can flip its orientation so that
  the field lines which were pointed toward the
  north pole change and point toward the south pole
• record preserved in magnetic rocks which lie
  along the ocean floor
• Magnetism in these rocks points first in one
  direction, then in another direction, giving the
  ocean floor a stripped appearance (from a
  magnetic point of view
• many times in the past the north pole has become
  the south pole, and vice versa

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The Sun is a Great Big Magnet
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Suns Magnet Field

• The Sun is a big magnet
• During solar minimum the Sun's magnetic field
  resembles that of an iron bar magnet, with great
  closed loops near the equator and open field
  lines near the poles
• The Sun's dipolar field is about as strong as a
  refrigerator magnet, or 50 gauss
• Earth's magnetic field is 100 times weaker

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Sunspots

• Sunspots are places where intense magnetic loops
  -- hundreds of times stronger than the ambient
  dipole field -- poke through the photosphere
• Sunspot magnetic fields overwhelm the underlying
  dipole
• The Sun's magnetic field isn't confined to the
  immediate vicinity of our star
• The solar wind carries it throughout the solar
  system

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Magnetic Fields on the Sun

• Plasma, like iron filings, follows magnetic field
  lines
• Coronal loops created by hot, glowing plasma flow
  along magnetic field lines

The Earth fits inside the loop
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Cell Phones and Pagers

• When there are many sun spots, it is called the
  solar maximum
• lots of solar flares
• strong solar wind
• radiation is also extra strong
• All this solar activity can interfere with radio
  waves
• cell phones and pagers don't work all the time
• can hear solar static on car radio.

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Bibliography

1. Magnetism information from School for Champions
   Website by Ron Kurtus (revised 29 January 2002) _at_
   http//www.school-for-champions.com/science/magnet
   ism.htm, 4/15/04
2. Magnetism Chapter 9 by Joseph F. Alward, PhD,
   Department of Physics, University of the Pacific
   _at_ http//sol.sci.uop.edu/jfalward/physics17/chapt
   er9/chapter9.html, 4/15/04
3. HyperPhysics by Carl R. (Rod) Nave Department of
   Physics and Astronomy Georgia State University _at_
   http//hyperphysics.phy-astr.gsu.edu/hbase/magneti
   c/magcur.html, 4/15/04
4. Creation of the Universe The Quran and Life by
   Harun Yahya _at_ http//www.creationofuniverse.com/
   html/science_06.html , 4/15/04
5. Earths Magnetic Field by Windows to the
   Universe, Last modified June 3, 2003 _at_
   http//www.windows.ucar.edu/tour/link/earth/Magne
   tosphere/overview.html , 4/16/04
6. Windows to Universe by Windows to the Universe,
   Last modified June 3, 2003 _at_ http//www.windows.uc
   ar.edu/spaceweather/location_mag_poles.html,
   4/16/04
7. New clues to Earth's magnetic flip-flops by CNN
   News, April 7, 2004 _at_http//www.cnn.com/2004/TECH/
   space/04/07/poles.reverse/, 4/16/04