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Magnetism. Physics La Ca ñ ada High School Dr.E. Magnetism 1. 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

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La Cañada High School


magnetism 1
  • 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
properties of magnetism
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
magnetism is safe

Some companies sell magnetic materials that attach to your body to help relieve chronic pain.

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
magnets attract iron
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
magnet has two poles
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
magnet electrical difference
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
magnetic field nature
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
magnetic domains
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
  • 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
measuring magnetic strength
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
detecting magnetic field
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
detecting magnetic field15
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
electric currents and magnetic field
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.
electric currents and magnetic field 3
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
magnetic levitation
Magnetic Levitation
  • Trains float above guide way due to magnetic field
  • Travel at speeds of up to 300 mph (500 kph)
magnetic forces on moving charged particles
Magnetic Forces on Moving Charged Particles

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

magnetic forces on current carrying wires
Magnetic Forces on Current Carrying Wires
  • Moving electrons in wire are pushed up, or down, depending on their direction
measuring currents
Measuring Currents
  • Coils of current-carrying wires set up magnetic field perpendicular to plane of coil
  • Compass needle aligns itself with the field lines
current measuring apparatus
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
earth as a giant magnet
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."
earth s magnetosphere layer 4
Earth’s 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

earth s magnetic field 5
Earth’s 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
  • 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
magnetic pole location
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
earth s magnet flips
Earth’s 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
sun s magnet field
Sun’s 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
  • 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

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

cell phones and pagers
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.
  • Magnetism information fromSchool for Champions Website by Ron Kurtus (revised 29 January 2002)@, 4/15/04
  • Magnetism: Chapter 9by Joseph F. Alward, PhD, Department of Physics, University of the Pacific @, 4/15/04
  • HyperPhysicsby Carl R. (Rod) Nave Department of Physics and Astronomy Georgia State University @, 4/15/04
  • Creation of the UniverseThe Qur’an and Lifeby Harun Yahya @ , 4/15/04
  • Earth’s Magnetic Field by Windows to the Universe, Last modified June 3, 2003@ , 4/16/04
  • Windows to Universe by Windows to the Universe, Last modified June 3, 2003@, 4/16/04
  • New clues to Earth's magnetic flip-flopsby CNN News, April 7, 2004@, 4/16/04