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MAGNETISM

MAGNETISM. What is the cause of magnetism?. The motion of charges cause magnetism. Example: Currents, spinning electrons. An electromagnetic phenomenon where moving charges produce a magnetic field. Magnetic Field: A region where a moving charge can experience a magnetic force.

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MAGNETISM

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  1. MAGNETISM

  2. What is the cause of magnetism? • The motion of charges cause magnetism. Example: Currents, spinning electrons. An electromagnetic phenomenon where moving charges produce a magnetic field. Magnetic Field: A region where a moving charge can experience a magnetic force. The terms magnetism and magnetic field are synonymous with each other.

  3. Types of Magnetism • The magnetism exhibited by materials can be classified as diamagnetic, paramagnetic, or ferromagnetic.

  4. Diamagnetic Materials • All electrons are paired so there is no net magnetic field. • In the presence of an extremely strong external magnetic field, the electron paths are slightly altered, causing a small repulsion of the material. • Magnetic properties are lost after an external magnetic field is removed.

  5. Paramagnetic Materials • A few electrons are unpaired so there is a very weak magnetic field. • In the presence of an extremely strong external magnetic field, the electron paths are slightly altered, causing a small attraction of the material. • Magnetic properties are lost after an external magnetic field is removed.

  6. Ferromagnetic Materials • Many electrons are unpaired so there is a moderate magnetic field in various regions of the material called domains. • A domain is a region with approximately 1020 electrons, the size of approximately 1 mm2. • In the presence of an strong external magnetic field, the electron domains align resulting in a strong magnetic field within the material. • Magnetic properties are retained long after the external magnetic field is removed. • Iron, cobalt, and nickel are ferromagnetic.

  7. Why aren’t all materials ferromagnetic? An electron pair. In most elements the electron pairs spin in opposite directions, cancelling the magnetic field produced by the other electron. Electron Spin In ferromagnetic materials: There are many more unpaired electrons thus resulting, in a strengthened magnetic field. Ex Iron Which elements are ferromagnetic? Iron, Cobalt, and Nickel

  8. Domain: A region with approximately 1020 electrons (approximately 1 mm2). In magnetic materials, the magnetic fields in the domains are arbitrarily orientated causing the element to have a weak magnetic field. An external magnetic field. A magnet is created by subjecting a magnetic material to a strong external magnetic field causing the domains to become aligned. S N

  9. Heat and/or sharp blows can cause the domains to become unaligned. An alloy ALNICO (Aluminum, Nickel, and Cobalt) will make a magnet permanent once the domains are aligned. S N

  10. Magnetic field lines are imaginary lines to show the magnitude and direction of magnetic force. N The direction of a magnetic field is the direction that a compass will point if placed in the magnetic field. S Magnetic field lines are always directed away from the north towards the south. The magnetic field lines always form closed loops (continuous). The magnetic field is said to be north-seeking. S N North-seeking refers to the geographic north of the Earth. N S There are always two poles to magnetic fields, north and south.

  11. Earth’s Magnetic Field S N Earth’s geographic north is near the magnetic south. Earth’s geographic south is near the magnetic north.

  12. Various Magnetic Field Line Orientations S N S N N S The magnetic field between equal strength unlike magnetic poles is uniform. Magnetic Field Lines between two North Poles. N S S N

  13. Magnetic Pole Force Law • Like poles repel. • Unlike poles attract

  14. The Magnetic Field • The magnetic field is denoted by the letter B. • The SI unit for the magnetic field is measured in the unit called a Tesla (T). • The Tesla is part of the MKS system of units • The older unit used for the magnetic field was a Weber/m2 (Wb/m2). 1 T = 1 Wb/m2 • A Tesla made up of the fundamental units of kg/As2 which come from a (kg m/s2)/[(As)m/s] • The magnetic field is a vector quantity. • 1 T=104 Gauss • A Gauss is the cgs measurement of a magnetic field.

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