Magnetism Grobs

Cards (62)

  • Magnetic field lines are unaffected by nonmagnetic materials such as air, vacuum, paper, glass, wood, or plastics
  • magnetic field lines in a magnetic substance

    is concentrated when a magnetic substance such as iron is placed in the field. Inside the iron, the field lines are more dense, compared with the field in air.
  • the end of the bar magnet is called
    north seeking pole
  • opposite end of the bar magnet is called
    south seeking pole
  • the earth's geographic north pole has

    south magnetic polarity
  • the earth's geographic south pole has
    north magnetic polarity
  • magnetic flux
    The entire group of magnetic field lines, which can be considered flowing outward from the north pole of a magnet
  • magnetic flux
    symbol (phi) ϕ\phi
  • stronger the magnetic field has more lines of force and more flux
  • One maxwell (Mx) unit equals one magnetic field line
  • james clerk maxwell
    proved that electromagnetic phenomena travel in waves at the speed of light.
  • the Weber
    the larger unit of magnetic flux
  • one weber
    1×1081\times10^8lines or maxwells
  • one microweber
    100 lines or maxwells
  • flux density
    the number of magnetic fi eld lines per unit area of a section perpendicular to the direction of flux
  • flux density formula

    B=B=ϕA{\frac{\phi}{A}}
  • CGS unit for flux density
    The Gauss
  • The SI unit of flux density
    The Tesla
  • comparison of flux and flux density

    flux is total area, flux density is specified unit area
  • induction
    The electric or magnetic effect of one body on another without any physical contact between them
  • a permanent magnet can induce an unmagnetized iron bar to become a magnet without the two touching. The iron bar then becomes a magnet
  • Note that the north pole of the permanent magnet 7 induces an opposite south pole at this end of the iron bar
  • permeability
    This ability to concentrate magnetic flux
  • air gap
    the air space between the poles of a magnet
  • The shorter the air gap, the stronger the field in the gap for a given pole strength. Since air is not magnetic and cannot concentrate magnetic lines, a larger air gap provides additional space for the magnetic lines to spread out
  • The purpose of a short air gap is to concentrate the magnetic fi eld outside the magnet for maximum induction in a magnetic material placed in the gap
  • The small part of the fi eld in the air is called leakage flux
  • A toroid is made in the form of a doughnut.
  • The principle of the closed magnetic ring is used to protect permanent magnets in storage
  • keeper for a magnet
    The keeper maintains the strength of the permanent magnet as it becomes magnetized by induction to form a closed loop
  • an alternating fi eld can demagnetize the magnet.
  • The two broad classes are permanent magnets and electromagnets
  • electromagnet needs current from an external source to maintain its magnetic field.
  • permanent magnet, not only is its magnetic field present without any external current, but the magnet can also maintain its strength indefinitely
  • Sharp mechanical shock as well as extreme heat, however, can cause demagnetization
  • Current in a wire conductor has an associated magnetic field
  • With the length much greater than its width, the coil is called a solenoid.
  • More current and more turns make a stronger magnetic field
  • Soft iron is generally used for the core because it is easily magnetized and demagnetized.
  • A relay is a switch with contacts that are opened or closed by an electromagnet.