Magnetism

1
Magnetism

• .

2
Magnetic Fields

• Magnetic fields are historically described in
  terms of their effect on electric charges. A
  moving electric charge, such as an electron, will
  accelerate in the presence of a magnetic field,
  causing it to change velocity and its direction
  of travel. This is, for example, the principle
  used in televisions, computer monitors, and other
  devices with CRTs (cathode-ray tubes). In a CRT,
  electrons are emitted from a hot filament. A
  voltage difference pulls these electrons from the
  filament to the picture screen. Electromagnets
  surrounding the tube cause these electrons to
  change direction, so they hit different locations
  on the screen.

3
Magnetic Dipoles
The north pole of a magnet is the pole that
aligns itself with geographic north. As a result,
the geographic north pole of the earth is
actually very near the earth's magnetic south
pole
4
Lorentz force

• An electrically charged particle moving in a
  magnetic field will experience a force pushing it
  in a direction perpendicular to the magnetic
  field and the direction of motion.

5
Types of Magnets

• Pulsed Magnets
• Pulsed magnets are among the strongest magnets in
  the world, and come in two forms destructive and
  non-destructive. Of these two, non-destructive
  magnets are more suited towards scientific
  research, as they can reach some of the highest
  magnetic fields experimentally possible.
• The energy used by the short pulse magnet is
  stored in the capacitor bank. This bank is
  capable of storing extremely large amounts of
  energy, and is used to discharge (pulse) that
  energy through the magnetic coil. This in turn
  makes the pulse magnet's temperature rise
  greatly, so it is necessary to pulse the
  capacitor bank for a few milliseconds at a time
  in order to keep the magnet's temperature under
  control. However, if too much energy is sent
  through a capacitor bank with a very high
  capacitance, there is a possibility that the
  stress of the magnetic field on the magnet will
  cause it to explode. Also take note that the
  crowbar diode is used to change the flow of
  current from the capacitor to the magnet, from AC
  to DC.

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Types

• Permanent Magnets
• Iron- composed of many microscopic regions
  consisting of numerous atomic dipoles (domains),
  all pointing in the same direction. A strong
  magnetic field will align the domains of an iron
  magnet, or in other words, magnetize it. Once the
  magnetic field is removed, the domains will
  remain aligned, resulting in a permanent magnet.
  This effect is known as hysteresis.

7
Electromagnetic Induction

• The generation of an electromotive force and
  current by a changing magnetic field is called
  electromagnetic induction.
• Faraday confirmed that a moving magnetic field is
  necessary in order for electromagnetic induction
  to occur.

8
Speakers

• Alternating current, generated by a microphone, a
  pickup head, amplifier, radio, or another source,
  flows through the coil of the speaker.
• The current, alternating at the same frequency as
  the sound waves that generated it, induces an
  alternating magnetic field in the coil. As the
  polarity of the magnetic field of the coil
  alternates, it is alternatively attracted to and
  repelled by the permanent magnet. This causes the
  coil to vibrate. The vibrating coil causes the
  attached cone shaped diaphragm to vibrate and
  reproduce the sounds generated by the original
  source.

9
Metal Detectors

• The operation of metal detectors is based upon
  the principles of electromagnetic induction.
  Metal detectors contain one or more inductor
  coils that are used to interact with metallic
  elements on the ground.
• When the magnetic field of the coil moves across
  metal, the field induces electric currents
  (called eddy currents) in the coin. The eddy
  currents induce their own magnetic field which
  generates an opposite current in the coil, which
  induces a signal indicating the presence of
  metal.

10
Strength of Magnets

• The strength of a magnetic field is measured in
  units of Gauss (G), or alternatively, in Tesla
  (T). In the MKS (metric) system of units, 1 T 1
  kilogramampere/second2 104 G
• Strength Distance affected by inverse cube
  of distance from magnet.
• Earth 1 Gauss, Neodymium magnet 104 Gauss
• Technically, Gauss and Tesla are units of
  magnetic induction, also known as magnetic flux
  density. Quantitatively, the force on a charged
  particle q moving with velocity v is given by the
  vector equation F qv x B, where B is the
  magnetic induction.

11
Electricity and Magnetism

• Electric and Magnetic phenomena are intricately
  described by a collection of physical laws, known
  as Maxwell's equations.
• Electromagnetic waves-Light waves are oscillating
  patterns of electric and magnetic fields,
  propagating through space at the speed of light
  (3x108 meters/second).