Physics Chapter 21 Section 2 Pages 770-772

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PhysicsChapter 21 Section 2Pages 770-772

• Electromagnetism and Magnetic Domains

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I. Electromagnetism and Magnetic Domains

• A. Magnetic Field of a Current Carrying Wire
• 1. When a compass is brought near a wire with no
  current the compass behaves as normal and points
  in the direction of Earths magnetic field.

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• 2. When the same compass is brought near the same
  wire, now with strong steady current flowing
  through it, the compass needle will be deflected
  tangent to the concentric circles of magnetic
  field around the wire.
• 3. If the current is reversed, the compass
  needle will reverse directions

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• 4. This is the Right-hand rule (page 770)
• ? If a wire is grasped in the right hand with
  the thumb in the
• direction of the current, the
• fingers will curl around the
• wire in the direction of the
• magnetic field.
• 5. The magnetic field is in a plane lying
  perpendicular to the wire, and the field is the
  same everywhere on a concentric circle centered
  around the wire.

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• B. Magnetic Field of a Current Loop
• 1. Right hand rule can be applied to a current
  carrying loop.
• 2. Current carrying loop resembles a bar
  magnet

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• 3. Solenoid a long, helically wound coil of
  insulated wire
• ? Produces a strong magnetic field be
• combining several current carrying loops
• ? Acts as a magnet when it carries a current

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• 4. Magnetic field is proportional to
• the number of coils
• 5. The closer the field lines are together the
  stronger the magnetic field

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C. Magnetic Domains 1. Domain a microscopic
magnetic region composed of a group of atoms
whose magnetic fields are aligned in a common
direction.
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• 2. Electrons are constantly spinning and
  therefore create a movement in charge, but in
  most materials they orient themselves so that
  they spin opposite\ directions and their fields
  cancel. ? For this reason, most materials are
  not magnetic

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• 3. In certain metals, the magnetic fields
  produced by the spinning electrons are not
  completely canceled out which leaves a magnetic
  field
• ? Ferromagnetic materials iron, nickel, cobalt
• 4. Usually small areas of neighboring atoms will
  align themselves with similar magnetic fields
• ? Usually small areas
• ? In normal materials, the domains are randomly
  arranged

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Physics Chapter 21 Section 3Pages 773-779
Magnetic Force
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II. Charged Particles in a Magnetic Field

• A. A charge moving through a magnetic field
  experiences a force
• ? Field force (no contact)

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• Equation for finding the magnitude of a magnetic
  field
• B Fmagnetic /qv
• B magnetic field strength
• Fmagnetic magnetic force on a charged
• 
  particle
• q magnitude of charge
• v velocity of charge

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• - SI units for magnetic field strength Tesla
  (T)
• T N/(Cm/s) N/(Am) (Vs)/m2

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B. Applications

• TV picture screens the force on a moving charge
  due to a magnetic field is used to create a
  picture, by use of cathode ray tubes.
• TV video link

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• Loudspeakers magnetic force acting on a current
  carrying wire in a magnetic field produces sound
  waves by continually reversing the direction of
  current and vibrating the speaker cone.

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• Galvanometers device which can be used to
  measure current and/or potential difference by
  using the properties of magnetic forces acting on
  a wire with current moving through it.