Magnetic Fields in Wires

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Magnetic Fields in Wires
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Strength of Magnetic Field

• Strength of the magnetic field produced by a
  current carrying wire is directly proportional to
  the amount of current
• Inversely proportional to distance from the wire
  (r)
• Varies by a constant ?o/2?
• ?o permeability of free space
• 4? x 10-7

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Equation

• B (?o/2?) (I / r)

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Example

• A vertical wire carries a current of 25 A up.
  What is the magnitude and direction of the field
  at a point 10cm to the right of the wire?

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Forces Between 2 Wires

• Since wires produce magnetic fields when a
  current is applied, two current carrying wires
  will either attract or repel

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Current In Same Direction

• Wires attract

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Currents in Opposite Directions

• Wires repel

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Forces Between Wires

• F/ l (?o/2?) ( I1I2/ L)
• l length of wires
• L distance between wires

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Example

• Two wires of a 2.0 m long appliance cord are
  3.0mm apart and carry a current of 8.0A. What is
  the force between the wires?

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Example

• A horizontal wire carries a current of 80A. A
  second wire 20cm below it must carry a current I2
  so that it doesnt fall due to gravity, what is
  this current? The lower wire has a mass of .12g
  per meter.