Forces on Current Carrying Wires

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Forces on Current Carrying Wires
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• If a current carrying wire produces a magnetic
  field, we should expect that magnets exert a
  force on the wire
• Direction of the force is perpendicular to the
  direction of the current flow and perpendicular
  to the magnetic field

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Right Hand Rule

• Fingers point in the direction of the magnetic
  field, thumb in the direction of the current,
  palm points in direction of the force on the wire

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Magnitude of Force

• Right hand rule tells direction but not amount of
  force
• Force is directly proportional to the current
  (I), length of wire (l), strength of magnetic
  field (B) and also depends on angle between I and
  B

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Equation

• F I l B sin ?
• When I and B are parallel, the sin of the angle
  is 0 so no force is acting
• Force is at its max when I and B are at 90
• Unit of B is the tesla (T)
• 1 T 1 N/ A m

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Example

• A wire carrying a 30 A current has a length of 12
  cm and is placed between the pole faces of a
  magnet at an angle of 60. The magnetic field is
  .90 T. What force acts on the wire?

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Example

• A rectangular loop hangs in a magnetic field
  pointing up. If a current of .245A flows
  counterclockwise through the loop, and a force
  of .0348N acts, what is the magnitude of the
  magnetic field? What direction does the force act?