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Principles of Electromechanics Electricity Motion Electricity Motion: Motor Motion Electricity: Generator Magnetic Field & Faraday’s Law
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Magnetic Field 1.Generation of magnetic field Permanent Magnet: Electric Current: using right hand rule to determine the field direction Straight current Current coil N S
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Current Motion: Current in magnetic field Magnetic field will exert a force on a current Magnetic field will exert a force on a moving charge × × × I F -q V F r
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Circular Motion: Plane B × × × -q V F r Circular path: V || =0 Helical path: V || 0
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Charges in B field: Applications Mass Spectrometer: Cyclotron (accelerator)
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Example: Rail Gun Acceleration: 5 10 6 g Final speed: 1 km/s Duration: 1 ms
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Motion Current: Generating Electricity (Faraday’s law) 1. A current appears only if there is relative motion. 2.Fast motion produces a greater current. 3. Clockwise/counter clockwise current with north pole move in/out. Opposite with south pole. Induced current in secondary coil, if there is change of current in the primary coil: switch or ac current Transformer
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Faraday’s Law of Induction Magnetic flux through area A Amount of magnetic field passes through an area A Faraday’s Law of Induction: An emf is induced in a loop when the magnetic flux that pass through the loop is changing. The the loop is conducting, then a current will flow. For uniform B:(Weber, or Wb, or T m 2 For a loop with N turns: Change B (change current)Change AChange angle between them
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Current loop in magnetic field: Motors BB F F L w
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Torque on a Current Loop: Motors B F F B F F B F F n n n
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Torque on a Current Loop: Continuous B F F n B F F n B F F B FF B F F n
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