Fleming's Left Hand Rule

2 Key excerpts on "Fleming's Left Hand Rule"

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  eBook - ePub

  Fundamental Electrical and Electronic Principles

  • Jo Verhaevert, Christopher R. Robertson(Authors)
  • 2024(Publication Date)
  • Routledge

    (Publisher)

  Heinrich Lenz (1804–1865) was a Baltic-German physicist and studied electromagnetism, by repeating and carefully expanding experiments by Michael Faraday. In addition to the law named after him, Lenz also independently discovered Joule’s law.

  5.2 Fleming’s Right-Hand Rule

  This is a convenient means of determining the polarity of an induced emf in a conductor. Also, provided that the conductor forms part of a complete circuit, it will indicate the direction of the resulting current flow.

  The first finger, the second finger and the thumb of the right hand are held out mutually at right angles to each other (like the three edges of a cube as shown in Figure 5.3 ). The F irst finger indicates the direction of the F lux, the thuM b the direction of M otion of the conductor relative to the flux, and the sEC ond finger indicates the polarity of the induced E mf and the direction of C urrent flow. This process is illustrated in Figure 5.4 , which shows the cross-section of a conductor being moved vertically upwards at a constant velocity through the magnetic field.

  Figure 5.3 Fleming’s right-hand rule: the cube

  Figure 5.4 Fleming’s right-hand rule: the cross-section of a conductor

  Note: The thumb indicates the direction of motion of the conductor relative to the flux. Thus, the same result would be obtained from the arrangement of Figure 5.4 if the conductor was kept stationary and the magnetic field was moved down.

  Worked Example 5.1

  Q The flux linking a 100-turn coil changes from 5 mWb to 15 mWb in a time of 2 ms. Calculate the average emf induced in the coil; see Figure 5.5 .

  Figure 5.5 The flux as function of the time for Worked Example 5.1

  N = 100 ;   d Φ = 15 − 5 × 10 − 3   Wb ;   d t = 2 × 10 − 3   s

  e = − N d Φ d t = − 100 × 15 − 5 × 10 − 3 2 × 10 − 3   = − 100 × 10 × 10 − 3 2 × 10 − 3   = − 500   V

  Note that if the flux was reduced

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  eBook - PDF

  Guide to Electric Power Generation, Third Edition

  • K.D. Smalling, Anthony J. Pansini(Authors)
  • 2020(Publication Date)
  • River Publishers

    (Publisher)

  Relative Motion of Conductor and fi eld An electrical pressure—or voltage—can be induced in a conductor by moving it through a magnetic fi eld as described above. A voltage can also be induced electromagnetically by moving a magnetic fi eld across the conductor. It makes no difference whether the conductor is moved across the magnetic fi eld or the magnetic fi eld is moved across the conductor. A stationary conductor which has a magnetic fi eld sweep-ing across it is cutting the magnetic fi eld just the same as though the conductor were moving across the magnetic fi eld. Referring to fi gure 6-6(b), it is observed that the conductor mov-ing downward through the magnetic lines of force whose direction is assumed to be from the North pole to the South pole of the magnet has a voltage induced in it such that the circulation of electrons—or electric current—is in the direction indicated. If the conductor is moved upward through the same magnetic lines of force, the voltage induced in it will be in the opposite direction to that indicated above. Thus, it is seen that Generators 201 Figure 6-6b. Right hand rule for generation action. the direction of the induced voltage depends upon the direction of the magnetic fi eld and the direction of motion of the conductor. Right Hand Rule It is convenient to have a rule for remembering the relations in direction between the magnetic fi eld, the motion of the conductor and the voltage induced in it. This rule is usually called the Right Hand Rule. If the right hand is held with the thumb, fore fi nger and middle fi nger all at right angles to each other as shown in fi gure 6-6, the thumb indicates the direction of motion of the conductor through the magnetic fi eld, the fore fi nger indicates the direction of the magnetic lines of force (issuing from the North pole) and the middle fi nger indicates the direc-tion in which a voltage is being generated in the conductor.

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