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Electromagnetic Induction

Electromagnetic Induction. The Discoveries of Michael Faraday and Joseph Henry Showed That a Current Can Be Induced by a Changing Magnetic Field. Faraday’s Law.

nicole-david
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Electromagnetic Induction

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  1. Electromagnetic Induction The Discoveries of Michael Faraday and Joseph Henry Showed That a Current Can Be Induced by a Changing Magnetic Field.

  2. Faraday’s Law • An emf is set up in a closed electric circuit located in a magnetic field whenever the total magnetic flux linking the circuit is changing. • This is called electromagnetic induction. • Induced emf • Induced current

  3. A Galvanometer and a B-Field • Induced current is related to the motion of the conductor in the magnetic field • The direction of the induced current is directly related to the direction of motion of the conductor in the magnetic field • Direction is dependent on the motion of the B-field or the conductor • The motion of the conductor is perpendicular to the B-field

  4. More Thoughts… • If the conductor is moved parallel to B-field, the galvanometer will show no deflection, thus no induced emf or current. • If the conductor is looped several times, the deflection on the galvanometer will increase. • Thus, the rate of motion, the number of loops and the magnitude of the B-field vary directly with the magnitude of the induced current and emf.

  5. Factors Affecting Emf • Emf induced in each coil of the conductor is proportional to rate of change of magnetic flux • Emf = - DF/Dt • Emf = -N(DF/Dt) • Note that negative sign indicates that induced emf is of such polarity as to oppose the change that induced it

  6. Induced EMF • Induced current exists only if wire in a field is part of a circuit. • Thus, if F = BA then F = Bxl • So therefore, Emf = - DBxl/Dt • But x/t = v (velocity) • Therefore, Emf = Blv

  7. Faraday’s Law The induced emf in a coil of N loops with a changing B – field within in equal to the rate of change of magnetic flux times the number of loops.

  8. Lenz’s Law

  9. The net B-field thru a loop from a changing flux comes from two sources.

  10. The original B – field. • The B – field caused by the original current…the induced B – field.

  11. Induced B – Field This occurs because of the induced current. This can be used to determine the polarity of the induced emf.

  12. Lenz’s Law The induced emf resulting from a changing magnetic flux has a polarity that leads to an induced current whose direction is such that the induced B – field opposes the original flux change.

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