In the early 1830’s, Michael Faraday and Joseph Henry independently discovered the relationship between changing magnetic fields and induced EMF in circuits. If B is the flux density of a constant magnetic field and a conductor is moved through this field at a velocity V, an EMF E is generated in the conductor such that:
E=BxV
If the conductor is part of a complete electrical circuit with a resistance R, then the EMF will produce a current in the conductor such that:
I = E / R = B x V / R
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| Figure 1 |
The development of an EMF in a conductor moving in a magnetic field is the principle on which many types of tachometers are based. By using the commutation techniques described in the next section, a rotary device can be constructed which has, as its input, a rotary mechanical motion and, as its output, a voltage proportional to that input rotational velocity.
Another specific application of Faraday’s Law is used in electric motors. That is, if a conductor of length L carrying a current I is placed in a magnetic field B, a magnetic force F is created such that:
F = BLI sin A
where A is the included angle between B and I.
The force vector F is a vector perpendicular to both vector quantities B and I.
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| Figure 2 |
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