Faraday's induced emf equation

cblaircblair Forum Coordinator Posts: 0
Why is there negative sign in Faraday’s induced emf equation?


  • rtkrtk Pune, IndiaPosts: 167Forum Coordinator

    "Faraday’s laws of electromagnetic induction states that when a coil of wire is placed in a changing magnetic field (B) an EMF (E) is induced in the coil and the induced EMF is proportional to the rate of change of flux linkage with the coil (dφ/dt).

    E = N(- dφ/dt)

    Meaning of the minus sign in Faraday’s law is explained by Lenz’s law which says if the B field changes, the voltage induced in the coil will try to drive a current that produces a B-field which opposes the change(in primary B field)."

  • cblaircblair Posts: 102Forum Coordinator

    Thanks, Could you please elaborate more on what does the negative sign signify?

  • rtkrtk Pune, IndiaPosts: 167Forum Coordinator
    Hi - The minus sign in Faraday’s induced emf equation signifies that when decreasing the B (negative dΦ/dt) causes positive voltage, which boosts B in the coil and when increasing the B (positive dΦ/dt) causes negative voltage, which reduces B in the coil. If the induced voltage aids the change in B-field, that would induce more voltage, further changing the B-field, which induces more voltage, further changing the B field causing a never-ending loop of infinite current and B-field. Simply to say the negative sign signifies that field and energy will remain finite.
  • cblaircblair Posts: 102Forum Coordinator
        Thanks for clarifying.
  • MdShamimAhmedMdShamimAhmed Posts: 1Member

    I need to use some verification sample in ANSYS to calculate generated voltage based on Faraday laws. Which verification sample  did I select for ANSYS?

  • ChadCapoteChadCapote Posts: 6Member
    edited December 2021

    This PDF - Understanding and using the minus sign in Faraday's law, explains everything you need - the negative sign in faraday's law, Lenz's law, and application of the negative sign in Faraday's law. Additionally, you can also read Engineering Electromagnetics by William Hayt - this would give you an excellent insight into the world of electromagnetics and its application in major science.

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