Faraday's induced emf equation

cblair

Why is there negative sign in Faraday’s induced emf equation?

rtk

"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)."

cblair

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

rtk

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.

cblair

    Thanks for clarifying.