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In the typical youtube animations/drawings of the electric and magnetic field fluctuations, the magnetic field peaks at the same time the electric field peaks. Since a magnetic field is created with a “changing” electric field, shouldnt the magnetic field peak when the electric field is changing most rapidly, namely, when the electric field is crossing from positive to negative? As the animations show, the magnetic field is peaked when the electric field is slowing to a stop then changing direction, and this doesnt seem correct to me. Are these animations just simplifying the actual dynamic?

Edit: so if dB/dt = dE/dt, a change in electric field causes a CHANGE in magnetic field? So when change of electric field is zero the change in magnetic field is zero?

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  • $\begingroup$ They’re not shifted by 90 degrees, as you might expect, and you can see this from Maxwell’s equations. What you say would be true if B were equal to a first derivative of E. But instead, a first derivative of B is equal to a first derivative of E, so they are in phase. $\endgroup$
    – knzhou
    Commented Aug 4, 2018 at 9:18
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    $\begingroup$ I have tried to answer your question with the minimum of mathematics here physics.stackexchange.com/q/4071 $\endgroup$
    – Farcher
    Commented Aug 4, 2018 at 9:25

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