According to Faraday's law,a necessary and sufficient condition for an electromotive force to be induced in a closed circuit loop is the presence in the loop of

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Faraday's law states that an electromotive force (EMF) is induced in a closed circuit loop when there is a time-varying magnetic flux passing through the surface enclosed by the loop. Therefore, the necessary and sufficient condition for EMF induction is a time-varying magnetic flux. Choice A is incorrect because a magnetic field alone does not induce an EMF, it must be a time-varying magnetic flux. Choice B is not necessary for EMF induction, as the presence of magnetic materials does not guarantee a time-varying magnetic flux. Choice C is incorrect because an electric current in the loop does not by itself induce an EMF. Choice E is partially correct because a time-varying magnetic field can induce a time-varying magnetic flux and therefore an EMF, but a time-varying magnetic flux alone is sufficient.

According to Faraday's Law,a Necessary and Sufficient Condition for an Electromotive