In case of earthing, we attach a single wire to the earth and if some residual electrons remain in the instrument they flow to the earth until the potential of the instrument also becomes Zero. So if I have an open circuit in the form of a partial loop and I place it in changing magnetic field, then according to Faraday's law emf will be induced in it and hence some potential difference develops so why does current not flow through that open circuit?
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$\begingroup$ Because a ground connection is not an open circuit. $\endgroup$– Jon CusterCommented Jun 11, 2023 at 3:24
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1$\begingroup$ An antenna that is not connected to anything still has currents sloshing back and forth. $\endgroup$– Jon CusterCommented Jun 11, 2023 at 3:36
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$\begingroup$ Displacement current flows through capacitors just fine. The real problem is that we teach electrostatics and magnetostatics, which are both approximations of electrodynamics, first. This makes electrodynamics appear somewhat "magical" for the student. In reality it's the other way around: the only (mostly) self-consistent physics is that of classical electrodynamics. It's just too complicated to explain it in detail to the beginner. Educational needs often trump scientific logic. $\endgroup$– FlatterMannCommented Jun 11, 2023 at 3:47
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2 Answers
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Saying an emf is induced in a wire is really saying that an electric field is induced within that wire. This field will cause electrons to move within the wire (because it is a conductor) into a configuration in which the electric field within the wire is zero.
If the changing magnetic field is oscillating then the induced electric field will keep changing, so the electrons will keep moving around to try to keep a zero electric field in the wire.
This is not really a current in a circuit, because a partial loop is not usually a complete circuit. There are exceptions though. The partial loop can be analysed as a circuit if you regard the two unconnected ends and the space between then as forming a capacitor. And if the induced electric field between the ends is strong enough the air between them will become a conductor. In this case you may see the arc joining the two ends though the air.
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A changing magnetic field always induces currents in a metal. The free-moving electrons are moved in one direction and an area with an excess of electrons and an area with a shortage of electrons is created in the conductor. See the Hall effects.
For an open conductor, this induction naturally has its limits. As the excess/deficiency of electrons increases, the electric potential at the ends of the conductor becomes stronger and the swelling magnetic field becomes more and more inefficient. But since we often use an oscillating magnetic field, the electrons are moved back and forth from one side of the conductor to the other. What we get there, by the way, is a magnetic loop antenna.
answered Jun 12, 2023 at 4:35