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Consider the following image.

Mutual Inductance

When the battery is connected then current starts flowing through the primary cicuit and magnetic flux changes through the coil, this causes electricity to be induced in the secondary coil. Now from Lenz's law, we know that the induced current in the secondary coil would flow in such a way so as to oppose the magnetic field created by the primary coil and thus there is a slight decrease in the flux through the primary coil which would in turn increase the emf across the primary coil and thus create higher amount of electricity . Where is the flaw in my argument ?

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  • $\begingroup$ When the first field turns on, there is a large change in the flux and so a large opposing field is created in the secondary coil. However, when the induced field in the primary coil is created, it is not nearly as large as the original field, so the change in flux of through the secondary coil is significantly smaller. The net effect of each successive induced field is that the secondary coil produces declining amounts of opposing current. $\endgroup$ – Jim Feb 6 '15 at 16:23
  • $\begingroup$ The initial induced current in the secondary is not persistent because the original field from the primary is no longer changing (only the much smaller induced fields in the primary are changing). No change in the original field means the original induced secondary currents cease, so the result is not cumulative, but diminishing induced currents $\endgroup$ – Jim Feb 6 '15 at 16:25
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What you describe essentially happens in superconductors. There "perpetual electricity" exists in the form of super currents. In normal inductors, though, the resistance of the conductor steadily dissipates the current leading to field collapse.

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The wrong way of thinking: The oposite flux of secondary coil induces "additional" emf in the primary coil which increases the current in the primary coil. The correct way of thinking: The oposite flux of secondary coil decreases the flux in primary coil, hence a lower current is necessary in the primary coil to create the decreased flux. To be more clear, the lower current in the primary coil means higher resistance (reactance) of this coil, so the secondary circuit with a secondary resistor can be seen as a resistor somehow (via coils) added in serie to the primary circuit.

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