Why are the effects off Lenz law only seen when a load is applied to a circuit? And, does Lenz law apply in a closed circuit with no load, or resistance?
2 Answers
That law can be used to predict the polarity of the induced voltage in a coil that is in a changing magnetic field. The polarity must be such way that the change in the magnetic flux would be reduced if there were a way for the current which was caused by the induced voltage.
The effect does not need resistance and it occurs also in closed circuits. For example in superconductors all changes in the magnetic flux are impossible because the induced current compensates the change.
Many sources present Lenz's law as an extended induction law. But Faraday's 2nd rule already had the absolute value of the induced emf right, so Lenz's part in the formula is the polarity.
I have not seen Lenz's nor Faraday's original writings => I cannot be sure, if Faraday possibly had some errors or holes in his concepts, so bad that Lenz can be considered to be the real inventor of the quantitative law of induction.
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\$\begingroup\$ Oh c'mon.. Lenz's law can do much more than "predicting polarity", nothing to do with the question anyway. \$\endgroup\$– carlocDec 10, 2017 at 10:11
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\$\begingroup\$ @carloc Maybe it's a little better now \$\endgroup\$– user136077Dec 10, 2017 at 11:21
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\$\begingroup\$ Original writings are very often quite obscure in up-to-date terms. They are luckily been skimmed and re-formulated as they know them today, I'd rather stuck on the latter. Back on topic, \$\nabla \times \mathbf{E} = -\partial \mathbf{B} / \partial \mathrm{t}\$ all in all. \$\endgroup\$– carlocDec 10, 2017 at 13:53
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\$\begingroup\$ @carloc all in all - except add the current density term, then I'll delete this comment. \$\endgroup\$– user136077Dec 11, 2017 at 14:45
The Lenz' law can only be applied if there is a current flowing through a wire or through whatever. This current causes a magnetic field, which interacts with surrounding magnetic fields. The interaction can be recognized by a resulting force.
The load or resistance doesn't matter, there is only current necessary. Without resistance there will no voltage drop, however this does not influence the Lenz' effect.
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\$\begingroup\$ Lenz's law does not need any current to flow. It can be applied whenever you like, you just have to imagine an integration path. If there's no or steady magnetic field it simply returns zero. Moreover, magnetic field does not imply current either, it could come from a permanent magnet. \$\endgroup\$– carlocDec 10, 2017 at 10:22