# Lenz's law and instantaneous change in inductor's current

PainterGuy
Hi,

I will use this text for my question: https://imagizer.imageshack.com/img921/1874/nUBPY6.jpg
Source: https://www.electrical4u.com/lenz-law-of-electromagnetic-induction/

The text says that when the north pole of a magnet approaches the coil, the induced current in coil is such that it creates a north pole to repel the approaching north pole of magnet. In other words, the coil resists the approach of magnet.

When the magnet's north pole starts receding from the coil, the induced current in coil is such that it creates a south pole to attract the receding north pole of magnet toward it. In other words, the coil resists the recession of magnet's north pole.

The following is my question statement. In an inductor or coil the current cannot change instantaneously. Therefore, as the magnet was approaching coil, it induced a current in the coil and this induced current generated its own magnetic field. So, when the magnetic starts receding away from coil, the current shouldn't switch its direction instantaneously. But the text suggests, or Lenz's law, as if the switch in direction of current is instantaneous. Where am I confusing it?

Delta2

Homework Helper
Gold Member
The linked text does not say things change instantaneously, and they don't.
Consider the magnet approaching the coil. For it to subsequently recede from the coil, its velocity towards the coil must continuously decrease from positive, through zero and become negative. As that happens, the current through the coil will likewise reduce to zero then grow in the opposite direction.

Hope that helps.

Last edited:
vanhees71, PainterGuy and davenn
PainterGuy
Thank you, @andrewkirk .

I think that I understand it now. There is a 180 degrees phase difference between the magnet movement and induced current. I have assumed that the magnet follows simple harmonic motion and the system has been operating for some time. Please let me know if I have it correct. Thank you.

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Homework Helper
Gold Member
Yes, given the additional assumption you state regarding the magnet's pattern of movement, that diagram agrees with my understanding of how the current reacts.

PainterGuy