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

• PainterGuy
In summary, the conversation discusses Lenz's law of electromagnetic induction and how it explains the relationship between a moving magnet and the induced current in a coil. The direction of the induced current is such that it opposes the change in magnetic field, resulting in a 180 degree phase difference between the movement of the magnet and the induced current. There is no instantaneous change and the current gradually changes as the magnet approaches and recedes from the coil.
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
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
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.

#### Attachments

• lenz_111.jpg
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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

## 1. What is Lenz's law?

Lenz's law is a fundamental law of electromagnetism that states that the direction of an induced current in a conductor will always be such that it opposes the change that caused it.

## 2. How does Lenz's law relate to Faraday's law?

Lenz's law is a consequence of Faraday's law of induction, which states that a changing magnetic field will induce an electromotive force (EMF) in a conductor. Lenz's law specifies the direction of the induced current in relation to the changing magnetic field.

## 3. What is the significance of Lenz's law?

Lenz's law is important because it helps us understand the behavior of electromagnetic phenomena, such as the production of electric current in generators and the operation of electric motors. It also helps us predict the direction of induced currents in circuits.

## 4. What is an instantaneous change in an inductor's current?

An instantaneous change in an inductor's current refers to a sudden and immediate change in the flow of electric current through an inductor. This can occur when the circuit is switched on or off, or when the current source is changed.

## 5. How does Lenz's law affect the behavior of inductors in circuits?

Lenz's law plays a crucial role in the behavior of inductors in circuits. It causes inductors to resist changes in current, creating a back EMF that opposes the applied voltage. This can result in a delay in the buildup of current in the inductor, and also causes the inductor to store energy in the form of a magnetic field.

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