What is Lenz's law: Definition and 137 Discussions

Lenz's law, named after the physicist Emil Lenz (pronounced ) who formulated it in 1834, states that the direction of the electric current which is induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field.
It is a qualitative law that specifies the direction of induced current, but states nothing about its magnitude. Lenz's law predicts the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or the drag force of eddy currents exerted on moving objects in a magnetic field.
Lenz's law may be seen as analogous to Newton's third law in classical mechanics.

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  1. Z

    Origin of repulsive force on a magnet approaching conducting ring?

    Between ##t_1## and ##t_2## the magnetic flux is positive and increasing. Thus, we have a negative emf and from the point of view of the little stick figure above, the induced current is clockwise. It is not clear to me where the repulsive force on the approaching magnet comes from. The...
  2. Z

    What is the induced magnetic force on this closed current loop?

    Below I will go through derivations I saw in some notes from MIT OCW's 8.02 "Electricity and Magnetism". We thus have a closed loop. Let the normal vector be ##\hat{n}=\hat{k}##. Then, the area vector is ##\vec{A}=A\hat{k}##. The magnetic flux through this loop is...
  3. hongseok

    I Does Diamagnetism Occur Even in a Constant Magnetic Field?

    I learned that diamagnetism is due to Lenz's law. But doesn't Lenz's law only apply when the magnetic field changes? Why does diamagnetism occur even when a constant magnetic field is applied without change?
  4. P

    Qualitative explanation of Magnetic Braking

    When a magnet moves near a non-magnetic conductor such as copper and aluminium, it experiences a dissipative force called magnetic braking force. I am rather confused by the following explanation of magnetic braking force: The non-magnetic conductor here is the aluminium 'wall' seen on the...
  5. waazwag

    Induced voltage difference in a magnetic field

    Hi everyone, I'm currently working on the problem listed above. I'm pretty new to electrodynamics, and I'm learning on my own through a book. I was wondering if someone can please help me through this problem. Here are my thoughts:I think I need to use Faraday's Law of Induction for part (a)...
  6. K

    EMF shielding using a conductor

    So I've been trying to figure out how EMF shielding works. More specifically, I've seen videos where placing a metal conductor in front of a circular coil (with AC running through at radio frequencies) apparently shielded anything behind it. After searching online, I repeatedly saw Eddy...
  7. PainterGuy

    Induction motor and Lenz's law

    Hi, The shown below, Figure 1, is an interaction of magnetic fields of stator and rotor of a squirrel cage induction motor. I believe the current is coming out of the squirrel cage bar on the left and entering on the right as is shown below, Figure 2. I have assumed that the bars highlighted in...
  8. PainterGuy

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

    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...
  9. N

    Lenz's Law for a rotating PM motor rotor spinning in a thin CU tube

    The motor is required to operate at its resonance frequency and I am looking to add a thin-walled (0.010") copper tube inside the stator bore to add some damping. The current motor air-gap is 0.015". If I install a copper tube in the stator bore bonded to the stator and leave a 0.005" air-gap...
  10. S

    Lenz's law: Current induced in a split loop by a changing B-field

    Homework Statement We have a circular loop of wire, with AB is another wire which is also the diameter of the circular loop. The direction of magnetic field is perpendicular to the loop, into the plane of paper. The magnetic field strength is decreased at a constant rate, without changing the...
  11. H

    Find induced current, magnetic force, work in inclined plane

    Homework Statement [IMG]http://[url=https://ibb.co/b3Emfo]https://preview.ibb.co/gLaEY8/20180527_055248.jpg[ A conducting bar slides down without friction on a pair of conducting rails separated by distance d. Connected to resistor R and there magnetic field B directed upward, perpendicular to...
  12. Dustin

    B 4 Questions About Lenz's Law Experiment

    Hello, I have four questions. As it stands now, I don't have the necessary materials to test this myself, which is how I'd prefer to learn the answer. I still plan on doing this experiment for fun once I can acquire the necessary components. This deals with Lenz's Law. My goal is to maximize...
  13. C

    What is the direction of the current in the given image?

    Homework Statement In the picture 20.40, what is the direction of the current induced in the resistor at the instant the switch is closed.[/B]Homework Equations Right hand rules- Point thumb in direction of current and your fingers will curl in direction of magnetic field. Lenz's law. The...
  14. VSayantan

    Speed of a Magnet Falling through a Conducting Wire

    Homework Statement A small but very powerful bar magnet falls from rest under gravity through the center of a horizontal ring of conducting wire, as shown in the figure below (on the left). The speed-versus-time graph, in arbitrary units, of the magnet will correspond most closely to which of...
  15. Marcin H

    Lenz's Law and Faraday's Law clarification

    Homework Statement This isn't a problem, but I wanted to get some clarification of Lenz's law and Faradays law. So if you have a solenoid of wiresand you take a magnet and move it through the solenoid with a velocity v that magnet will induce a current into the wire according to the right hand...
  16. B

    Magnetic Flux Questions from Japanese University Exam Papers

    Hello everyone, This is my first post here Firstly, I'd like to start by saying that it's my best intention to follow the rules on this forum. Therefore, if I've posted this in the wrong section please forgive me, I will try and learn the ropes quickly. One of my students has given me some...
  17. S

    Exploring Eddy Currents & Lenz's Law

    Homework Statement In one of the most common examples of Lenz's Law a magnet is dropped inside a copper tube and due the induced emf and the eddy currents generated in the copper tube the magnet falls through it with constant velocity. The external force that the eddy currents oppose is...
  18. Y

    What force does the current carrying coil feel?

    Homework Statement What direction does the force that the current carrying coil feel point to when a magnetic field is turned on? A magnetic field is turned on and points from bottom to top and passes through a current carrying coil that has current passing through it CCW. Here is a diagram...
  19. J

    Lenz's Law and Induced Magnetic Fields

    In a transformer, the primary coil has a current running through it which creates a magnetic field. Then this field induces a current in the secondary coil. That induced current creates a magnetic field exactly opposite the inducing magnetic field. This might be an obvious question, but that...
  20. M

    How does Lenz's law delay coil field collapse in magnetos?

    Perhaps the title of this post is not quite correct because I could not find a way to abbreviate what I am asking. Picture a magneto circuit, where, an alternator is used to generate an AC flux into a primary coil of a ignition coil by means of a magnetic core (the primary is wrapped around the...
  21. G

    Ballistic Lenz's Law: Magnet Induced Current in Copper Tube

    If a magnet was going fast enough as it approached/entered a copper tube, could the current induced in the tube via Lenz's Law be high enough to melt or even vaporize the tube?
  22. G

    Textbook picture: Is direction of this eddy current wrong?

    Hi. This is from a high school textbook, in a chapter about eddy currents and Lenz's law. In a), a magnetic field is turned on, in b) it's turned off, which both induces a current in a suspended aluminium ring: I think the direction of the current is wrong in both pictures. Any opinions?
  23. AaromTheBritt

    I Remembering Lenz's Law: An Easier Way?

    I'm working on induction at the moment, and the math makes sense, but Lenz's Law is giving me trouble. Does anyone have an easier way (relatively) of remembering the directions of emf? Any advice is appreciated.
  24. C

    B Lenz's law questions from a dad of a smart son

    if this is in the wrong place, i apologize. you guys helped me out before so i was able to not sound like an idiot to my son and helped us share time and interests together this year in 6th grade he did a great science fair project on the duality of light and did the double slit experiment and...
  25. M

    Lenz's Law in action with different length magnets

    Hi, I was doing an experiment with Neodymium magnets and a long copper pipe (3cm internal diameter) to see Lenz's Law in action. At first I used a long bar magnet (about 15cm long) and there was little resistance to the magnet falling through the pipe. It was only slightly slower than a...
  26. Biker

    Magnetic induction: Lenz's law

    Homework Statement After you close the switch, There will be an induced current in the resistance R, Choose one of the following: Direction of current ... magnitude of current A to B ... decreasing A to B ... increasing B to A decreasing B to A... Increasing Homework Equations Faraday's law...
  27. M

    Faraday's and Lenz law - Experiment with AC coil and Cu ring

    Hi, can someone explain me the next experiment: If I have an AC coil on iron stick, and if I put Cu ring on that stick concentric with AC coil, when I turn coil power supply, the ring will levitate on some height. My question is: Powered AC coil produces an AC magnetic field. If I put a...
  28. P

    Need help understanding Lenz's Law

    Homework Statement I'm trying to find the direction of the current given certain situations, but do not know how to apply Lenz's Law. Attached a image below- 2. The attempt at a solution So I figured out how each situation affects the induced current, and that the magnetic field is to the...
  29. Astik

    How are Lenz's law and Faraday's law connected?

    I want to know the angle of view from which Lenz's law and Faraday's law can be seen methodically.
  30. Narayanan KR

    A motor design to defy Lenz' law?

    1. The two rotors (purple, green) are electricaly isolated but mechanically fit to rotate along same axis 2. The motor action on the left side rotor will move the armature set, this will produce currents in right side rotor that will pass via a variable load. 3. do you see the magnetic fields...
  31. Rmehtany

    Understanding Lenz's Law and the Right Hand Rule in Electromagnetic Induction

    Homework Statement Homework Equations Not really? I just used the right hand rule and Lenz's law The Attempt at a Solution By the right hand rule, outside of loop 1, the magnetic field is out of the page. However, increasing resistance means that field is weakening. We know by Lenz's law...
  32. B

    Is Current I1 Constant in Mutual Inductance Systems?

    Hello, Homework Statement All variables and known data are given in one of the attached files. Does the figure 8.2 show that the current I1 is constant? My assumption is based on Lenz's law. What I mean is that if the I1 varies, there will be changes in magnetic fluxes(delta-B) produced by...
  33. kostoglotov

    Lenz's Law applied to a non-circuit conductor?

    I was reading through my College Physics text, and it talked about how NASA once swung a 20km long conductor through the Earth's magnetic field and setup a 3500V potential difference along the wire. I understand that there's no conventional current in that wire, it's not a circuit. But for a...
  34. M

    [Magnetic Flux and Lenz's Law] Is this picture correct?

    Is the arrow of the ammeter pointing in the correct direction? The induced current is going through the positive end of the ammeter and out of the negative end. Since current is traveling towards the positive end of the ammeter, shouldn't the ammeter point towards the negative direction?
  35. A

    Exploring Lenz's Law: A High Schooler's Guide

    Hello everybody, I am a senior in high school and I was wondering if anybody could help me with Lenz's Law .. I was wondering if there is a specific demonstration for this law or if just connected with Faraday-Neumann law demonstration because for what I have seen in my book there isn't a...
  36. A

    Understanding Lenz's Law: Impediments to Electromagnetic Induction

    Hello to all, Is the electromagnetic induction impeded by Lenz's law? Is this why the generators must have a minimum RPM? Is there any way to go around it? My motivation for the question resides in my being a philosopher of science. That means that I dabble in pretty much anything that science...
  37. L

    Why is the negative sign in the equation for motional EMF often discarded?

    I'm trying to understand how electric generators work on a very basic level. I understand the heart of this is the application of the Lorentz force on a conductor moving at a velocity ##v## in the presence of a magnetic field ##B##. I also understand how it can be shown that the emf is equal to...
  38. L

    Lenz's Law Q: Clockwise or Counterclockwise?

    Homework Statement A long, straight wire lies on a table and carries a current I. As the drawing shows, a small circular loop of wire is pushed across the top of the table from position 1 to position 2. Determine the direction of the induced current, clockwise or counterclockwise, as the loop...
  39. Kerrigoth

    Are induced currents created by motion or change in flux?

    The book I am working through is beginning to dive into induced currents and Lenz's Law. When a conductor is moving perpendicular to a magnetic field, the charge carriers inside will experience a magnetic force; This causes the charges to move. Eventually, the electric field from the charge...
  40. S

    Understanding the Negative Sign in Lenz's Law: A Geometric Interpretation

    Homework Statement I'm trying to see the relationship between the negative sign (Lenz's Law) in Faraday's law. It states that EMF is equal to negative flux change. I understand how to use Lenz's Law to find direction of current and hence EMF, but I am not seeing the relation between the neg...
  41. F

    Force on a Magnet in Lenz's Law

    Homework Statement As the bar magnet (see attached diagram) leaves the loop of wire, it experiences a force opposing its exit. I understand why, according to Lenz's law, a force would oppose the bar magnet's exit. I don't understand, however, what causes the force. In this case, the force is...
  42. M

    Magnetic Levitation : Confusion with Lenz's Law

    Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an alternating current, an alternating magnetic field is produced, similar to a sine wave. Therefore, I...
  43. 2

    Back emf in a single loop of wire?

    I have been thinking about coils of wire carrying alternatingcurrent. From what I understand, a back emf is induced in the coil because there is a changing magnetic field around each individual loop of wire, and therefore there is a changing flux through each loop because the changing field...
  44. jbenson

    Ampere's Law & Faraday's Law: Exploring Electromagnetic Wave

    First, some background. In Faraday's law the reluctance/resistance by "mother nature" to changing the magnetic flux is explicitly recognized by the "-" sign (commonly referred to as Lenz's law), i.e. if the time rate of change of the magnetic flux is positive, an emf is induced so as to oppose...
  45. G

    Exploring the Effects of Magnet Size on Lenz's Law

    In all demonstrations of Lenz's Law that I've seen about the falling magnet, the diameter of the magnet is roughly the same size as that of the tube. Would there be any difference if the magnet was significantly smaller?
  46. cseil

    Faraday's and Lenz's Law - square coil

    Homework Statement A square coil rotates around an axis passing through the center. It is inside a magnetic field of B= 0.6T uniform and constant. The side of the coil is a = 2cm, the resistance R is 0.1 ohm. The coil is powered by a generator that gives an emf = 0.2 + 0.24sin(ωt). The current...
  47. G

    Exploring the Effects of Multiple Tubes on Induced Current in Lenz's Law

    Obviously if a magnet falls down a conducting tube, it induces a current in the tube. But what if you surrounded the tube with other identical tubes in parallel with the first one so that they're touching, and then wrapped wire around those other tubes? Would the current induced in the wrapped...
  48. cseil

    Faraday's and Lenz's law application

    Homework Statement A rectangular coil with a and b sides can rotate around the axis AA' with angular velocity ω. It is in a magnetic field as in figure. Calculate the flux of B when the coil is orthogonal to the axis AA'. Calculate the \epsilon_{max} and express the position of the coil...