Lenz's law Definition and 138 Threads

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. 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...
  2. genxium

    Voltage drop across ideal solenoidal inductor

    First by ideal I mean zero resistance. I tried to verify Faraday's law in simple LCR circuit but ran into some conflicting results. Though the description below will be a little verbose, the configuration for this problem is extremely simple: assume that I put a solenoid...
  3. L

    Induced Electric Fields: Exploring Gauss' & Lenz's Laws

    In electrostatics, ∇ × E = 0 so E that is a conservative field and there must be sources of E from which E flows. We know that this sources are the electrical charges given by Gauss' Law. But when B changes in time, ∇ × E = - ∂ B / ∂t. Now the Gauss' Law no longer applies and if there are not...
  4. K

    How does this hoverboard work?

    https://www.kickstarter.com/projects/142464853/hendo-hoverboards-worlds-first-real-hoverboard I see that it says it's based on Lenz's law, which says that the induced currents will generate a field that opposes the change in the field. So, I figure they have some kind of oscillating magnetic...
  5. D

    What Causes the Ring to Rise in Faraday's and Lenz's Law Demonstration?

    What is the actual explanation for the last demonstration, for why the ring rises up?o_O
  6. S

    ElectroMagnetics Lenz's law vs F=qv X B

    Hello and thank you in advanced for looking at this. I have trying to come to terms with two seemingly contradictory ideas in electro-magnetics. Lenze's law and Eddie currents seem to contradict the fundamental equation F = qv X B where F is the force exerted on a particle with charge q and...
  7. P

    Why do eddy currents cause oscillations to die away quickly?

    A metallic disc attached to a rod swings between two opposite magnetic poles, and its oscillation dies away very quickly. I thought this happens because the eddy currents formed inside the disc are established in a direction that would cause their magnetic field to oppose the magnetic field...
  8. O

    Will Current Flow Through a Rotating Copper Wire Loop in a Magnetic Field?

    Homework Statement A copper wire loop is initially at rest in a uniform magnetic field (full flux going through it). Between times t=t1 and t=t1+(delta)t the loop is rotated about a vertical axis as shown (no flux going through it). Will current flow through the wire of the loop during this...
  9. S

    Lenz's Law and determining direction of a current

    Hey guys, Background: I'm having trouble determining the direction of a current in a wire in response to changing magentic flux. Although I understand which direction of the magnetic field should be for the induced current given the magnetic flux scenarios, I am having trouble determining...
  10. B

    How Does Decreasing Wire Current Affect a Nearby Metal Rectangle?

    Homework Statement A metal rectangle is close to a long straight current carrying wire, with 2 sides parallel to the wire. If the current in the wire is decreasing, the rectangle is Homework Equations Lenz's Law: the direction of any magnetic induction effect is such to oppose the cause...
  11. T

    Lenz's law: determining current direction

    http://img853.imageshack.us/img853/1150/n5pj.png I a can't seem to find out how to determine the direction the current will flow in... I would really appreciate an explanation. Thanks!
  12. A

    Demagnetization of a permanent magnet and lenz's law

    this video ( ) demonstrates lenz's law, if the current produced by the magnet fall induces an opposing magnetic field , after many tries , can this field demagnetize the magnet , another thing, consider this : if the copper pipe was instead a pvc pipe, and i wrapped around it copper wires , so...
  13. A

    Calculating Force Between a Solenoid and a Cylindrical Magnet

    I've read a lot and watched a lot about lenz's law , about how a magnet moving towards a solenoid will experience an opposing force. But I tried to search how to calculate this force , found nothing . So i tried to find how to calculate force between 2 magnets . Found on wikipedia how to...
  14. A

    Lenz's law and conservation of energy

    I don't understand how lenz's law is a form of energy. An explanation said if the induced current did not oppose change, we would be obtaining energy without doing any work. I think my problem here is that I can't follow the no change -> get free energy logic.
  15. D

    Conceptual Questions Lenz's Law, Solenoid

    Homework Statement https://www.dropbox.com/s/17hsoz0zdfoston/Screen%20shot%202013-05-10%20at%2012.37.44%20PM.png 1) A voltage is applied to a solenoid such that a current is flowing in the indicated direction. Inside the solenoid is a single wire loop that is oriented in the same...
  16. P

    Lenz's law and elctromagnetic waves

    Hello, We're just starting to learn about electromagnetism and electromagnetic waves. I am still trying to grasp all these new concepts, but there's a question that's bugging me. From what I understood an alternating magnetic field will generate an alternating electric field which in turn...
  17. K

    Lenz's law - magnetic fields and Currents

    Hey Pf.. I am trying to understand Lenz's law, but somehow it doesn't make sense. In my book there is some checkpoints execise to test wheather you've understood what you read about, one those checkpoints looks like this. http://snag.gy/NCNLh.jpg I do understand why the current in...
  18. Ackbach

    MHB Confusing Issue with Lenz's Law

    In my AP Physics B class that I'm teaching, we arrived at Lenz's Law, and had difficulty with Conceptual Example 21-4 (e), located on page 588 of Giancoli's Physics, 6th Ed., which goes like this: A closed conducting circle of wire is lying the plane of the page (or screen), and there is a...
  19. 0

    How Does Lenz's Law Explain the Interaction of Magnetic Fields in Inductors?

    The Law: The direction of the induced current creates an induced magnetic field that opposes the motion of the inducing magnetic field. Application: When the north pole of a magnet goes INTO a solenoid, the opening where the magnet is entering from becomes South. As it exits, the same opening...
  20. 0

    What is Lenz's Law of Electromotive Forces and How Does It Work?

    I'm in grade 12 physics trying to understand how motors work. My teacher is useless. I read the official law, but I do not understand how it conceptually works. Here is the aplet he gave me, if you want to explain with respect to a visual...
  21. C

    Lenz's law for point charge in time varying magnetic field?

    Hello friends, So I have a point charge with mass m and charge +e entering a uniform magnetic field B at velocity v from the "right". The field is perp to the velocity pointing "in", so I see that eventually this particle reaches a steady state of uniform circular motion (counter clockwise)...
  22. D

    Simple problem on Lenz's Law application using Right Hand Rule

    Hi everyone! I'm trying to work out a physics problem using Lenz's Law, but I'm having trouble with the Right Hand rule, which as I understand is supposed to be used to solve the problem. 1. Basically, there are 2 copper wire loops, Loop A and Loop B. They are lying flat on the table. There...
  23. B

    The affects of Lenz's Law on Wind Turbines

    Hi, If an electrical generator induces a current that opposes the shifting magnetic field that creates it then why don't the wind turbines on wind farms just stop turning after a while? Is it because they are not directly connected or drawn on by electrical devices? Thank you all in advance!
  24. E

    Relating the lenz's law which is making me crazy

    Hello there.. Lenz's law has driven me crazy for many days.. I need to settle an end for this so i would actually give my doubt hoping for a good reply... Now, in many sites I've seen that the flux can actually as they say "INCREASE"" ... How is it even possible if the flux in any form is CUT...
  25. C

    What Experiments Can Test Lenz's Law in a Year 12 Physics EEI?

    Hi, This is my first post here and I have attempted to post in the right section, if I haven't, please excuse me. I am doing a year 12 physics EEI about Lenz's law, but I am a bit confused about what I can experiment and what variables I can use to make my experiment 'complex and...
  26. T

    Motional emf, Gaussian flux, and lenz's law help

    Homework Statement Two bars, each 30cm long, and each having a resistance of 2-ohms, are connected to a 1,500 volt battery. The bars are attached to each other with 3 insulating springs, each having a spring constant of 9N/m. The two bars are initially at rest, 4cm apart. The switch is...
  27. L

    Quick Conceptual Question on Lenz's Law

    Homework Statement A magnetic field is uniform throughout a region of space, but increases from 0 to 0.14 T in 2.4 s. A circular coil (of diameter 19 cm) is placed in a fixed orientation in this region such as to receive maximum flux. It takes 4171.91 turns to generate an emf of 6.9 V What...
  28. S

    Lenz's Law and Law of Conservation of Energy

    Hi How does Lenz's law obey the Law of Energy Conservation? I know it has to but I really don't get it. Thanks Salil
  29. C

    Having a really hard time understanding Lenz's Law

    I have read my text and watched youtube videos but this just won't register in my brain. Does anyone have a much simpler way to explain it or know of another source that can help. Specifically, how would one use it to figure out the direction a current is going given a variety of different...
  30. W

    How Does Lenz's Law Determine Current Direction in Moving Magnets and Solenoids?

    Homework Statement Hi. My questions are on Lenz's Law. 1. We have a bar magnet indicated by the [N | S]. It is moving to the left of a solenoid that is connected to an ammeter. Two points on the circuit are labelled X and Y. ( A ) is just an ammeter. The question is.. What direction does the...
  31. B

    Question on Faraday's and Lenz's Law

    Homework Statement http://imageshack.us/photo/my-images/16/snipu.jpg/ Homework Equations The Attempt at a Solution The magnetic field in the bar magnet is directed to the right, but weakening in magnitude because the magnet is being moved far away from the loop. So by Lenz's...
  32. T

    Does the converse of Lenz's Law act to compensate for E flux?

    Lenz's Law says that the induced emf from a change in B flux creates a B field that compensates for the flux change. I know that a changing E field induces a magnetic field as well, but does that magnetic field act in a way to compensate for the change in the E field? Or is that not physically...
  33. M

    Why Does Lenz's Law Induce a Clockwise Current When a Bar Moves Right?

    The bar in figure Q31.5 moves on rails to the right with a velocity, v, and the uniform, constant magnetic field is directed out of the page. Why is the induced current clockwise? If the bar were moving to the left, what would be the direction of the induced current? (The figure is at the...
  34. A

    Help with Lenz's Law Homework - Right Hand Rule and Magnetic Field Direction

    Homework Statement Please click on the following link for the question. http://i1008.photobucket.com/albums/af204/John132456/physics.jpg Homework Equations Lenz's law. This states that when emf produces current, the magnetic field will oppose change. The Attempt at a Solution...
  35. P

    What happens when you drop magnets in aluminum and glass tubes simultaneously?

    Dropping a strong magnet in an aluminum tube is cool, but what will happen if magnets are dropped at the same time in tubes of aluminum and glass that are adjacent? Or at a defined distance due to strength of the magnets? Somebody probably has thought of this and demonstrated the results. It...
  36. L

    Lenz's law - some doubts in this

    Lenz's law -- some doubts in this Homework Statement Dear members, Please refer my attachment lenz law When the bar magnet with its N-pole is moved towards the coil, the induced current produced in coil S opposes the motion of magnet. It will happen so, if the induced current in the coil S...
  37. K

    Question about Lenz's Law: Is It Always Opposite?

    I have a question regarding Lenz's Law. In many of the passages that I read about Lenz's Law, I see this: "If the magnetic field of current i1 induces another current, i2, the direction of i2 is opposite that of i1." I don't think this is always true, though. For example, let's assume we have...
  38. J

    Finding induced current (Lenz's Law)

    Homework Statement Attached below Homework Equations Emf = - \Delta\Phi / \Deltat emf = vBl; motional emf The Attempt at a Solution In the two attached files, there are problems that ask for the direction of the induced current. I understand that the induced current flows in the...
  39. X

    The Meissner Effect & Lenz's Law

    Hi, I am quite confused about how the Meissner Effect works. I know that below the critical temperature of a superconductor, it will exclude all magnetic fields going through it. But why is this so? And I also know that as a magnet is brought near the surface of a cooled superconductor...
  40. N

    Basic Lenz's Law question, loop near current carrying wire

    So I need to study Lenz's law and have only learned the absolute basics so far. I'm a little stuck on this study question. I'd really appreciate anyone who helps solidify my understanding of it a little bit! Homework Statement Consider a circular loop of wire near a long...
  41. F

    How can I quickly determine the direction of induced current using Lenz's Law?

    Homework Statement http://img863.imageshack.us/i/circuitsigh.png/ Uploaded with ImageShack.us The Attempt at a Solution Alright in the picture you see two hands (YES THEY ARE HANDS). The one my book says is to use your palm and let your palm be opposite to v and other fingers...
  42. J

    Right Hand Rule for Lenz's Law: Examples & Solutions

    Homework Statement I am having trouble understanding right hand rule for Lenz's Law. I need to know how to use the right hand rule with lenz'z law to find the dircection of induced current. What if a current is flowing clockwise, with mag. field going into page, is the magnetic field...
  43. J

    How Does Lenz's Law Explain the Movement of a Loop Near a Current-Carrying Wire?

    Homework Statement The diagram below shows two circuits: a very long straight wire, and a single loop rectangle of dimensions a and b. The rectangle lies in a plane through the wire and is placed a distance c from the long wire as shown. The long straight wire carries a current of I...
  44. J

    Lenz's Law and conservation of energy.

    Hello everyone, first time posting in here. Heres a question, in Lenz's Law, it states that the current produced will be opposite of the motion that created it. This is done by the repulsion or attraction force created by the solenoid to counter the motion of the magnet. Now, without the work...
  45. F

    Lenz's Law and Energy Conservation

    how does the lenzs law relates to the law of coservation of energy ?
  46. D

    Magnet in copper tube lab calculations (Lenz's Law)

    Homework Statement a magnet that weighs 2.6 grams is dropped through a 1.53 metre tube. the average time taken for it to go through is 1.59 seconds. I need to find the strength of the magnetic field and the currentHomework Equations Fg=mg B=F/IlsinthetaThe Attempt at a Solution...
  47. E

    Eddy Currents: Understanding Lenz's Law

    I don't really understand what is eddy current. Is it just the current that is formed using Lenz's law? Or is it different? My idea of eddy current is that it is of many small swirls all over a metal plate that opposes the force exerted to move the plate. Thank you.
  48. M

    Where Does Lenz's Law Apply in an Automotive Setting?

    A bar magnet is dropped from rest through the centre of a coil of wire which is connected to a resistor and datalogger. The resistor and datalogger are to the left in the diagram, and the coil on the right side. Add an arrow to the wire to show the direction of the induced current as the...
  49. C

    Explaining Eddy Currents in Maglev & Levitation Expts

    Can someone explain the role of eddy currents that produce levitation such as in the floating tube expt or the jumping ring? How is the jumping ring altered to achieve stability? i.e raising the ring a fixed distance above the coil? Like in maglev transportation...or is it just dependant on the...
  50. D

    Lenz's Law: Direction of Flux & Current

    Homework Statement I don't have the question with me, it was on a test I did. It was something like this though: A coil is placed vertically on a table. The magnetic field there is also vertical. If the magnetic field is suddenly switched off, in which direction would the current in the...
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