# What is Lenz law: Definition + 25 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. ### How does an eddy current brake work exactly?

I read this explanation on the Wikipedia entry for "eddy current brake". Let me go through the reasoning there. We have the metal sheet ##C## moving to the right under the magnet. For the parts of the sheet moving toward the magnet, the magnetic flux from the magnet is increasing. From...
2. ### Lenz law how to find dA/dT and O?

Hello, I am new and I have a question about the lenz law. How I am suppose to find DA/dt and o in this problem? A= 9 but D(9)/dt is equal to 0 ? And I don't really know what is the angle o means in this formula. If I found the voltage i can find the current with I= eps/Req .
3. ### Direction of current in smaller loop on the left and on the right

Lets say the current in the larger loop is counterclockwise. Then it doesn't matter if the smaller loop is to the right or to the left of the larger one, the induced current in it will always be clockwise. The magnetic field due to the smaller loop current always points in the negative...
4. ### Induced EMF in closed loops around bar magnet

I wonder if there is a way to calculate induced EMF in closed loops around bar magnet, which is traveling with constant velocity v to the right as depicted?
5. ### 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...
6. ### Need explanation about magnetic forces

Hi, I saw this video and I can't explain why the magnet is propelled to the end of the coil with such a huge force. Can someone explain it in clear terms. I also tried to use Flemings left hand (or right hand) rule but it did not give me a satisfactory answer. Thanks, SM
7. ### 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...
8. ### Dynamo design with regenerative back mmf

In the above presented dynamo design, three snapshots taken during three instances during the rotor running. In fig 1 the approaching magnet builds an induced voltage across the coil, however the circuit is still open, hence no current flows. In fig 2 when the rotor reaches TDC (top...
9. ### 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...
10. ### Inductors' voltage direction and Lenz Law

In the attached figure, a de-energizing RL circuit is drawn (left switch is opened while right switch is closed). In the drawing the voltage induced in the inductor is put to be negative so that the math works out. However, that would be against Lenz's law, wouldn't it? The inductor should be...
11. ### Understanding Lenz Law: Impact on Current Direction in a Magnetic Field

So say you have a square loop of wire which has a current of some positive value going clockwise and it enters a magnetic field going into the board. Now since lenz law states that the induced emf will make a current going counterclockwise (to oppose changing mag flux) then what is the new...
12. ### Lenz Law copper tube problem modification

Homework Statement If we drop a bar magnet down a copper tube, it will travel down very slowly. If we now cut vertical slits in the copper tube, will the magnet travel down faster or slower as compared to the original problem? Homework Equations \int \vec E \cdot d \vec l = -\frac{d...
13. ### Ideal Transformers and Lenz Law

Hi, Can somebody answer this question? The induced magnetic field of the secondary coil opposes the magnetic field of the primary. Therefore there is a lower magnetic field on the primary - lower impedance and a lower voltage drop. This results in an increased primary current which will...
14. ### Understanding Lenz Law: How Current Flows in Close Proximity Coils

Homework Statement Figure shows two coils placed close to each other . When the key is pressed so that a current starts building up in one the coils (a) a current flows along CBA in the loop (b) a current flows along ABC in the loop (c) No current flows through the loop (d) An...
15. ### Faraday Lenz law are just getting me more confused

I am sick of searching and being confused more and more specially about lenz law... THere are many demonstrations and many law.. Can someone list atleast the most important one...
16. ### Lenz law wire and expanding loop

Lenz law problem wire and expanding loop Homework Statement The loop has current radius R the red bar moves at velocity V. The distance the wire is from the loop is d and the top of the loop is length l Find the induced emf and the direction of the current in the loop. Homework Equations...
17. ### Exploring the Reversal of Lenz Law: What Would Happen?

Question about Lenz Law. When a magnet is moved towards a coil, it produces a current in the coil. The current flows in the coil in the direction which produces an "induced" magnetic field that pushes away the motion of the approaching magnet. Faster the magnet approaches, bigger the current...
18. ### Discussion of Faradays and Lenz law.

This started in the MIT professor's thread. But this part is concentrated on Faradays and Lenz law in constant magnetic flux loop and transformer that is very interesting and not quite relate to the MIT professor discussion. I want to bring this out and continue discussion about the Faraday's...
19. ### How do Lenz's Law and the right hand rule work together in electromagnetism?

I am having trouble understanding how the right hand rule works with lenz's law. Please explain
20. ### Lenz Law in a single-phase pulsed induction generator

Hello. I have made a little generator which is running quite efficiently but i would like to see if i can squeeze one or two percent more out of it. My physics knowledge is very poor and i wonder if anyone could tell me how Lenz's Law is affecting the device. I will describe it then attach...
21. ### Lenz Law: Which Capacitor Plate Becomes Positive?

A circuit contains a resistor and an uncharged capacitor. Pointing into the plane of the circuit is a uniform magnetic field (B). If the magnetic field increases in magnitude with time, which plate of the capacitor (top or bottom) becomes positively charged? I don't understand how the...
22. ### Does Lenz's Law Apply When Inserting an Iron Rod in a Solenoid?

1. suppose a long solenoid is connected to a DC source and after a long time steady state has reached. And suddenly an iron rod is inserted in the solenoid along its axis. Obviously, self inductance of the solenoid will increase by some factor. [One can assume some resistance of of the solenoid...
23. ### Why is the induced current zero when a magnet is inside a stationary coil?

Basic question about Faraday's law? Hi guys, Ok I have a small problem with faraday's law. Taking the example of a north pole of a magnet coming close to a solenoid. My question is when the magnet is inside the coil and is stationary why is the induced current zero. Wouldn't the magnetic field...
24. ### Confused about Polarity of Induced EMF (Lenz Law)

Hello, I am currently working through Faraday's Law and I am confused when my two textbooks don't explain how they set the polarity of V_{emf}, particularly when they say "the sign convention for V_{emf} is arbitrary in that it depends on the assumed direction for dS". How is the polarity...
25. ### Are There Limitations to Lenz's Law in Real-World Applications?

What are the limitations of Lenz law? If there where none, you could just move a magnet through a coil and keep moving it away, thus creating the worlds most powerful magnet. This seems highly unlikely. When moving a magnet towards the coil, the external magnet field induces a current in the...