# Metal ring repelled from AC coaxial coil

• nvalentour
In summary: This is known as Lenz's Law. So, in summary, the ring is repelled due to the induced emf in the ring, which is created by the changing magnetic flux in the solenoid, according to Faraday's Law of Induction and Lenz's Law.
nvalentour
I thought people helped on this forum?

If anything is unclear just ask, I'm checking for posts every minute. Come on people I have to get this done by 5 pm. I've gotten a little further. I believe it has something to do with mutual inductance.

A metal ring (no current) is brought close to a solonoid (coil with n turns), the solonoid has an alternating current running through it; explain using equations why the ring is repelled. (the ring is directly above the axis of the solonoid).

I think the di/dt of the coil induces an emf in the ring that follows Lenz's Induction Law and in turn creates a magnetic field with polarities facing each other, so they repel. I need this in equation form though. (Is my reasoning even correct?)... Please help.

Last edited:
The equation representing the phenomena is Faraday's Law of Induction:$$\mathcal{E} = - N \frac{d\Phi}{dt}$$where $\mathcal{E}$ is the induced emf, $N$ is the number of turns of the coil, and $\Phi$ is the magnetic flux. As the current in the coil changes, the rate of change of the magnetic flux also changes, and this induces an emf in the ring which opposes the change in flux and thus creates a repulsive force between the two objects.

Hello,

First of all, I want to assure you that people on this forum are always willing to help and provide assistance. It is possible that some may not have seen your post yet, or may not have the expertise to answer your question. I encourage you to be patient and give others a chance to respond.

Now, let's address your question. You are on the right track with your reasoning. The phenomenon you are describing is known as mutual inductance, which occurs when a changing magnetic field in one coil induces an emf in a nearby coil. This is described by Faraday's Law of Induction, which states that the induced emf is equal to the negative rate of change of magnetic flux through the coil.

In this case, the alternating current in the solenoid creates a changing magnetic field, which in turn induces an emf in the metal ring. This emf creates a current in the ring, which in turn creates its own magnetic field. According to Lenz's Law, this induced magnetic field will oppose the changing magnetic field that created it. Since the changing magnetic field in the solenoid is above the ring, the induced magnetic field in the ring will be in the opposite direction, resulting in repulsion between the two.

This can be expressed mathematically using the following equation:

emf = -N * ΔΦ/Δt

Where emf is the induced emf, N is the number of turns in the solenoid, and ΔΦ/Δt is the rate of change of magnetic flux through the solenoid.

I hope this helps to clarify your understanding. If you have any further questions, please don't hesitate to ask. Good luck with your project!

## What is a metal ring repelled from AC coaxial coil?

A metal ring repelled from AC coaxial coil is a demonstration of electromagnetic induction. It involves placing a metal ring, such as an aluminum or copper ring, above a coaxial coil that is connected to an AC power source. When the coil is energized, it produces a changing magnetic field which induces a current in the metal ring. This current creates its own magnetic field, causing the ring to be repelled from the coil.

## How does a metal ring repelled from AC coaxial coil work?

The metal ring repelled from AC coaxial coil works based on the principles of electromagnetic induction. When the coil is connected to an AC power source, it produces a changing magnetic field. This changing magnetic field induces a current in the metal ring, which in turn creates its own magnetic field. The interaction between the two magnetic fields causes the ring to be repelled from the coil.

## What factors affect the strength of the repulsion in a metal ring repelled from AC coaxial coil?

The strength of the repulsion in a metal ring repelled from AC coaxial coil can be affected by several factors. These include the strength of the AC power source, the number of turns in the coil, the diameter and material of the ring, and the distance between the ring and the coil. Generally, a stronger power source, more turns in the coil, and a larger and more conductive ring will result in a stronger repulsion.

## What are some real-world applications of a metal ring repelled from AC coaxial coil?

A metal ring repelled from AC coaxial coil has several real-world applications. One example is in electromagnetic levitation, where the repulsion between the ring and the coil is used to levitate objects. It can also be used in electrical transformers, where the changing magnetic field in the coil induces a current in the metal core, which is used to transfer energy. Additionally, this demonstration can be used to teach principles of electromagnetism in physics and engineering classes.

## Are there any safety concerns when conducting a metal ring repelled from AC coaxial coil experiment?

When conducting a metal ring repelled from AC coaxial coil experiment, it is important to take necessary safety precautions. The AC power source used should be low voltage and current to avoid electric shocks. It is also important to keep the coil and power source away from water and other conductive materials. Additionally, the experiment should be conducted under adult supervision, and proper protective gear, such as safety goggles, should be worn.

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