- #1

KDPhysics

- 74

- 23

- Homework Statement
- How does placing a conductor in the path of a magnetic field of a circular coil shield anything behind the plate?

- Relevant Equations
- Lenz's Law

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 currents popping up.

If I've understood everything correctly, when you place a conductor near a changing magnetic field (such as that of a circular coil), nature abhors any change in magnetic flux. Consequently, a current will be induced, called Eddy current, in the conductor, such that the induced magnetic field opposes the change in magnetic flux.

For example, I have the following set up (a circular coil attached to an AC supply and a conductor beneath it):

Now consider an arbitrary instant in which the coil's magnetic field is decreasing. Then, by Lenz's law an Eddy Current will be induced in the conductor trying to "undo" this decrease in magnetic flux. Consequently, the current will be such that the induced magnetic field points in the same direction as the external magnetic field.

But then there still is residual magnetic field behind the conductor due to both the decreasing external field and the induced field. So, shielding has not occurred?

After searching online, I repeatedly saw Eddy currents popping up.

If I've understood everything correctly, when you place a conductor near a changing magnetic field (such as that of a circular coil), nature abhors any change in magnetic flux. Consequently, a current will be induced, called Eddy current, in the conductor, such that the induced magnetic field opposes the change in magnetic flux.

For example, I have the following set up (a circular coil attached to an AC supply and a conductor beneath it):

Now consider an arbitrary instant in which the coil's magnetic field is decreasing. Then, by Lenz's law an Eddy Current will be induced in the conductor trying to "undo" this decrease in magnetic flux. Consequently, the current will be such that the induced magnetic field points in the same direction as the external magnetic field.

But then there still is residual magnetic field behind the conductor due to both the decreasing external field and the induced field. So, shielding has not occurred?