How is the penetration of eddy currents affected in conductive materials?

The penetration of eddy currents into conductive materials is influenced by the material's conductivity and the applied frequency. When the frequency is increased or when conductivity is increased, the effect is that eddy currents tend to flow closer to the surface of the material, which results in shallower penetration. This is described by the skin effect, where the depth of penetration into the material decreases as either frequency or conductivity increases.

Conversely, when frequency or conductivity is decreased, the penetration of eddy currents increases. Lower frequencies allow the eddy currents to flow further into the material, as they are less affected by the skin effect. Similarly, if the conductivity decreases, eddy currents encounter less opposition, allowing them to penetrate deeper.

In summary, the correct choice emphasizes that lower frequency or conductivity enhances the depth of eddy current penetration, thereby directly correlating with the principles of electromagnetic induction and material properties.