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Can anyone explain - what is the difference between static and varying electro-magnetic fields?

I know the definition for what is static electric field. It does not change with time (0Hz frequency.) But I don't know the exact meaning of that.

Also, can a Faraday cage stop only the static electric field? Can it shield both the static or varying magnetic fields? How?

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  • \$\begingroup\$ A static field's magnitude does not change over time.. it is constant. Is that what you don't understand? Or can you try to explain it in more detail? \$\endgroup\$
    – Jakob Halskov
    Commented Nov 18, 2019 at 11:19
  • \$\begingroup\$ The questioner also wants to know if/how a faraday cage (wire screen? or solid foil?) can shield against a changing magnetic field. \$\endgroup\$
    – analogsystemsrf
    Commented Nov 18, 2019 at 11:40
  • \$\begingroup\$ "It does not change with time [..]. But I don't know the exact meaning of that." I don't understand how you can not understand that. What's unclear? If something doesn't change it just stays the way it is. Concerning electric field: its magnitude and its direction doesn't change over time at any location. \$\endgroup\$
    – Curd
    Commented Nov 18, 2019 at 14:22
  • \$\begingroup\$ Hi Curd, I can understand that. But Actually what I don't understand is we are using Faraday cage to reduce the radiations from our circuits. The emission from the circuits are varying feilds at different frequencies. Many of them are saying the Faraday cage is for sheilding static fields. That's where my concern is. If that so, how the Faraday cage is used for sheilding the varying fields? \$\endgroup\$
    – M.Arun kumar
    Commented Nov 19, 2019 at 13:04
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    \$\begingroup\$ "Many of them are saying the Faraday cage is for sheilding static fields." they are mistaken. en.wikipedia.org/wiki/Faraday_cage \$\endgroup\$
    – Bruce Abbott
    Commented Nov 19, 2019 at 18:13

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[ edited the diagram, to show TWO INTERNAL METALLIC BAFFLES that prevent a direct line-of-sight. ]

here is my thought on the Efield thru a hole in a Faraday Cage.

Why can we trust this diagram? Because the flux lines are also modeled ---exactly, in shape and in intensity --- by the current flows in a finite element grid; in such a grid, there may be attenuation BUT the currents into and out of a grid_element will not be zero. Very small currents are NOT zero currents, hence the interior of a Faraday Cage, with a HOLE, is not ZERO current.

schematic

simulate this circuit – Schematic created using CircuitLab

What does this sketch tell us? Notice there are Efield flux lines everywhere into the cavity.

If the Efield changes, then the flux lines change and there will be currents (briefly) in the walls of the cavity. Should a circuit on a PCB also be within the cavity, then every point on your PCB will experience slight changes in currents (displacement currents).

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