Our teacher asked us this question during the lecture for Power Electromagnetics. We know that Electric Fields and Magnetic Fields are easily transformable into one another. And they are used greatly in various systems.

He asked us why is it that almost all the electric machines are still based on exchange of magnetic energy? Why isn't electric field used for power exchange and interaction through air gaps for a machine?

  • \$\begingroup\$ It's a really strange question. But I have a feeling it has something to do with the fact, that electrical field will require some medium (conductor) for transferring energy. \$\endgroup\$ – Eugene Sh. Jan 23 '15 at 19:51
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    \$\begingroup\$ It's been ages for me since I've looked into things like this, but my first hunch would be to investigate the formula's around \$\varepsilon _0\approx 9 \cdot 10 ^{ -12 }\ \text{F/m}\$ and \$\mu _0 \approx 1 \cdot 10 ^{-6}\ \text{H/m}\$. Notice the difference in -12 and -6. \$\endgroup\$ – jippie Jan 23 '15 at 20:19
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    \$\begingroup\$ Commonest example of electric fields into mechanical energy (in this case, air motion) is the electrostatic loudspeaker. Studying them will help you understand Jippie's point. \$\endgroup\$ – Brian Drummond Jan 23 '15 at 20:54
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    \$\begingroup\$ Possibly because by the time you have a high enough voltage to produce a strong enough electric field which exerts enough force to do much work, you've run into the trouble of your insulator (air) breaking down and sparks flying everywhere. \$\endgroup\$ – brhans Jan 23 '15 at 21:55
  • \$\begingroup\$ People are now doing capacitive power transfer at levels which are "useful" with the increasing to switch efficiently at the GHz level. That helps deal with the E6 difference in Jippe's equations. \$\endgroup\$ – Russell McMahon Jan 24 '15 at 0:22

There are electrostatic motors. They can be a better choice than magnetic motors for some situations.

For example, check out this electrostatic motor that can be using in places with very strong magnetic fields like near MRI machines...


Electrostatic motors can also very efficiently directly use high voltage at very low current. The one described here can run forever off the voltage differential between two wires separated by a few dozen feet of height...


Here is a practical book with lots of electrostatic motor information, including many designs can build yourself...



Until the Gramme Machine, electrical machines were milliwatt-scale classroom demos and lab curiosities. Gramme's breakthrough idea was industrial scale, and was the basis for Edison's DC "bipolar" machines which took over the world in pre-Westinghouse days.

E-field devices, or Static Electric motors & generators, remain non-industrial because the max field is set by gas breakdown, and gives low torque at that limit. B-field machines have enormous torque at their core-sat limit. How big is a 1/4 horse electrostatic motor? How heavy? How expensive?

Think way outa box! Perhaps things will change in LEO or "Belter" industry, where megavolt circuitry in hard vac environment is cheap and common, and where cooling of coils and cores is near impossible. Fab up some capacitive micro-layer "muscles" for a thousand-HP linear motor which requires cleanroom conditions and vacuum as insulation.


You can transform an electric current into a magnetic field, which can exert forces. If you want a strong field, just make multiple windings. If you want a strong electric field you need a magnetic current. You can't make a conductor with flowing magnetic charges (since there are no magnetic charges). You can make a magnetic conductor with flowing magnetic displacement currents, but the separation between a magnetic field conductor and insulator is much worse than between an electric current conductor and insulator.

So it is more efficient to transport energy as electric current in metal wires where it can be very well contained, then apply it with a magnetic field. You could also apply it with an electric field, but you would need very high voltages. It's easier to make multiple windings.

I hope that made sense, I am glossing over a lot of technical terms to illustrate the symmetry between the systems.


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