# Help Needed. Electric Fields.

1. Sep 1, 2004

### hypnotik

Hey guys.
Im currently troubled with a physics theory that i cant explain, or prove.
The question:

Discuss whether it would be possible to design a similar train (Magnetic Levitated Train) by putting the electric field to use (and not using a magnetic field at all).

So i have to see if its possible to create a leviated train, with just the use of Electric Fields, and no magnetic fields. This is technically impossible because every electric field induces a magnetic field. Correct?

I need some more detailed insight on this question though.

hypnotik'

2. Sep 1, 2004

### daveed

well, wouldnt a huge electric field like that make current discharges in the surrounding?

trains are pretty heavy....

but dont count my opinion on it, im still learning physics

3. Sep 1, 2004

### Claude Bile

Maglev trains can acheive high speeds because they are not limited by friction forces. This is because the train does not sit on the rails, instead it is suspended above them (Hence Maglev: MAGnetic LEVitation).

While magnetic fields can be used to contain charged particles (and thus suspend the trains in midair), electric fields cannot. For a region of space with no free charges, Gauss' Law becomes;

$$\nabla \cdot \vec{E} = 0$$

Since, by definition,

$$\vec{E} = -\nabla V$$

Gauss' Law can therefore be written in terms of V

$$\nabla^2V = 0$$

This is Laplace's Equation. Laplace's equation implies, that for a region of space with no charge, there are no potential minima or maxima. Thus there is no region in space where the train can sit, it will be pushed one way or the other until it enters a region with a non-zero charge density.

Claude.

Last edited by a moderator: Sep 1, 2004
4. Sep 2, 2004

### hypnotik

Are you sure that is the correct understanding?

Could oyu provide more backing?..