Electrostatic magnetic-field interaction

1. Nov 28, 2009

ace333

simple eg: negatively charged van de graaff generator top and a magnet. Put magnet near top. Would the magnetic field push the electrons of the charged surface to the sides and deeper into the metallic top?

2. Nov 28, 2009

ideasrule

A charged van de graaff generator is very nearly in equilibrium: it has very little current. Why would the magnet push the electrons in any way?

3. Nov 28, 2009

ace333

I'm referring to the localised area within a few millimetres from the magnet.

4. Nov 28, 2009

Bob S

Magnets have no effect on static charges, but slowly moving electrons curl up in a magnetic field. In a crossed electrostatic magnetic electric field, the electrons move in a cycloidic manner.
Bob S

5. Nov 29, 2009

ace333

Why is there no effect on static charges since the electrons are the same
free electrons as in a conductor and on those there is of curse such a
strong effect induced on the same free electrons by a magnetic field. What is the difference since the conductors free electrons are just as static as the electrostatic charge and it is only their abundance that is different. So why can’t they be moved by a magnetic field?

6. Nov 29, 2009

Bob S

The only force on a charge by a static magnetic field is when the charge is moving. It is given by the Loeentz force F:

F = q(E + v x B), where the 2nd term is the vector cross product.

The magnet can prevent slow electrons from moving toward (and "sticking to" for dielectric surfaces) surfaces near the magnet poles.
Bob S

7. Nov 29, 2009

ace333

"The only force on a charge by a static magnetic field is when the charge is moving."

So since movement is relative than as a magnet is being moved towards (or away) from the metallic negatively charged van de graaff top than the electrostaticly accumulated electrons could be effected, no?

8. Nov 30, 2009

Bob S

Good questions. When a magnet is moved toward or away from a metallic surface, eddy currents are induced in the metallic surface that slow down and retard the dB/dt (changes) in the magnetic field perpendicular to the metallic surface. However, changes in magnetic fields (dB/dt) parallel to the metallic surfaces (if non-magnetic) are only slightly affected. A rapid change in magnetic fields (dB/dt) can induce voltages (Faraday's Law) that will affect static electric charges. But the electric charges on insulators are bound to the insulator by an electrostatic potential called a work function that requires large local electric fields to remove. So even a large dB/dt is not likely to pull charges away from insulators. "Electrostatic" charges on metallic surfaces are image charges due to opposite sign charges either in space (space charge, including ion or electron beams) or on insulating surfaces elsewhere. These charges are unlikely to move.
Bob S

Last edited: Nov 30, 2009
9. Nov 30, 2009

ace333

THANK YOU> SO Is there a way to mix extra electrons (a non permanent net gain during exposure time) deep into a conductor momentarily without biologically damaging methods? Like electrostatic charging and discharging i.e. moving charges, coupled with rapid pulsed electromagnetic fields? Would the moving charges (high voltage electrostatic) be affected by the changing magnetic fields enough to move off the surface deeper into the conductor momentarily?