# Current flow through conductor immersed in water

1. Oct 12, 2014

### BernieM

I have a small conductive, non-magnetic particle in which I will induce a fairly strong electromagnetic field into using a flow of current. I will then disconnect the power source that makes the particle electromagnetic. How long will it take the magnetic effect of the particle to diminish? Particle conductivity is around 5x10^7 sieverts. Particle diameter (assume round) is about .1mm

2. Oct 12, 2014

### sophiecentaur

My first reaction would be to relate the rate of change of induced field around the particle to treat the particle as a half wave dipole and think of its resonant frequency. You will induce a current in this dipole (how will you couple it to produce a "strong field"?). The tuned frequency of a 2mm dipole is around 75GHz. So the decay time would be less than the order of the period (1.5 e-11 s).

3. Oct 12, 2014

### BernieM

It will momentarily be a part of a complete circuit as a dead short. Think rail gun where the projectile is momentarily in contact with the rails as part of the armature.
The time domain you mention I believe is way too short to be of use to me.
I was going to break the contact with the circuit using a very strong magnetic field and was hoping that in the short time that it retained it's magnetic field that I could accelerate it to a useful velocity (which isn't very fast, >.5m/s and <5m/s)
With as short a time as you mention, I think the magnetic field would have to be nearly astronomically strong to get it to those velocities. But that's why I am asking the questions, because I don't know for sure.

Last edited: Oct 12, 2014
4. Oct 12, 2014

### Staff: Mentor

The surface spark produced when such current through the particle is abruptly broken may result in the particle being vapourised, or at least alloyed with the contact surface.

EDIT forget that, the title indicates immersion in water. Conductive water?

Last edited: Oct 12, 2014
5. Oct 12, 2014

### BernieM

Water will be on the order of micro to millisieverts conductivity. Think typical ground water or river water(is there such a thing as typical? ok so not a whole lot dissolved metals in the water but some like calcium and iron,) not salt water.

6. Oct 12, 2014

### Staff: Mentor

I think you'll have no hope of getting worthwhile current through particles immersed in a conductive medium. You'd like the medium to conduct current to your particles but not bypass around them? I can't see it happening.

7. Oct 13, 2014

### BernieM

Water is not a good conductor. In World War II when the Germans could no longer get transformer oil for their power line transformers from the USA, they used deionized water in them with excellent results. When the particle is in circuit the resistance is extremely low in the path through the particle, while the resistance through the water is extremely high. It should work like a pair of resistors in parallel, one having high resistance, the other low, and so Ohm's law says most of the current will take the low resistance path to ground.

8. Oct 13, 2014

### zoki85

Haha, really? I didn't know that

9. Oct 14, 2014

### sophiecentaur

Not only ancient transformers but, in these modern times, High Power Radio transmitters use deionised water to cool anodes, at many kV, which dissipate hundreds of kW. Water is a pretty good insulator. But these particles would need to be chemically isolated from the insulating water or any ions from their surface would rapidly contaminate the water and it would no longer insulate.

10. Oct 14, 2014

### zoki85

Do you have some link? Modern high power radio transmitters I know about are all realised on the basis of solid state power electronics.

11. Oct 14, 2014

### sophiecentaur

I feel this is a bit like the Crocodile Dundee line:" that's not a knife, THIS is a knife!"
When I say High Power, I mean 100kW+ and here's the first one I found. I don't know how high power the solid state transmitters go but this valve transmitter is current, afaik.
There are also UHF TV transmitters that use 80kW+ Klystrons. They also have a water cooled collector, I believe, which operates at high Volts. Klystrons are terrific value with both high power and high gain- all in one device.

12. Oct 14, 2014