# An experiment with a charged electrolyte and magnet

1. Jan 20, 2012

### cosmicomic

Hi, I am a high school student and I'm planning on entering a regional science fair with an experiment involving electrolytes, magnets, and electric currents. However, I don't understand electromagnetism well enough to fully understand everything that would be going on in the experiment, and as a result, I can't really predict results or make a hypothesis. In fact, I don't know what I would be measuring besides "what would happen". I've spoken to both the physics teachers at my school and they weren't 100% sure what would happen, either, so I thought I'd ask here.

Suppose you had a container with an ionic solution in it, and it was hooked up to a battery so that it had a current flowing through it. What would happen if you dropped a magnet into the electrolyte?

I've done some research on magnetic fields, and I know that a magnet has a magnetic field with north pole and a south pole, and a wire with a current running through it also has a magnetic field. In the context of the experiment, how would these fields interact? I was thinking that the electrolyte might physically move, since the magnetic field would become distorted and probably have some influence on the ions in the solution.

Also, I believe the magnet falling through the water would make a moving magnetic field, and that would produce a current in the electrolyte (induction). However, the electrolyte would already have a current flowing through it from the battery. So there would be a current from the magnet and the current from the battery. How would those currents affect each other?

Thanks!
cosmicomic

2. Jan 20, 2012

### Simon Bridge

The currents add together - more accurately, the forces producing the currents add together.

Note: "just seeing what happens" is a valid experiment: you are exploring.
However, if you do this, you want to refine your subsequent investigation to isolate the various phenominon you observe.

Perhaps you should construct something that would allow you to control the movement of the magnet instead of just dropping it?

Or would you like to compare the time it takes the magnet to hit the bottom with the electric field compared to without (and with or without the electrolyte too)?

Maybe you want to see what the effect on the current is when the magnet is present and doing different things?

See, once you work out what variables you want to control, an experiment develops. Right now, you are too wide open.

3. Jan 22, 2012

### cosmicomic

I have now devised a more specific experiment based on a simple magnetohydrodynamic motor that I found online.

There will be a vat of electrolyte fluid that is hooked up to a battery so that a current is running through it horizontally. In the middle of the vat, there will be a plastic tube that is tall enough to stick above the surface of the water (so there's no water in the tube). Then, a neodymium magnet will be dropped down the tube. The magnetic field lines of the magnet will be perpendicular to the direction of the current. This will produce a Lorentz force that will be exerted on the water.

Plastic tubes of varying lengths will be used to change the speed of the magnet (longer tubes will allow for a longer time for acceleration due to gravity), and each time, I will measure the magnitude of the Lorentz force. The speed of the magnet won't be constant, however, since it will still be accelerating as it falls, so I am rather concerned about that. I can't think of any other way to change the speed of the magnet, though.

I am not sure how I will measure the Lorentz force. I'm thinking of placing a weigh boat on the surface of the water, and measuring how far it is pushed (by the Lorentz force). However, I doubt this is a very reliable or accurate way to gauge the magnitude of the force.

My greatest concern is that I have no idea if the speed of the magnet will have any effect on the Lorentz force produced. This is mostly due to the fact that I don't know why magnetic field lines perpendicular to a current will produce a force. The link I posted to the magnetohydrodynamic motor just says that it will.

Are there any flaws in this experiment (besides the ones I've already pointed out)? I have a hunch that there are a lot.