Electro magnetic circuit setup

[johnluisfaz]

I am trying to set up a simple circuit described in a science project book. Suspending a thin insulated coiled wire over salt saturated water, the coil is supposed to contract due to a magnetic field created when the current is complete using a 6 volt DC battery. Various wire diameters and lengths have been tried to no avail. I can see a reaction in the water at the end of the coiled wire but it does not contract. For clarification, the thing coiled wire is attached to a solid copper wire conductor held by a styrafoam ball suspeded by inserting the ball with a pencil that is taped to a box for elevation. Any assistance would be appreciated.
John

[Craig_Bridge]

I don't understand your electrical connections from your description. Please start at the positive terminal of your 6v battery and describe what is attached to it and continue the description until you get to the negative terminal. From your description, I gather that you have a spring coil of insulated wire in it. It isn't clear but based on your observation of some chemical activity with salt water, I suspect that salt water is part of the circuit.

I'm also don't fully understand the properties of your coil: How many turns? What diameter are the turns? What is in the center of the coil? (Air, some coil form, plastic, ????). How long is the coil? How many layers? (a single layer of windings?) What pitch or spacing between turns? What is the coil length? What gauge wire? What material is the wire? (solid copper, stranded copper, aluminum, steel?) What insulating material if any is on the coil?

If your experiment is attempting to observe electro-magnetic forces between turns causes enough mechanical forces to exist between adjacent turns in a single layer pitched coil to cause the coil pitch to change and thus change its length, the amount of current flowing, the spring properties of the wire, and the electrical properties of the coil are going to be very important.

[johnluisfaz]

OK thanks for taking the time. The book made it look so simple and it did not give any specifics regarding the questions you asked as to the wire guage, length, coil length, number of turns or anything else. I'll try to answer as many of questions as possible. Starting at the positive terminal, I connected an insulated 12 guage copper strand about 10 inches long to the top of a solid copper wire 4 inches long taken from a ground wire of a standard 3 wire household wiring bundle. The book said to use a solid copper wire or nail. The solid copper wire is pushed through the styrafoam ball for support. The ball is pierced with the pencil. The pencil is taped to the top of a small box suspending the ball and solid copper wire about 12 inches from surface. Now to continue with the connection. The bottom end of the solid copper wire is connected to an insulated copper strand that extended is about 20 inches long. Using a pencil to form a coil of the 20 guage wire a single winding is made that results in a coil of about 5 inches in length. The bottom end of the coil is allowed to dip into the salt saturated water. The water is indeed suppose to be part of the current medium. I then complete the circuit by connecting a second 12 guage copper strand of wire from the negative terminal and dipping the other end into the water. Number of coil turns in about 12-15, diameter of coil is twice that of the pencil. Center of coil is air (I think this may be my problem, I may need to extend the solid copper wire down into the coil to allow a field to be created?) Pitch between wire coils is about 1/4 inch, naturally forming when wire is removed from pencil. All wire except the 4 inch solid copper is vinel/plastic coated. I agree that all properties mentioned are important however the science book used for reference did not give any specifics. I have done a little research to remind me of basic elctromagnetic properties and nearest I can tell is I have to much "leakage" due to air being the medium inside the coil. Hope this information is helpful enough for you to give me a little help. Thanks again.
John

[Craig_Bridge]

Thanks for the better circuit description.

For this "dancing coil" to work, the coil has to behave as a very weak mechanical coil spring and as an electromagnetic inductor capable of overcoming the gravitational forces and the spring forces.

By choosing PVC or similar insulated wire for your coil, you probably have increased both the weight and the mechanical spring constant beyond what the magnetic forces induced in your loosely wound 15 turn 1/2 inch diameter air core coil can overcome.

If I were trying this, I would use enameled magnet wire and would start with a smaller diameter wire, something between #24 and #30. Using magnet wire, I would try to get the coil pitch to be tighter, no more than two wire diameters between turns.

A no form air core is appropriate for this experiment. You definitely don't want any conductors inside the coil or near it as that will likely cause a reduction in the self inductance of the coil.

You want to minimize the surface tension between the coil and the salt water to minimize the force that is required to lift the coil. You also want to make sure that you have enough salt in your water to be a good conductor to maximize the amount of current flowing in the inductor to maximize the magnetic forces.

CAUTION: If you notice any green or yellow colored gas forming at the terminals in the salt water, you need to disconnect the battery immediately as this would be chlorine gas which is VERY toxic. This experiment should be conducted in a well ventilated area.