Science Buddies: "Ask an Expert"

My son is trying to improve his project. The previous judges suggested "more data needed, project not well tested".
Could you please suggest what further testing could be done before the next fair.
The experiment proves that energy from electrical induction can pass from a primary coil in the road to a secondary coil in an electric car motor.
Initially, the primary coil and secondary coils are 3 inch steel rods wrapped in magnetic wire.
Tests 1. amount of voltage needed in in primary coil (Variac) to run motor (voltage detected by multimeter)
2. ideal distance separating 2 coils (ruler)
3. best orientation of 2 coils (protractor)
Next, the primary coil was made 3 feet long and the secondary coil in car remained 3 inches
The longer primary coil was not able to pass enough energy to the car to run the motor.
Now, realizing more power is needed in the primary coil (road)
1. He tried wrapping the primary coil with 5 strands of wire (more voltage, less resistance) - bulky setup with minimal effect -should data still be generated?
2. He is preparing a track with multiple 3 inch coils each separately powered, hopefully the equal size ratio of coil will keep the motor running.
Aside from getting this model to work, what type of data should be collected, what more should be done.
He has a great understanding of electronics and magnetism, so further communications will be with him.
Thank you for sharing your time and expertise.
-Diane

Hello and welcome to the forums.

This sounds like an interesting experiment. Most magnetism experiments seem to suffer from a lack of an understanding of inductors and transformers, but you say your son understands these topics. We will need additional information to provide more help.

The energy transmitted from the road coil to the car coil will depend on a number of factors, but the most important are the number of turns on the rod, the amount of current in the coil, and the distance from the primary (the road coil) to the secondary (the car coil). Voltage is a secondary effect, and while it doesn't hurt to include that information in the report, it is not what you need to measure first.

He could design a number of experiments, but it is important to control all variables (except the one you're varying ) Since this is in the high school forum, I don't think that the focus of the experiment should be on transformer parameters (mentioned above). The judges will expect everyone knows the basic electro magnetic equations. Is this an engineering project? If so, he might explore what would be practical ways to do this. This will involve looking at different materials for the coils and rods, and investigating their cost effectiveness.

We look forward to hearing more about the specifics of this experiment. Thanks.
Keith

Hi Diane,

It's not very exotic, but once the car is running, you could measure the car's speed (or time to complete a lap). So there would be graphs varying an input variable vs. the car's speed (or time).

Keith wrote:

Voltage is a secondary effect, and while it doesn't hurt to include that information in the report, it is not what you need to measure first.

Excuse me but Voltage is easy to measure without distrupting the circuits and in constant frequency and impedence circuits is an excellent primary measurement from which power (a secondary measurement because it involves voltage and current and phase) can be easily be calculated.

Diane, I'm assuming that you are using 60Hz AC in your primary coil (road coil). What is your son using for a "core" for this coil. You indicate a "rod". What is the rod made out of? I'll assume it is a mild steel. You need to do some research/reading on magnetic lines of flux. If you have a 3 foot long rod, then the flux density inside the rod maybe great, but the lines of flux that go from one end to the other outside the rod are spread out way too much for good magnetic coupling to occur.

You should seriously consider figuring out how to make the track have multiple poles so that at one voltage polarity peak, they would line up something like N-S/S-N/N-S/.... and then flip to S-N/N-S/S-N/... at the opposite voltage peak. The car's coil core should be shorter but not by more than 50% than the individual core length of the track coils. Alternatively, you could try orienting the coils transverse to the direction of travel in which case you would want the cores (car and road) to be much closer to the same length.

Are you using a DC motor in the car with a full wave bridge rectifier, capacitor, and variable voltage regulator? If you are, then you maybe able to improve the coupling by increasing the frequency in the primary coil. If not, I would recommend trying them. That would give you a lot of freedom to experiment with in terms of coils and primary circuit changes without having to worry about matching AC motor characteristics.

There is a lot of physics involved in this project because you not only have all of the complications of mutual induction, you also have phase shifts caused by relative motion of the primary and secondary coils. Having an Oscilliscope available to help figure out what is going on would be ideal.