Electric coils
When electric current flows, an electric field is generated. It is a principal of the electromagnetism that governs how our universe works. Engineers can harness this principle to create and explain fascinating phenomenon.
I started the session with two applications of this principle. One was a magnetic electric train that seemingly ran continuously in circles through a copper coil and a magnet that seems to fall slower inside of a copper pipe. The students investigated the demonstrations, made theories, tested hypothesis and ultimately cracked the secrets these two activities seemed to hold.
When electric current flows through a coil of wire, the electric field is able to compound for each curl of the coil. In out train, the electricity was provided by the battery/train. Electricity was able to flow from one battery terminal, through a magnet on that terminal in contact with the copper coils, through the copper coil, creating a magnetic field, through the rear magnet on the battery and finally back into the battery completing the circuit.
The induced magnetic field from the electric flow interacts with the magnets on each end of the battery, allowing it to be pushed along within the coil! For more details on this, see "How to build the simplest electric train" video.
How to build the simplest electric train – part 1
How to build the simplest electric train – part 1
The students found the magnets had to be correctly oriented for the train to work, and that it didn’t work in the solid copper tube, which confirmed our explanation.
Copper normally isn’t magnetic, which is why the slow-drop demonstration is so baffling, but by applying the same learned electromagnetic principles in reverse the students were able to puzzle out the trick. Above, when a current flows a magnetic field is created, but the reverse is also possible! A changing magnetic field can also induce current to flow! Current for example, in the copper pipe! The induced current then induces its own magnetic field that opposes the original one. So when a magnet was dropped down the copper pipe, the pipe responded to the moving magnetic field with an opposed field that slows the falling magnet. It’s eery, and amazing, and the way most of our electric power is generated. Electric generators, and in fact most electric motors all work on this principle of a magnet’s motion converting or inducing current flow.
The basics of how inductors work, a demo showing an inductor filtering out high frequency signals, a quick low pass LC filter, and a demo showing the magnetic field created around inductors.