Induction. Magnetic fields. Motion. And a visual look at how Lenz’s Law are used in eddy current brakes.
1-Minute Marvels
High speed trains and roller coasters have very powerful brakes. These brakes often make use of Lenz’s law. Lenz’s Law states that when we have a magnetic field induced by another magnetic field, the former will oppose the latter. And if the latter is motion, the former creates a force that slows down and stops the motion (you can read all about these brakes in the 1-Minute Marvels “Roller coaster cooking science (in-depth)” and find out why they are also called eddy current brakes).
We can see roller coasters and bullet trains stopping but how does Lenz’s Law actually look like? To have a better and more tangible appreciation of Lenz’s Law, we found a neat video demonstration from MIT (its only drawback is that it has no audio!).
In this demonstration, the gentleman in a lab coat (?!) first drops an iron ball through a copper pipe. The time taken is about 0.02 seconds. Then he drops a same-sized magnetic ball through the same copper pipe. Guess how long it took?
It took 4 seconds! That’s 200x slower! How does it work? The magnet has a magnetic field. As it moves through the copper pipe, it induces a current in the copper pipe. The induced current has a magnetic field that opposes the magnetic field of the falling magnet.
This is Lenz’s Law in action. The opposing magnetic field creates a force that slows down the magnet. And this is what eddy current brakes use.
If you had watched the video to the end, you would have seen what the falling magnet would have looked like if viewed from the top. Here’s another video, also viewed from the top, but this time, it shows not only the effect of Lenz’s Law on a magnet, but also compares it to a falling coin, on which Lenz’s Law has no effect.
Dive deeper into Lenz’s Law and we see the scientific phenomena of eddy currents, magnetic fields, electromagnetic induction, Faraday’s law of induction, and the principles of alternating currents. They are used not only in brakes, but also in induction stoves – you can read all about them in the 1-Minute Marvels: “Saving goodbye to the old flame“.
And once you understand them, you can see the world with new “lenz” and design something neat to save the environment (which is what two designers did in “Saving the world one cup at a time“)!
Like this? Then brake and stop to like me to discover more. All you need is a minute a day to explore the world’s marvels through the phenomenon of food!
photos: in order – depositphotos/sepavone; Wavebreakmedia
