Induction and Electromagnetism – Veritasium

In the last Veritasium video, we explained that wireless inductive charging worked almost like an electromagnet in reverse. In your standard elementary school electromagnet, you run a current in a coil of wire wrapped around a nail to induce a magnetic field (check out the discussion of the first video if you don’t know what I’m talking about). Induction works the opposite way where a quickly moving or changing magnetic field is able to produce current. You can use this effect to essentially beam power over air gaps as demonstrated in the first video.

Now lets take this concept one step further. We’ve already established that there is a relationship between electric current and magnetism that can be manipulated to work in both directions. Can we use the principles of induction to produce a magnetic force in a non-ferrous conductor like copper or aluminum? What do you think? Here’s a hint: think about the “levitating¬†barbecue” from the first video. Intuition will tell you that copper and aluminum are not magnetic. That’s why the simple demonstration in these new videos will surprise you:


And here’s a further explanation from a professor at Nottingham University:


So it is possible to produce a magnetic attraction in copper and aluminum. The key to the process is that the conductor has to be a circular shape and the magnet has to pass through the center of it at a decent speed. Here’s an easy way to think about it: picture the copper tube as the coil of wire around the nail in that same elementary school electromagnet that you built. In the discussion for the first Veritasium video, we talked about how the current flowing in a circle through the coil causes a magnetic field in the nail because of the right-hand rule. The current is supplied to the coil of wire by the battery. With the magnet in the pipe demonstration, we obviously don’t have a battery. So how does the copper pipe produce an electromagnetic force? The answer is that we are adding energy to the system through gravity. There are two separate processes happening:

1. The magnet falls through the pipe. We input the energy to the system by lifting the magnet up to the top of the pipe. As gravity pulls it to the bottom of the pipe, it’s picking up speed. As we’ve already discussed, the moving magnetic field produces a current in the pipe.

2. The current in the pipe flows in a circle like the coil of wire on the nail and battery electromagnet. This produces an electromagnetic field in the opposite polarity of the magnet falling through the pipe. That’s why it resists the magnet’s motion and it takes longer for the magnet to fall than the chunk of aluminum.

You could say that dropping the magnet through the copper pipe is making an electromagnet powered by induction. It’s kind of neat to see both processes demonstrated in one simple experiment. If you can wrap your mind around this then you pretty much understand why electric motors are also generators based on the magnetic phasing or rotation direction.

Sources: Veritasium and Sixty Symbols on YouTube

Wireless Inductive Charging Explained – Veritasium

Hopefully you have built one of these simple electromagnets somewhere along your journey to become an educated human being. If you understand the basic principle of how an electromagnet works, then you can understand how wireless inductive charging works. In an electromagnet, the flow of electrons (current) causes a magnetic field. The magnetic field forms at a right angle to the direction of the current (the right hand rule). That means as the current flows in a circle around the nail (the fingers of your right hand wrap around the nail), the magnetic field forms along the nail (your right thumb points in the direction of the magnetic field) putting the poles on either end of the nail. If you’ve built one of these basic nail magnets, then you intuitively understand this already.

Here’s the really cool part. This relationship between current and magnetism works in reverse. A fluctuating magnetic field will also create a current in an otherwise dormant wire. Sustain the situation and you will eventually produce enough current to charge a battery. This is usually done with two coils of wire similar to the ones you wrapped around that nail to make an electromagnet. One of the coils is hooked to a power source and the other coil is hooked to whatever it is you’re trying to charge. The coil connected to the power source becomes an electromagnet that is switched on and off at very high frequency. This transforms the electrical energy into a usable form of magnetic energy. When the second coil is in range of the fluctuating magnetic field of the first coil, it transforms the magnetic energy back into electrical energy like an inverse electromagnet. Rapidly turning the electromagnet on and off allows you to broadcast energy as a magnetic field that can travel through the air without a physical wire connection. Check out this video from Veritasium to see how these principles were first discovered and a rad magically illuminated floating grill that would be perfect in a science nerd man cave.


Source: Veritasium on YouTube via IO9