I like analyze the physics of science fiction, so I’m going to argue that Merrie Melodies’ cartoon “Compressed Hare” takes place in the distant future where animals rule the world. I mean, Bugs Bunny and Wile E. Coyote walk on two legs, talk, and build stuff. How could that not be science fiction?
Let me set the scene and I don’t think we have to worry about spoiler alerts since this episode is 60 years old. The basic idea is, of course, that Wile E. Coyote decided he should eat the rabbit. After a few unsuccessful attempts to catch Bugs, he comes up with a new plan. First, he’s going to drop a carrot-shaped piece of iron into Bugs’ rabbit hole. Once the carrot is consumed (and I have no idea how that would turn out), Wile E. Coyote will light a giant electromagnet and pull the rabbit straight towards him. It’s such a simple and awesome plan, it just has to work, right?
But wait! Here’s the part I really like: As Wile E. Coyote assembles his contraption, we see that it comes in a huge crate labeled “A DIY 10,000,000,000 Volt Electric Magnet Kit” .
Ultimately, you can probably guess what’s going on: the bugs aren’t actually eating the iron carrot, so once the coyote turns on the magnet, it just zooms in on it and into its cave. And of course, a bunch of other things are drawn to it as well, including a lamppost, a bulldozer, a giant cruise ship, and a rocket.
OK, let’s break down the physics of this massive electromagnet and see if it would have worked if Bugs had fallen in love with him.
What is an electromagnet?
There are basically two ways to create a constant magnetic field. The first is with a permanent magnet, like those things that stick to your refrigerator door. These are made of some type of ferromagnetic material like iron, nickel, alnico or neodymium. A ferromagnetic material essentially contains regions that act like individual magnets, each with a north pole and a south pole. If all of these magnetic domains are aligned, the material will act like a magnet. (There are some very complicated things happening at the atomic level, but let’s not worry about that just yet.)
However, in this case, Wile E. Coyote has an electromagnet, which creates a magnetic field with an electric current. (Note: We measure electric current in amps, not to be confused with voltage, which is measured in volts.) All electric currents produce magnetic fields. Normally, to make an electromagnet, you have to take a wire and wrap it around some ferromagnetic material, like iron, and turn on the current. The strength of its magnetic field depends on the electric current and the number of loops the wire makes around the core. It is possible to make an electromagnet without an iron core, but it will not be so strong.
When the electric current creates a magnetic field, this field then interacts with the magnetic domains of the piece of iron. Now this iron Also acts like a magnet – the result is that the electromagnet and the induced magnet attract each other.
What about 10 billion volts?
I don’t know how the script for this episode came about, but in my mind, a group of writers were working together. Maybe someone came up with the idea of an electromagnet and an iron core and everyone agreed to put that in there. Surely someone raised their hand and said, “You know, we can’t just make an electromagnet. He must be exaggeratedly big. Another writer must have replied, “Let’s put a number here. What about 1 million volts? Someone else jumped in, “Sure, 1 million volts is cool—but what about 10 billion volts? “
What does 10 billion volts mean for an electromagnet? Remember that the most important thing about an electromagnet is electric current (in amps), not voltage (in volts). To make a connection between voltage and current, we need to know the resistance. Resistance is a property that tells you how difficult it is to move electrical charges through a wire, and it’s measured in ohms. If we know the resistance of the wire of the electromagnet, then we can use Ohm’s law to find the current. As an equation, it looks like this: