Oersted’s Experiment: Why it is important and Why it is so Weird

What was Oersted’s experiment?  Well, it was incredibly simple: Oersted put a compass near a wire.  Wait, why is that important? And hey, why is that weird, sounds pretty normal to me.  Well, I’ll tell you in this video.  Ready?  Let’s go..

This story begins in 1600.  That was the year that an English doctor wrote a book on magnets and determined that static electricity was completely separate from magnetism.  Flash forward two hundred years, to 1800, when an Italian named Alessandro Volta invented the battery.  Suddenly, there was renewed interest in finding a connection between electricity and magnetism.  It seemed logical, magnets always have a North and a South and batteries always have a positive and negative.  Still, nothing! 

This brings us to Denmark and a philosopher and scientist named Hans Christian Oersted who was a big fan of the philosophy of Immanuel Kant.  To Oersted, Kant’s philosophy meant that everything in nature was intertwined, so the forces in Physics should also be connected.  He was determined to, “prove from empirical science how the laws of nature form a rational whole, and how nature itself is a revelation of reason.”  Beginning in 1806, Oersted tried everything he could think of to see if magnets could have an effect on electricity or visa versa.  For the next 14 years, a whole bunch of nothing.  Then, in the spring of 1820, Oersted put a compass underneath a wire and found that the compass needle turned when the current was running through the wire! 

Now Oersted knew that a compass is just a small magnet on a pivot so it can spin around.  That is why you can make a compass needle move by placing a magnet near it.  So, if the current in the wire moved the compass, that means that electrical current creates a magnetic force!  Oersted proved that electricity and magnetism was linked: not through the battery but in the current. 

Let’s go into a little more detail about what Oersted did.  Oersted used a battery that was composed of copper and zinc rods in an acid bath.  He then placed a compass under a wire in the closed circuit and voilà, the magnet in the compass moved.  Strangely, the magnet did not move to point with the wire, towards the wire or away from the wire.  No, the magnet moved to point in a circle around the wire! 

This is why the experiment is so strange: the current flows through the wire and the magnet points around the wire.  Think about it, there are no other forces that work like this.  Gravity pulls you towards the center of mass.  Magnets and static electricity either pull towards or push away.  Even directly pulling or pushing is either towards or away from the person pulling or pushing.  But compasses feel a force pushing them to point in a circle around the wire.  No wonder it took Oersted fourteen years to discover it, he (and others) were putting their magnets in the wrong orientation! 

The other thing that was, and is, very odd about this experiment is that it only works with moving charges, static charge has no effect on a magnet.  This is surreal but empirically true: static charges have no magnetic effects but moving charges do.

OK, why was this experiment important?  First, this experiment proved that electricity and magnetism are related, which is no small thing.  This is a fundamental change in our understanding of both electricity AND magnetism.  Statically, they are different things, moving they are two sides of the same coin. 

Second, the fact that external compass moves if there is current in a wire made it possible to study electricity and magnetism more systematically, which led to a profusion of new equations and theories.  In the same year that Oersted published his account, a German scientist wrapped a wire multiple times around a compass (to increase the force on the compass) and made the first calibrated machine to measure the strength of current.  In 1825 another German named Georg Ohm used this device to determine the relationship between current and the properties of the material that it runs through including it’s temperature.  He then created the idea of resistance, which is measured in Ohms in his honor.  In fact, many of the electrical equations we use today were born in this time period.

Third, the relationship between electricity and magnetism also started an avalanche of practical electrical devices.  Before Oersted, batteries were only used for three things, 1) to give small electrical shocks, 2) to electrically isolate chemicals, and 3) to create a bright light that required too many batteries to be practical.  Within twelve years of Oersted’s discovery, the following objects were invented: the ammeter, the motor, the electromagnet, the transistor, the generator, and even the first practical telegraph!  In fact, you can trace back all of our electrical devices to this single discovery!   It is a big deal.

So what did Oersted think of his discovery?  Well, he knew it was important.  In fact, He successfully did the experiment a month before he published his findings, but the battery was a little weak so he repeated it with a stronger battery, “considering the importance of the subject.”  Unfortunately, many people who read this thought that Oersted’s initial experiment was an accident.  So, instead of Oersted being lauded for fulfilling a 14-year quest, he is most often rumored to have done it by chance! 

Also, Oersted, like most scientists at the time, was perturbed by the fact that the current goes one direction and the magnetic force moves in a circle around it.  That seemed totally illogical to people used to Newton’s laws.  To “solve” his problem he decided that the electricity was really not moving straight down the wire.  Instead the electricity was spiraling down the wire and dragging the magnets in a spiral direction too.  In fact, he made it even more complicated because he believed that there were two types of current (a negative and a positive one) that were mutually spiraling around each other where each one was pushing it’s own pole, “negative electricity moves in a spiral line that propels the north pole, but does not act on the south pole.  [and] the effects on the south pole are explained in a similar manner.”

In England a lowly and uneducated chemical assistant with no math skills named Michael Faraday attempted to systematically and experimentally verify Oersted’s theory about the spiraling currents.  He came up with this strange theory that the current wasn’t spiraling, it was going straight down the wire, but it somehow emitted this circular force field that pushed on a magnet.  He also theorized that a magnet emitted a force field that pushed on the current, too.  This strange theory revolutionized our understanding of magnets and electricity and started Faraday on the path to creating magnetic and electric fields!  But why did anyone listed to Faraday?  Well, Faraday’s theories were backed by dramatic experiments.  How Michael Faraday made the first electric motor, and infuriated his mentor in the process, is next time on the secret history of electricity

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