01 Oster Experiment
I. Background
What is the Oster experiment? It is actually very simple, just placing a compass under an electrified wire. Why is this experiment so important? Why do the results seem bizarre? Of course, now some people seem to be very normal experimental results.
II. The Oster Experiment
The story originated in the early seventeenth century when an English doctor determined that electrostatics and magnetism were completely different from each other. Time flies to 200 years later, an Italian named Alexander Voda invented the battery. The human name became interested to find the relationship between electricity and magnetism. A magnet has a south pole and a north pole, and a battery has a positive and negative pole. Other than that there are no other similarities.
▲ Figure 1.1.2 Magnet and Battery
Let us learn about a Danish philosopher and scientist, Hans Christian Oster, who was a great believer in the philosophical ideas of Immanuel Comte. Oster believed that according to Comte’s philosophy, all things in nature are intertwined. Therefore forces and physical nature should be interconnected. He tried to prove through empirical science that all laws of nature can be deduced from reason, and that nature itself is the result of reason.
Starting in 1806, Oster did his best to test whether magnetism had an effect on electricity, or conversely what electricity could do to magnetism. Fourteen years of this work yielded nothing. In 1820, Oster placed a compass under a wire and found that the magnetic needle was deflected when the current was turned on. Oster knew that the compass was a small magnetic needle on a stand, and a permanent magnet nearby could make the small needle rotate. If a general-purpose electric wire can move the magnetic needle, it means that the current in it also generates a magnetic field, not in the battery but in the vicinity of the wire.
▲ Figure 1.1.3 Hans-Christian Oster
Let us see the details of Oster’s experiment below. The battery used by Oster consisted of a pair of copper and zinc rods immersed in an acid solution, and when he placed the compass under a wire with current flowing through it he saw the magnetic needle move. But the strange thing is that the magnetic needle did not move in the direction of the wire, or the opposite direction, its direction around the wire to form a circle, which is why the results of this experiment seems so strange.
▲ Figure 1.1.4 Direction of the magnetic field around the electric current
The current flows in the direction of the wire, and the direction of the generated magnetic field surrounds the wire. At that time people did not know that other forces had this characteristic. For example, gravity always points to the center of the earth, magnetism and electricity produce forces of attraction or repulsion, and for dragging or pushing objects the force is also in the direction of the person applying the force or in the opposite direction, but the magnetic force acting on the compass seems to make the needle rotate around the electric current.
No need to be surprised that it took Oster 14 years to make this discovery, because he understood that the direction of the force on the magnetic needle had been wrong. Another strange thing about the experiment is that electrostatic charges do not produce a magnetic field, only moving charges do.
Third, the importance of the experiment
The experiment is strange, but why is it important? First, the relationship between the current and the magnetic field is fundamentally different from what we know about magnetism as well as electricity. Second, the phenomenon of a magnetic needle moving on the outside of an energized wire allows us to study the laws of electricity and magnetism more systematically, which will produce more new equations and theories.
▲ Figure 1.1.5 Magnetic field inside a coil
For example, just a few months after Oster published his experimental record, a German scientist made the first instrument capable of accurately measuring electric current by winding a wire around a compass multiple times to increase the force of the magnetic field acting on the needle. 1825 another German scientist, Georg Ohm, used this device to discover the relationship between electric current and the properties of energized materials, including the temperature of the material. This led him to the concept of resistance, and in honor of his contribution the unit of measurement of resistance was named after him. Many of the equations we use today were discovered during this period.
▲ Figure 1.1.6 Equations related to electric circuits
The third point, which is based on the relationship between electricity and magnetism, also led to a spurt in the invention of practical electrical devices. Before Oster batteries were used for research in only three areas: first, to produce small electric shocks; second, to separate chemical elements by electrolysis; and third, to light arc lamps using many batteries. In the decades following Oster’s discovery, the following devices were invented: amperemeters, motors, electromagnets, transformers, generators, and the first practical telegraph. In fact you can trace all the electrical devices now in use back to this single discovery. It was indeed a big event.
Fourth, the hardships of discovery
Then again, how did Oster himself see this discovery? Of course, he knew that this discovery was very important. In fact, he discovered this phenomenon a few months before he published his research, but the battery was weak at that time, and because this discovery was so important, he replaced it with a strong battery and redid the experiment.
Unfortunately many people reading this process think that Oster’s initial experimental results were discovered by accident. Did you know that Oster explored the relationship between electricity and magnetism for 14 years, but people always ignore the painstaking process and attribute his success to an accident?
Oster, like other scientists of his time, was puzzled by the circle formed by the magnetic force around an energized wire, which was illogical according to Newtonian mechanics. To solve this problem, he thought that the current in the wire did not flow in a straight line, but in a spiral trajectory in the wire, thus also dragging the magnetic field to form a spiral direction.
▲ Figure 1.1.7 The magnetic field around an electric current and the magnetic force
In England a man from the lower class, without formal education, named Michael Faraday decided to systematically study the theory of the Oster spiral current. He found that the current did not flow along a spiral, but in a straight line along a wire, but simply produced a prototypical magnetic field acting on a magnet. Later he established the theory that magnetic fields produce circular electrostatic fields. This revolutionized the study of the theory of electric and magnetic fields, resulting in the theory of electromagnetic fields.
V. Postscript
Why do people believe in the theory of this low-education chemistry lab assistant? This involves how Faraday confirmed his theory through experiments.
References
[1] The tamer of lightning: a history of electricity: https://zhuoqing.blog.csdn.net/arTIcle/details/128426612
[2] Oersteds Experiment: Why it is Important & Why it is so WEIRD: https://www.youtube.com/watch?v=2yawV5ekyN0&list=PLepnjl2hm9tF- CxhyRFZi3Pujkq_V4pKP&index=19
