Electromagnetic Suspense - A Reasoning Story About Electricity and Magnetism

Author: Shigehisa Fukuda
Publisher:
Publish Date: 2006-11-01
Features:
4.4 Revisiting Ohm's Law
The speed of free electrons in a circuit is very slow, yet why does the light bulb light up immediately when the switch is turned on? This was a problem we encountered in the chapter, and it can be explained very simply using the electric field theory. Similar to what happens between the plates of a capacitor, when current flows through a resistor, there is a potential gradient inside it, meaning an electric field exists. Free electrons move within the resistor under the influence of this electric field (in reality, since electrons carry a negative charge, their direction of movement is opposite to the direction of the electric field). The relationship between free electrons moving in a circuit and the electric field is like that of cars on a traffic-jammed road and traffic lights: when all intersections are red, the cars in long lines come to a complete stop; when the lights simultaneously turn green, all the cars start moving at once. When the circuit switch is open, it's like a red light; when the switch is closed, it's like all the lights turning green simultaneously. In the instant the switch is closed, the electric field rapidly propagates through all the wires and creates a potential gradient in the resistor. Under the force from the electric field (the lights turning green), free electrons (cars) tend to accelerate continuously, but they are obstructed by the positive ions inside the resistor (narrow roads causing traffic congestion), so the free electrons (cars) can only move forward slowly at a constant speed. In this case, the greater the potential difference, the stronger the electric field, and the current also increases proportionally—this is Ohm's Law. Therefore, Ohm's Law is based on a more fundamental law: "charged particles experience forces in an electric field." Although Ohm's Law has a very wide range of applications, it is not an independent fundamental law within the theoretical system of electromagnetism. Thus, another question naturally arises: "If the propagation of the electric field is almost instantaneous, what is its speed?" Unfortunately, we cannot provide an immediate answer to this question now, and the author leaves the solution to this problem for later chapters.
5. The Field That Is Difficult to Verify
5.1 The Ether Exists in Space
According to our traditional imagination, there should be no matter in a vacuum. However, the protagonists of the electromagnetic world are electric fields and magnetic fields. Electromagnetic theory states that a field is a property of space, and naturally, it exists in a vacuum as well. This idea is hard to grasp—even Faraday and Maxwell, who first proposed the scientific concept of electromagnetic fields, did not believe that fields could exist in a vacuum. We encountered the same problem when exploring the nature of light: light waves must have some medium to propagate in a vacuum, so scientists who advocated the field theory believed that there exists an unknown substance called the ether in space. What exactly is the ether? At that time, scientists proposed various models, such as some believing it to be extremely rarefied and invisible to the naked eye, while others thought it was a flow of microscopic particles that could not be observed with ordinary means. Readers may temporarily imagine the existence of the ether, but its reality remains...