Principles of electricity/Electrons and Electric Fields
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Electrons and Electric Fields
Welcome to the lesson. If this is your first exposure to electrical theory, you need some foundational concepts in order to proceed through other electronics modules. The nuts and bolts of electricity are electrons, proton-packed atomic nuclei, atoms, molecules, void spaces, and the forces that extend across the voids between the solid particles. First, consider those particles.
Know subatomic nuclear physics?
Electrons have a negative charge. Call it negative 1 electron volt. Neutrons are neutral. Protons have a plus 1 electron volt charge. So, what is a charge? Charge is the potential to attract or repel another charged particle. Positively charged particles are mutually attracted to negatively charged particles. Positively charged particles repel positively charged particles. Negatively charged particles repel negatively charged particles. Unlike charges attract. Like charges repel.
It is a quirk of the universe that electrons and protons carry charges of identical magnitude. Use simple addition and subtraction to add or take away the charges of electrons or protons. There are other physical effects that bias this behavior but the description above will suffice in almost every circumstance you will encounter. We have to cover one immediately
The nuclear force is short ranged. Something about the order of the diameter of four or five protons is where it begins to drop off. However, it is quite strong enough over its short range to keep the proton-packed nucleus of an atom together. That is, until you get past Lead on the periodic table of the elements. The reason we have to brush on this topic is so we can move past the problem of positively charged particles sticking together in the nuclei of our atoms. Take it as given, until the nucleus gets pretty sizeable, it does not want to split.
Attraction and repulsion
Atoms are formed with a central, positively charged nucleus. This nucleus contains one or many protons and some neutrons. The protons each carry a charge that attracts nearby electrons. An atomic nucleus typically holds electrons in orbit by this positive charge. However, an atom is defined by its nucleus, not by its electrons.
So an atom has a cloud of electrons spinning at some distance from the nucleus. In a molecule or compound, the amount of attractive force in one atom may be different from its neighbor. An electron will migrate toward the more attractive atom. The one with the most apparent positive charge.
Electrons can change their orbit. With the application of energy, an electron can be induced to speed up, rise to a higher orbit, then stay there until induced to change orbit again. As the electron's orbit gets higher and higher, the strength positive charge of the nucleus acting on the orbiting electron is diminished. Taken to its conclusion, the electron can be forced to leave its atom.
In conductors, which include most metals, electrons are frequently shared between adjacent atoms. Should one electron be forced off its neighbor, it may in turn displace the neighbor's shared electron, which displaces the next and so on.
Long distance relationship
Force felt is related to charge by the inverse square of the distance. At a distance of 1 unit, electron A feels 1 unit of repulsion from electron B. At twice that distance, or 2 units, the repulsion would be the inverse of 2 squared or 1/2^2 or 1/4 the force at 1 unit of distance.
Electrons orbit atoms, are shared by atoms, and electrons can be forced away from atoms to fly off on their own. Happily, their behavior is predictable. Before an electron can accelerate to a higher orbit, it must be supplied with the force to speed it to the new orbit. In another galactic convenience, it has been demonstrated that electrons that move to a higher shell do so only in fixed units. Heard of quantum mechanics? Quantum physics? Well, a specific, exact, measurable quantum (quanta?) of energy is required to raise the electron exactly one orbital level. No more and no less will suffice. What happens when that orbit is allowed to decay and the electron loses energy? Can you guess? Put down your hand, brainiac. Each orbital unit of decay releases a quantum of energy precisely equal to the one that raised the electron in the first place. Where this becomes important is in things like light bulbs. Remember the loose treatment of electrons by nuclei in metals? Well, when the tungsten filament in a light bulb gets way, way hot, the electrons actually leave and bounce around inside the bulb! When they happen to fall back in toward the filament, they give off those quanta of energy in the form of light and heat.
Since we understand the forces involved between charged particles, we now have the mental tools to understand a bit about magnetism. Magnets posses mechanically and chemically fixed electron biases. That is, electrons would appear to be trapped toward one side of the atoms and molecules that make up fixed magnets. This fixing means that one end of the magnet has a relative surplus of negatively charged electrons. The converse holds true, where positively charged atomic nuclei are lain relatively bare. As this is at the molecular level, one can split a fixed magnet and the polarization remains for both fractions of the original magnet.
With every electron to the back of its attendant atom, the total charge across the magnet remains neutral. However the near surface is absolutely full of protons (for example) while the rear surface is absolutely full of protons. By our distance squared rule, we can easily see how the near positive charge outweighs the relatively distant negative charge.
Splitting a fixed magnet should produce diminishing magnet strength consistent with the decreasing inverse distance squared. [I have not seen this theory presented in any textbook so I must bear the responsibility if this is just plain wrong]
There is a way to create a magnetic field artificially. By coiling a conductor as you might coil thread on a spool, then applying an electric current, a magnetic field is induced. There is a left-hand rule for electromagnets. Look at the electromagnet. Put your left thumb in parallel with the core of the coil. If you can close your hand in the direction the electrons flow, then your thumb is pointing toward the North pole of the magnetic field. Otherwise, reverse your hand..
North and South
The north pole of a magnet attracts the south pole of another while like poles repel. Magnetic field forces electrons to rotate around magnetic field lines. There are units of measure for magnetic field strength. They are beyond the scope of this lesson.
I may have the polar electron attraction/repulsion backwards. Same with the left-hand rule. Experiment among yourselves. Document your results.
For extra credit, visit Earth's magnetic north and south poles. Report your observations.