www.nortonkit.com 18 अक्तूबर 2013
Direct links to other DC Electronics pages:
Fundamentals of Electricity: [Introduction to DC Circuits] [What is Electricity?] [Electrons] [Static Electricity] [The Basic Circuit] [Using Schematic Diagrams] [Ohm's Law]
Basic Electronic Components and Circuits. . .
Resistors: [Resistor Construction] [The Color Code] [Resistors in Series] [Resistors in Parallel] [The Voltage Divider] [Resistance Ratio Calculator] [Three-Terminal Resistor Configurations] [Delta<==>Wye Conversions] [The Wheatstone Bridge]
Capacitors: [Capacitor Construction] [Reading Capacitor Values] [Capacitors in Series] [Capacitors in Parallel]
Inductors and Transformers: [Inductor Construction] [Inductors in Series] [Inductors in Parallel] [Transformer Concepts]
Combining Different Components: [Resistors With Capacitors] [Resistors With Inductors] [Capacitors With Inductors] [Resistors, Capacitors, and Inductors]
Looking at Electrons

Consider the drawing to the right. Here we see a representation of a single atom — the smallest possible unit of any given element. At the center of the atom is the nucleus, which consists of two kinds of particles: protons and neutrons. The number of protons determines exactly what element we're dealing with, and the number of neutrons is similar to (but not necessarily the same as) the number of protons. We will not be concerned with the nucleus in these discussions, except to note that each proton has a unit positive charge, while each neutron has zero charge.

In constant motion around the nucleus we find a number of electrons, shown here as black dots. Each electron has a unit negative charge, precisely balancing the positive charge on one proton in the nucleus. As you might expect, in a normal atom with no external forces applied, the number of electrons orbiting the nucleus is equal to the number of protons in the nucleus. As a result, the entire atom is electrically neutral, or uncharged.

The electrons in any given atom do not just orbit the nucleus haphazardly; rather, they occupy specific energy levels, or "shells," around the nucleus. Electrons will always try to occupy the lowest energy level available to them, dropping into a closer orbit if they can. However, scientists have found that there is a limit to the number of electrons that can occupy any shell; electrons beyond that limit must take a higher-energy position in a wider orbit around the nucleus.

The first, or innermost shell is limited to two electrons. Once those two electrons are in place, this shell is filled and will force all other electrons to occupy positions further away from the nucleus. The second shell can hold a maximum of eight electrons, while the third can hold eighteen. Mathematically,

Number of electrons possible = 2N2,

where N is the shell number, counting out from the nucleus. This gives us maximum shell capacities of 2, 8, 18, 32, 50 and 72 electrons in the first six shells. That is enough to account for all natural elements, with room left over for those heavy elements that have so far been created in the laboratory and then some.

Of course, this discussion is very basic, and doesn't cover any of the fine details that have been gradually learned. Deeper discussions belong in the realms of chemistry and nuclear physics, and as such are beyond the scope of these pages.

The factor that becomes useful in dealing with electricity and electrical phenomena is that those elements that have only one or two electrons in their outermost shells don't hold on to these outermost electrons very strongly. Therefore it requires little external energy to pull these electrons away from their parent atoms and move them someplace else. These electrons make all electrical activities possible.

In metals such as copper and silver, these outer electrons are essentially free to move around anywhere within the body of the metal. In these metals, the outer electrons are so loosely held that the thermal energy inherent at room temperature is sufficient to free them from their parent atoms. We can cause these electrons to move from one place to another in a variety of different ways. We'll be exploring such methods and the uses to which such moving electrons can be put in these pages.