# Electricity

## It's Elemental My Dear Watson

###### An atom is formed by protons, neutrons, and electrons:
• protons - particles have a positive charge , and along with neutrons, form the nucleus
• neutrons - particles have no charge (neutral), and along with protons, form the nucleus
• electrons - particles have a negative charge, and orbit the nucleus

To help you understand the electrical properties of elements/materials, locate "helium" on the periodic chart. It has an atomic number of 2, which means that it has 2 protons and 2 electrons. It has an atomic weight of 4. By subtracting the atomic number (2) from the atomic weight (4) you learn that helium also has 2 neutrons.

The Danish physicist, Niels Bohr, developed a simplified model to illustrate atoms. This illustration shows the model for a helium atom. Notice the scale of the parts. If the protons and neutrons of this atom were the size of a soccer ball, in the middle of a soccer field, the only thing smaller than the ball would be the electrons. They would be the size of cherries, and would be orbiting near the outer-most seats of the stadium. The only thing larger would be the space inside the atom, which would be the size of the soccer field.

One of the laws of nature, called Coulomb's Electric Force Law, states that opposite charges react to each other with a force that causes them to be attracted to each other. Like charges react to each other with a force that causes them to repel each other. A force is a pushing or pulling motion. In the case of opposite and like charges, the force increases as the charges move closer to each other.

Examine Bohr's model of the helium atom. If Coulomb's law is true, and if Bohr's model describes helium atoms as stable, then there must be other laws of nature at work. How can they both be true?

• Coulomb's Law - Opposite charges attract.
• Bohr's model - Protons are positive charges, and electrons are negative charges.

Question 1: Why don't the electrons fly in towards the protons?

• Coulomb's Law - Like charges repel.
• Bohr's model - Protons are positive charges. There is more than 1 proton in the nucleus.

Question 2: Why don't the protons fly away from each other?

The answers to these questions is that there are other laws of nature that must be considered.

Following are the answers to each of the above questions.

Answer 1: The electrons stay in orbit, even though they are attracted by the protons. They have just enough velocity to keep orbiting, just like the moon around the Earth, and to not let themselves be pulled into the nucleus.

Answer 2: The protons do not fly apart from each other because of a nuclear force that is associated with neutrons. The nuclear force is an incredibly strong force that acts as a kind of glue to hold the protons together.

The protons and neutrons are bound together by a very powerful force; however, the electrons are bound to their orbit around the nucleus by a weaker force. Electrons in certain atoms can be pulled free from the atom, and made to flow. This is electricity - a "free flow of electrons" or "current".

Atoms, or groups of atoms called molecules, can be referred to as materials. Materials are classified as belonging to one of three groups, depending on how easily electricity, or free electrons, flows through them.

Electrical Insulators - Electrical insulators, or insulators , are materials that allow electrons to flow through them with great difficulty, or not at all. Examples of electrical insulators include plastic, glass, air, dry wood, paper, rubber, and helium gas. These materials have very stable chemical structures, with orbiting electrons tightly bound within the atoms.

Electrical Conductors - Electrical conductors, or conductors, are materials that allow electrons to flow through them with great ease. They flow easily because the outermost electrons are bound very loosely to the nucleus, and are easily freed. At room temperature, these materials have a large number of free electrons that can provide conduction. The introduction of voltage causes the free electrons to move, causing a current to flow.

The periodic table categorizes some groups of atoms by listing them in the form of columns. The atoms in each column belong to particular chemical families. Although they may have different numbers of protons, neutrons, and electrons, their outermost electrons have similar orbits and behave similarly, when interacting with other atoms and molecules. The best conductors are metals, such as copper (Cu), silver (Ag), and gold (Au). All of these metals are located in one column of the periodic chart, and have electrons that are easily freed, making them excellent materials for carrying a current.

Other conductors include solder (a mixture of lead (Pb) and tin (Sn), and water with ions . An ion is an atom that has more electrons, or fewer electrons, than a neutral atom. The human body is made of approximately 70% water with ions, which means that it, too, is a conductor.

Electrical Semiconductors - Semiconductors are materials where the amount of electricity they conduct can be precisely controlled. These materials are listed together in one column of the periodic chart. Examples include carbon (C), germanium (Ge), and the alloy, gallium arsenide (GaAs). The most important semiconductor, the one that makes the best microscopic-sized electronic circuits, is silicon (Si).

Voltage - Voltage, sometimes referred to as electromotive force (EMF) , is an electrical force, or pressure, that occurs when electrons and protons are separated. The force that is created pushes toward the opposite charge and away from the like charge . This process occurs in a battery, where chemical action causes electrons to be freed from the battery's negative terminal, and to travel to the opposite, or positive, terminal, through an EXTERNAL circuit -- not through the battery itself. The separation of charges results in voltage . Voltage can also be created by friction (static electricity), by magnetism (electric generator), or by light (solar cell).

Voltage is represented by the letter "V", and sometimes by the letter "E", for electromotive force. The unit of measurement for voltage is volt (V), and is defined as the amount of work, per unit charge, needed to separate the charges.

Current - Electrical current, or current, is the flow of charges that is created when electrons move. In electrical circuits, current is caused by a flow of free electrons. When voltage (electrical pressure) is applied, and there is a path for the current, electrons move from the negative terminal (which repels them), along the path, to the positive terminal (which attracts them).

Current is represented by the letter "I". The unit of measurement for current is Ampere (Amp), and is defined as the number of charges per second that pass by a point along a path.

Resistance - Materials through which current flows, offer varying amounts of opposition, or resistance, to the movement of the electrons. Materials that offer very little, or no, resistance, are called conductors . Those that do not allow the current to flow, or severely restrict its flow, are called insulators . The amount of resistance depends on the chemical composition of the materials.

Resistance is represented by the letter "R". The unit of measurement for resistance is the ohm (O). The symbol comes from the Greek capital letter "O" - omega.

Alternating Current (AC) - This is one of the two ways in which current flows. Alternating current (AC) and voltages vary with time, by changing their polarity, or direction. AC flows in one direction, then reverses its direction, and repeats the process. AC voltage is positive at one terminal, and negative at the other, then it reverses its polarity, so that the positive terminal becomes negative, and the negative terminal becomes positive. This process repeats itself continuously.

Direct Current (DC) - This is the other one, of the two ways, in which current flows. Direct current (DC) always flows in the same direction, and DC voltages always have the same polarity. One terminal is always positive, and the other is always negative. They do not change or reverse.

Impedance - Impedance is the total opposition to current flow (due to AC and DC voltages). The term resistance is generally used when referring to DC voltages. Impedance is the general term, and is the measure of how the flow of electrons is resisted, or impeded.

Impedance is represented by the letter "Z". Its unit of measurement, like that for resistance, is the ohm (O).

Voltage, Current, Resistance Relationship
Currents only flow in closed loops called circuits. These circuits must be composed of conducting materials, and must have sources of voltage. Voltage causes current to flow, while resistance and impedance oppose it. Knowing these facts allows people to control a flow of current.

Ground - The term ground can be difficult concept to understand, completely, because people use the term for many different purposes.

• Ground can refer to the place on the earth that touches your house (probably via the buried water pipes), eventually making an indirect connection to your electric outlets. When you use an electric appliance that has a plug with three prongs, the third prong is the ground. It gives the electrons an extra conducting path to flow to the earth, rather than through your body.
• Ground can also mean the reference point, or the 0 volts level, when making electrical measurements. Voltage is created by the separation of charges, which means that voltage measurements must be made between two points. A multimeter (which measures voltage, current, and resistance) has two wires for that reason. The black wire is referred to as the ground, or reference ground. A negative terminal on a battery is also referred to as 0 volts, or reference ground.

Note: A multimeter is test equipment used for measuring voltage, current, resistance, and possibly other electrical quantities and displaying the value in numeric form.

Signal - refers to a desired electrical voltage, light pattern, or modulated electromagnetic wave. All of these can carry networking data.

One type of signal is analog An analog signal has the following characteristics:

• is wavy
• has a continuously varying voltage-versus-time graph
• is typical of things in nature
• has been widely used in telecommunications for over 100 years

The main graphic shows a pure sine wave . The two important characteristics of a sine wave are its amplitude ( A ) - its height and depth - and its period (T) - length of time to complete 1 cycle. You can calculate the frequency ( f ) - wiggleyness - of the wave with the formula f = 1/T.

Another type of signal is digital . A digital signal has the following characteristics:

• has discrete, or jumpy, voltage-versus-time graphs
• is typical of technology, rather than nature

The graphic shows a digital networking signal. Digital signals have a fixed amplitude but their pulsewidth and frequency can be changed. Digital signals from modern sources can be approximated by a square wave , which has seemingly instantaneous transitions from low to high voltage states, with no wiggles. While this is an approximation, it is a reasonable one, and will be used in all future diagrams.

PAM - Pulse Amplitude Modulation . Varies the amplitude or voltage of the electrical pulses in relation to the varying characteristics of the voice signal. PAM was the voice digitization technique used in some earlier PBXs.

PDM - Pulse Duration Modulation . Otherwise know as Pulse Width Modulation (PWM). Varies the duration of each electrical pulse in relation the variances in the analog signal.

PPM - Pulse Position Modulation. Varies the duration between pulses in relation to variances in the analog signal. By varying the spaces in between the discrete electrical pulses on the digital circuit, PPM focuses on the relative position of the pulses to one another as a means of representing the continuously varying analog signal.

PCM - Pulse Code Modulation . The most common voice digitization technique in use today. Eight bits or one byte are required to transmit the sampled amplitude of an analog signal. Since an 8-bit code allows 2 8 or 256 different possible values, each time the actual analog wave is sampled, it is assigned a value from 0 to 255 depending on its location or amplitude at the instant it is sampled.

CODEC - Coder/Decoder . The device(s) that samples an analog signal or transmission and transforms it into a stream of binary digits. In DS0 (1/24th of a T-1 and the basis for the DS, Digital Signal, standards which classifies the capacities of digital phone lines and trunks worldwide) the available bandwidth is 64 Kbps. In the case of the PCM codec which uses 8-bits per sample it is capable of 8,000 samples per second on the DS0 bandwidth. Which is to say that the PCM codec over DS0 is capable of transmitting 8KHz digital audio at 8 bit depth (256 different possible values) or 8,000 8-bit samples every second. Since POTS (Plain Old Telephone Service) uses a bandwidth of 4000 Hz or 4KHz the PCM (Pulse Code Modulation) codec using DS0 is fine for digitized voice with the sound quality of a telephone. However, the range of human hearing is between 20 Hz and 20 KHz or a 18 KHz range. Add to this the recommendation that you double your intended range when transferring analog to digital than we require at least 36 KHz to do hi-fidelity audio justice. You'll find that it is common to use 44 KHz at 16-bit depth sampling when converting hi-fidelity audio to digital format. Which means the required bandwidth to transmit such data is 704 Kbps for mono and 1.408 Mbps for stereo. Which is to say that without any compression, you would need a T-1 connection to send and receive hi-fi audio, no video mind you, over the PSTN (Public Switched Telephone Network).