Electronics Information Review

How is electricty produced?

The electricity used in the United States is predominately produced from three resources: fossil  fuels, such as oil, natural gas, and coal; nuclear materials, primarily uranium; and hydropower  from water. 

Almost 80 percent of the electrical power used in the United States is produced from the burning of fossil  fuels. Fossil fuels are burned to produce heat. The heat is used to produce steam that turns a turbine. The turbine  transforms rotational mechanical energy into electric energy which in turn is fed into a power grid. 

Nuclear power plants produce about 7 percent of the electricity we consume. A nuclear power plant uses  a nuclear reaction (fission) to produce heat that generates steam. The process described above is then used to convert  steam into electricity. 

About 15 percent of the electricity we use is from hydropower. The kinetic energy of falling water is used  to turn turbines that produce the electrical power. 

Kinetic Energy: the energy produced by a  body in motion. 

Basic Electrical Theory 
Understanding electricity and electronics is not  dependent on understanding the complex structure of  the atom—understanding the basics is sufficient. All  materials on Earth are made up of atoms. An atom is  made up in part of electrons and protons. These two  subatomic particles each have an electric charge, or  electric polarity. The charge of an electron has a negative  polarity while the charge of a proton has a positive  polarity. Electricity is essentially the management of  positive and negative electric charges. 

Charge 
Most everyone has experienced the buildup of electric  charge when shuffling across a carpet. Your body develops  a static charge. It is static because the charge is not  moving. When you touch a light switch, the static  charge moves, creating a current. You have produced  and used electricity. 
The symbol for electric charge is q or Q. Charge  is measured in coulombs, C. A coulomb of electrons  has a negative charge and a coulomb of protons has a  positive charge. A coulomb is defined as 6.25  1018  electrons or protons:  the charge of 6.25  1018 electrons = Q = 1C 

Voltage 
An electric charge has the potential to do work by forcing  another charge to move. Opposite charges attract  each other and like charges repel each other, just like  magnets. Thus, a positive and a negative charge would  attract each other, while two negative charges would  repel each other. The potential of an electric charge to  do work is the voltage or the potential difference. A  battery produces a voltage. This voltage can be thought  of as the force that moves electrons from one terminal  to the other. This force is called the electromotive force  (emf). The accepted symbol for voltage is V. The  schematic symbol for a DC voltage is:  Voltage: the potential of an electric charge to  do work. 

Current 
All batteries have two terminals, a positive and a negative  one. On a flashlight battery, for example, one end  (usually marked with a + sign) is the positive terminal,  and the other end (usually marked with a  sign) is the  negative terminal. 
When a battery is connected to a load with wires,  the potential difference, or voltage, between the two terminals  (the two opposite charges) forces a third charge  to move. The charge in motion is called an electric  current. Current is produced when a potential difference  moves an electric charge. Picture a battery connected  with wires to a light bulb: 

The battery produces a voltage, which forces the free  electrons in the wire to move. The mobile free electrons  moving in the wire are the current. The current is  always a continuous flow of electrons, and at every  point in the circuit, the current is the same. 

Load: the resistance in an electric circuit. 
Electric current is measured in amperes. An ampere is a unit of measure of the rate of electron flow or current in an electrical conductor. One ampere of current represents one coulomb of electrical charge (6.24 x 10^18 charge carriers) moving past a specific point in one second.

This is the same as one  coulomb of charge moving past any given point in one  second. The symbol for current is I or i. Mathematically,  current is expressed as: 

The current can be found from Ohm's Law, V = IR. The V is the battery voltage, so if R can be determined then the current can be calculated. 

Alternating Current (AC) and Direct Current (DC) 
A battery is an example of a direct voltage source. The  terminals of the battery always maintain the same  polarity, so the current flow from one terminal to the  other is always in the same direction. On the other  hand, an alternating voltage source periodically reverses  its polarity. The current resulting from an alternating  voltage also periodically changes its direction of flow. 
The electricity generated in a power plant is by  nature an alternating voltage. The magnetic fields  developed in a rotating turbine always produce an  alternating voltage. The voltage we most often use in  our homes is 110 volt 60 Hz. The 60 Hz, or Hertz,  refers to the frequency that an alternating voltage  changes polarity. In this case the polarity changes  from positive to negative and back to positive 60  times a second. 
One advantage of producing an alternating  voltage is that it is more easily changed to a different  value than a direct voltage can be changed. This is  very important because power plants produce thousands  of volts, while we can safely use just 110 or 220  volts in our homes.Most of our appliances then convert  the 110 or 220 volts to even a smaller voltage. 
Simple transformers are used to step up or down  alternating voltages. A direct voltage must first be  converted to an alternating voltage before its value  can be changed. This adds complexity and cost to  using direct voltages. 
Another benefit of using alternating voltages and  currents is that they can be easily and inexpensively  converted into direct voltage and current. A diode is a  semiconductor device that allows current to flow in  only one direction.When the direction of current flow  changes, the diode acts like an insulator and stops the  current. Two or four diodes can be used to transform  alternating voltages and currents into direct voltages  and currents. This process is referred to as rectifying an  alternating voltage. 
Basic electrical theory is most easily understood  by studying direct voltages and currents. The study of  alternating voltages and currents can become very  complex. The rest of this chapter will discuss only  direct voltages and currents. 

Conductors, Insulators,  and Semiconductors 
A copper wire is an example of a conductor. A conductor  is a material that has electrons that can easily  move.Metals are very good conductors. Copper is used  to make most of the wires we use because it has high  conductance and is relatively inexpensive. Aluminum  was used in the 1950s to make wires for our homes  because it was less expensive than copper; however, it  is not as good a conductor. 
An insulator is a material whose electrons do not  move freely. Glass, rubber, wood, and porcelain are all  examples of insulators. Insulators are used to prevent  the flow of current. 
A semiconductor is a material that conducts less  than a metal conductor but more than an insulator. Silicon  is the most recognized semiconductor. Most  transistors, diodes, and integrated circuits are produced  from semiconductor materials such as silicon or  germanium. 

Resistance 
Resistance is the opposition to current. A copper wire  has very little resistance; therefore it is a good conductor. 

Insulators have a large resistance. The symbol for  resistance is R. Resistance is measured in ohms. The  symbol for ohms is the Greek letter omega, O. The  schematic symbol for resistance is: 

A good copper wire has a resistance of about onehundredth  of an ohm, or 0.01 O per foot. For comparison,  the resistive heating element used in a  medium-size hair dryer has a resistance of about 14 O. 

Resistors are fabricated using many different  materials. The most common types of resistors are  wire-wound resistors, carbon-composition resistors,  and film resistors. Wire-wound resistors are generally  used in high-power applications. Carbon resistors are  the most common. They are used in most electronic  circuits due to their low cost. Carbon resistors can’t typically  be built with an exact resistance value. Film resistors  are used when a more exact resistance is needed. 

Resistors are easily built with resistance values from 0.01 O to many millions of ohms. 

Analog Electrical Circuits 

All electrical circuits have the three following  components: 
1. A potential difference or voltage. 
2. A closed path for current to flow from one side of  the potential difference to the other. 
3. Resistance, which is often referred to as a “load.” 

Ohm’s law defines the relationships between voltage,  current, and resistance in a simple electrical circuit. 
 

Ohm’s law states that:  potential difference (or voltage) = 

The resistor's current I in amps (A) is equal to the resistor's voltage V in volts (V) divided by the resistance R in ohms (Ω): V is the voltage drop of the resistor, measured in Volts (V).

Series Resistance Circuits 
Multiple resistance elements may be used in an electric  circuit. An example of this type of circuit is the series  resistance circuit, as represented schematically below: 
R1 and R2 are both in the same current path, providing  more total resistance than a single resistance element. 
It is crucial to remember, however, that in a series  resistance circuit, the current is the same everywhere in  the circuit. In other words, the current flowing through 
R1 is the same as the current through R2. The total circuit  resistance is the sum of the resistance of each individual resistance element. 

Parallel Resistance Circuits 
A parallel resistance circuit has two or more loads connected  across a single voltage source. An example of this  is plugging your coffee pot and toaster into the same  electric outlet. Consider the circuit below, where R1 is  the coffee pot and R2 is the toaster. 
The voltage across each resistor of a parallel resistance  circuit is the same. On the other hand, the current  through each resistor of a series resistance circuit is the  same. The current through each resistor in a parallel  circuit may be different, depending on the resistance of  the loads. The total current of the circuit is the sum of  the current through each resistor. 
IT = I1 + I2 

Electrical Power 
The measurement of power (P) should be familiar to  everyone. Light bulbs are used according to their  wattage. Electrical power is measured in watts (W). A  watt is defined to be the work done in one second by  one volt to move one coulomb of charge. It is written  mathematically: 

P = I × V. P = power, I or J

Miscellaneous Electrical Components 

Capacitors 
Most practical circuits contain devices other than voltage  sources, resistors, and wires. Capacitors, for  instance, are widely used. A capacitor is an electrical  device that can store electrical charge. A capacitor’s  function is limited to AC circuits. A common application  for capacitors is building filter circuits to protect  appliances from voltage spikes. The symbol for a capacitor  (C) is similar to a voltage source. 

Fuses 
Fuses are used to protect almost every electrical item  we use. A fuse is typically a small piece of wire that  will burn up and stop conducting electricity when  too much current is forced to flow through it. Fuses  are rated to blow at a given current, up to a maximum  voltage. For example, a typical fuse in a television  may be rated to blow, or open, at 3.0 amperes at  any voltage up to 120 volts to protect the television  from currents over 3 amperes and voltages over 120 
V. An ideal fuse has zero resistance of its own and  opens instantly when excess current flows. Some  fuses are designed to allow a large current surge to  safely flow for a small period of time. This is important  because many appliances and motors have what  is called an in-rush current surge. A “slo-blo” fuse  will allow a large current to flow for a few seconds  before opening. 

Switches 
Switches are used to break a circuit  path to stop current flow to a load, such as a lightbulb. 
There are many types of switches, depending on the  application. The most common switches are singlepole- single-throw and double-pole-double-throw  switches. The dial used to turn the channel on older televisions  is a called a rotary switch. A rotary switch  opens and closes contacts when it is turned. 
V = 120 V R = 6  

Electronic Manufacturing  and Testing 
A common workshop will have most of the tools  needed to work on electrical equipment. Pliers, screwdrivers,  wire cutters, and wrenches are all needed. In  addition, a few specialty tools are required. For  instance, a wire stripper is a very useful tool. It is used  to remove the insulation from a wire in preparation for  joining the wire to a circuit element. 

Solder 
Solder and a soldering iron are used to physically connect  most circuit components. Solder is a metal alloy  usually containing almost equal amounts of tin and  lead. Solder is usually specified to be either 40 percent  tin and 60 percent lead, 50 percent each, or 60 percent  tin and 40 percent lead. The latter mixture does the best  soldering job because it melts the easiest, flows the  best, and hardens the fastest.However, it is more expensive  than the other mixtures. A soldering iron melts solder  by heating it to 500 or 600 degrees Fahrenheit; the  solder is fused to the metal leads of the electronic components  and wires as it cools to permanently bond  them together. A joint that has been properly soldered  will appear shiny and smooth. A flux must also be used  when soldering to remove oxidation from the components  to be joined. The flux is typically contained in the  solder. One must be careful to not use acid flux when  joining electronic components because the acid will  eventually corrode the solder joint. A rosin flux is preferred  for electronic uses. 

Wires and Printed Circuit Boards 
Wires have historically been used to connect the components  of a circuit. Today’s modern technology has replaced most wires with printed circuit boards  (PCBs). Printed circuit boards are thin, typically fiberglass  boards with electronic components soldered to  them and copper circuit paths, called traces, that  replace discrete wires. Complex circuits can be built  using multi-layer PCBs. The copper traces can be sandwiched  and laminated between more boards. Typical  multi-layer circuit boards may have three to seven layers  of circuit paths. If you take the top off a computer  or television you will see large and small PCBs and relatively  few discrete wires.Wires are mostly used today  to join PCBs to connectors. 

Mastering Zeros 
The numbers used for circuit analysis are often either very large or very small. Writing out all the zeroes before  or after the decimal point can be extremely tedious. Prefixes are used to simplify the writing out of all the zeros. 

For example a billion words can be written as any of the following: 
1,000,000,000 words  or 
1,000 million words  or 
1 x 109 words  or better yet 
1G words 

Prefixes that are typically used to simplify measurement terminology. 
prefix - symbol -multiplier  
giga G 10^9  
mega M 10^6  
kilo k 10^3  
milli m 10^-3 
micro u 10^-6 
nano n 10^-9 
pico p 10^-12

Testing Instruments 
The testing of electronic circuits requires a few specialized  test instruments. Measuring basic DC circuit  parameters can be accomplished with the following  instruments: 
- ammeter: measures currents 
- ohmmeter: measures resistance 
- voltmeter: measures voltage 
Voltage is the easiest parameter to test. A voltmeter  can easily be connected across the device being tested  at any point in the current. An ammeter must be connected  in series to give a true indication of the current  in the circuit. An ohmmeter is typically used on an  unpowered device to measure its resistance. Many  times the device being measured must be completely  removed from the circuit to get an accurate resistance  measurement. Power in a circuit is typically calculated  after measuring the voltage and current. 
Testing AC circuits and digital circuits requires  much more complex and expensive test equipment. 
An oscilloscope is used to display AC and complex  voltage waveforms. It is an indispensable tool for  analyzing most of the circuits found in today’s electronic  products. The test equipment needed to test  tomorrow’s circuits will become more and increasingly  specialized with the continued rapid growth of  technology. 

Radio 
The radio was invented by Guglielmo Marconi in the  late 1800s. 
The theory behind radio is simple; however, the  experience needed to fully understand radio may take  years of study to develop. 
The voice or music signal is combined with a carrier  wave and fed into an amplifier and then to an antenna. 
The antenna transmits the combined signal into the air. 
The receiving antenna catches the weak signal out of  the air and sends it to an amplifier. The signal is amplified,  and then the carrier wave is removed, leaving the  original voice or music signal intact. The original signal  can then be amplified again and listened to through  a speaker. 
Radio: communication between two or more  points using electromagnetic waves as the  transmission medium. 
Radio communication was first used on ships to communicate  at sea. The importance of radio was proven  when assistance was requested by the Titanic when it  was sinking. Radio communication is not limited to the 
AM and FM radios we listen to. Television and cellular  phones are also examples of radio communication.