1. The Electronic Computer Age

2.  The use of electronics has completely changed our world in the last hundred years.  The electric light has extended our day.  Electric appliances in the kitchen allow us to keep our food longer and prepare it more quickly.  Other electric appliances have reduced the amount of time we spend on work, giving us more free time.  Electronic entertainment has changed the way we spend our free time.

3.  All materials are made up of tiny particles called atoms. Materials made up of only one kind are called elements.  Iron and carbon are examples of elements.  Only 103 elements are known to exist.  An atom is the smallest part of an element that can exist and still have all the properties of that element.  Atoms are so small that you cannot see them, even with the most powerful optical microscope.

4.  Atoms of different kinds may be combined to make materials called compounds.  When a compound is formed from two or more elements, it has properties all its own.  It may be nothing like the elements it is made of.  For example, sodium, a poisonous metal that reacts violently when it touches water, makes a compound with chlorine, a poisonous gas. The compound sodium chloride, or common table salt.

5.  Atoms are made up of even smaller particles. These particles do not have the properties of the element.  They have their own properties. Atoms have a center part called a nucleus.  The nucleus is made up of protons and neutrons. Smaller particles called electrons circle the nucleus very rapidly.

6.  The number of protons in an atom determines the kind of element it is.  For example, atoms with 13 protons are aluminum atoms.  Atoms with 29 protons are copper.  Protons and electrons have electric charges.  Protons are positive and electrons are negative.  Neutrons have no charge.  In most natural atoms, the number of protons equals the number of electrons.  The positive charges equal the negative charges. The atom, therefore, has no charge.

7.  In some atoms, the electrons are held tightly to the atom. In other atoms, some of the electrons are easily pulled away. They move from one atom to another.  Materials whose atoms give up some electrons easily are called conductors.  Materials that hold tightly to their electrons are called insulators.  In a conductor, electrons can move from one atom to another.  In an insulator, each atom’s electrons are tightly held, and electrons are not free to move between atoms.

8.  Electrons can flow through a thin wire or a piece of solid material, or even through the air, as in a lightning bolt.  The flow of electrons is called current.  The measure of current flow is ampere or amp.  One amp is equal to about six billion electrons flowing past a point in one second.

9.  Electric current is the flow of electrons through a conductor.  When you want to move a chair, you have to push on it. You have to exert a force. In the same way, to get a current to flow, a force has to be applied.  This force, called an electromotive force, is measured in volts.  Without voltage, no current will flow.

10.  A battery provides electromotive force.  A battery has a positive terminal an a negative terminal. When the terminals are connected to the opposite ends of a wire, electrons start moving.  They are attracted to the positive terminal and repelled from the negative one.  This sets up a current, or flow of electrons.

11.  Ohm’s Law is an equation that describes the flow of electrical current.  Current (amps) = Voltage _______________ Resistance (ohms)  If voltage gets larger, current gets larger. If resistance gets larger, current gets smaller.

12.  Some conductors are better than others.  For a given voltage (force), more current flows through a good conductor than a poor one.  Resistance is the opposition to a flow of current.  It is the measure of how good a conductor is.  A material with high resistance is a poor conductor.  A material with low resistance is a good conductor. The unit of resistance is the ohm.

13.  Electronic components, or parts, control the flow of electricity (electrical current). They carry out many useful tasks.  Components are connected together in different ways to form circuits.  A circuit is a group of components connected together to do a specific job.  Designers show plans for circuits using drawings called schematics. In these drawings, each component has its own symbol.

14.  One of the simplest components is the resistor.  A resistor has a known resistance value.  It is used to control current flow.  Resistors come in a wide range of values, from less than one ohm to tens of millions of ohm.  On many resistors, color-coded bands indicate the resistance in ohms.

15.  Semiconductors are materials that are neither good insulators or good conductors.  The most common semiconductor material is silicon.  One kind of component made using semiconductors is the diode.  A diode lets current flow in one direction but not the other.

16.  One of the most important electronic components today is the transistor, which was invented in 1947.  A transistor is a resistor that lets a small amount of current control the flow of a much larger amount of current.  Transistors are used to control electric motors. They can also be used to control the storage of a small electric charge used to represent information, as in a computer.  The transistor is very small.

17.  Other components are like transistors and resistors.  A thermistor has a resistance that changes with the temperature.  Thermistors can be used to make electronic thermometers.  They can also be used as part of the control system of refrigerators or ovens.  A photoresistor has a resistance that changes with the amount of light hitting it.  Photoresistors can be used to turn on lights when it gets dark. They also can be used to measure light.

18.  Circuits are groups of components connected together to do a specific job.  Components are often connected by wires.  Soldering is a method of joining two wires together.  A metal solder is melted on them, forming a connection.  Solder has low resistance and therefore makes a good connection.

19.  Care is taken to make sure wires in a circuit do not accidentally touch.  This would set up an unintended flow of current (a short circuit). To prevent this, wires often have a covering of insulation. The insulation prevents short circuits.  Early circuits used large components that were connected to each other by several wires.  Each wire was soldered by hand.  Components became smaller over the years, and hard to solder.  Also, a way was needed to make the same circuit over again without mistakes…

20.  The printed circuit board solved both problems.  A printed circuit board is a thin board made of an insulating material, such as fiberglass.  On one or both sides, a thin layer of a good conductor, often copper, is plated right on the board.  Patterns etched in the copper form paths for electricity.  Holes for mounting components are drilled in the board.

21.  The components are then soldered to the conducting paths on the board.  The conducting paths are photographically placed on the board, so many boards can be made with exactly the same circuit.  Once the components are mounted on the board, they can all be soldered at once by an automatic soldering machine.

22.  One of the most important inventions of the twentieth century is the integrated circuit.  An integrated circuit provides a complete circuit on a tiny bit of semiconductor.  Integrated circuits are often less than one- tenth of an inch long by one-tenth of an inch wide.  This chip contains components and conducting paths.

23.  A chip is designed by an engineer, who makes a drawing of it several hundred times larger than it will be.  The drawing is photographically reduced, forming a mask.  The mask is used to put patterns on a wafer of semiconductor material.  Many identical circuits are made at once on a round wafer several inches across.

24.  Computers are built using large integrated circuits.  Computers that took up rooms of space twenty years ago now fit on a desk top or on a cell phone because of integrated circuits.  Chips have replaced large, bulky circuits in many other systems as well.

25.  Information can be represented by electricity in several ways.  One way is to have a voltage change based on the information it represents.  A voltage could represent a person’s speech.  It would get larger as the person talked louder.  In this case, the voltage is the analog of, or similar to, the person’s speech.  It is called an analog special.

26.  An electronic circuit that works with analog signals is called an analog circuit.  Voltages in such a circuit change smoothly, as do the things they represent, such as a person’s voice.  Sometimes information must be very accurate or must be sent over long distances.  Under these conditions, analog circuits are not good enough…  In these cases, digital technology is used.

27.  In digital circuits, information is first coded into a series of 0s and 1s.  A voltage above a certain value is coded as a 1.  A voltage below that value is coded as a 0.  Each 1 or 0 is called a bit, short for binary digit.  Binary refers to the number system that has only two numbers, 0 and 1.

28.  A computer does its work according to a list of instructions, called a program.  The program can be changed at any time.  A computer is therefore a general-purpose tool.  A programmer makes it do a given job by providing instructions, but can change the instructions to make it do a different job – this is called program control.

29.  Most of today’s computers are digital, using 1s and 0s to represent information.  Any number can be represented by a binary number, a group of 1s and 0s.  Bits are organized into groups of 8 to make them easier to work with.  These groups of 8 bits are called bytes.  Each byte can represent one of 256 different characters (numbers, letters, punctuation, or other information)

30.  Data can be represented by bytes, kilobytes (one kByte = one thousand bytes), or megabytes (one Mbyte = one million bytes)  So how many bytes would 4 kBytes represent?

31.  All computers have some parts in common.  The first is the processor.  The processor controls the flow of data, its storage, and what the computer does with the data.  The processor reads the program and changes the instructions into actions.  The actions might be able to add two numbers or store a number or letter.

32.  The power of a processor refers to how fast it is.  Personal computers can carry out hundreds of thousands of instructions in a second.  Large business computers can carry out millions of instructions per second (MIPS). Very fast computers can handle hundreds of millions of instructions per second.

33.  The place where the program is stored is called the memory.  The memory also stores the information being worked on.  Most computers use integrated circuit memory circuits.  A tiny chip can store more than one million characters.