CHAPTER 4The Electronic Computer Age

ELECTRONICS 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.

THE SMALLEST PIECES OF OUR WORLD 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.

THE SMALLEST PIECES OF OUR WORLD… 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.

ATOMS… 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.

WHAT DOES THAT MEAN? 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.

ELECTRIC CURRENT 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.

ELECTRONS 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.

ELECTROMOTIVE 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.

BATTERY

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.

ELECTRICAL CURRENT FLOW

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.

RESISTANCE 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.

ELECTRONIC COMPONENTS AND CIRCUITS 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.

RESISTOR 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.

SEMICONDUCTORS 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.

TRANSISTOR 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.

OTHER COMPONENTS 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.

PRINTED CIRCUITS, P. 96 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.

WIRES CAN’T TOUCH! 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…

PRINTED CIRCUIT BOARD 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.

CONT’D… 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.

INTEGRATED CIRCUITS 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.

CHIP P. 97 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.

COMPUTERS… 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.

ANALOG AND DIGITAL CIRCUITS 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.

ANALOG CIRCUIT 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.

DIGITAL CIRCUITS 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.

WHAT IS A COMPUTER SYSTEM? 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.

COMPUTERS TODAY 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)

DATA 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?

THE COMPUTER PROCESSOR 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.

PROCESSOR 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.

MEMORY P. 102 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.