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Electricity
So what is Electricity?
Easier - Electricity is a form of energy produced by the movement
of electrons. Electricity is electrical power or an electric current.
This form of energy can be sent through wires in a flow of tiny
particles. It is used to produce light and heat and to run motors.
Harder - Electricity is a basic feature of all matter, of everything
in the universe. Electrical force holds atoms and molecules
together. Electricity determines the structure of every object that
exists. Together with magnetism, it causes a force called
electromagnetism, a fundamental force of the universe.
TYPES OF ELECTRICITY
(BASED ON FLOW OF
ELECTRONS)
Direct current, abbreviated "DC". This is the type of electricity
that is produced by batteries, static, and lightning. A voltage is
created, and possibly stored, until a circuit is completed. When it
is, the current flows directly, in one direction.
An idealized 12 V DC current. The voltage is
considered positive because its potential is
measured relative to ground or the zeropotential default state of the earth.
(This diagram drawn to the same scale as the
AC diagram below.)
Alternating current, or "AC". This is the electricity that you get from your house's
wall and that you use to power most of your electrical appliances. Alternating current
is harder to explain than direct current. The electricity is not provided as a single,
constant voltage, but rather as a sinusoidal (sine) wave that over time starts at zero,
increases to a maximum value, then decreases to a minimum value, and repeats. A
representation of an alternating current's voltage over time is shown in the diagram
below.
The most common AC waveform is a sine (or
sinusoidal) waveform.
Why does standard electricity come only in
the form of alternating current?
There are a number of reasons, but one of the
most important is that a characteristic of AC is
that it is relatively easy to change voltages
from one level to another using a transformer,
while transformers do not work for DC.
Another reason is that it may be easier to
mechanically generate alternating current
electricity than direct current.
PCs use only direct current, which means that the
alternating current provided by your utility must be
converted to direct current before use. This is the
primary function of your power supply.
Conductors and Insulators
In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most nonmetallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them. "Conductor"
implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their
electrons tightly and are insulators. In copper, the valence electrons are essentially free and strongly repel each other. Any external
influence which moves one of them will cause a repulsion of other electrons which propagates, "domino fashion" through the
conductor.
Simply stated, most metals are good electrical conductors, most nonmetals are not. Metals are also generally good heat
conductors while nonmetals are not.
Here are a few common examples of
conductors and insulators:
•Conductors:
•silver
•copper
•gold
•aluminum
•iron
•steel
•brass
•bronze
•mercury
•graphite
•dirty water
•Concrete
•Insulators:
•glass
•rubber
•oil
•asphalt
•fiberglass
•porcelain
•ceramic
•quartz
•(dry) cotton
•(dry) paper
•(dry) wood
•plastic
•air
•diamond
•pure water
It must be understood that not all conductive
materials have the same level of conductivity, and
not all insulators are equally resistant to electron
motion. Electrical conductivity is analogous to the
transparency of certain materials to light: materials
that easily "conduct" light are called "transparent,"
while those that don't are called "opaque." However,
not all transparent materials are equally conductive
to light. Window glass is better than most plastics,
and certainly better than "clear" fiberglass. So it is
with electrical conductors, some being better than
others.
For instance, silver is the best conductor in the "conductors" list, offering easier
passage for electrons than any other material cited. Dirty water and concrete are also
listed as conductors, but these materials are substantially less conductive than any
metal.
It should also be understood that some materials experience changes in their electrical
properties under different conditions. Glass, for instance, is a very good insulator at
room temperature, but becomes a conductor when heated to a very high
temperature. Gases such as air, normally insulating materials, also become conductive
if heated to very high temperatures. Most metals become poorer conductors when
heated, and better conductors when cooled. Many conductive materials become
perfectly conductive (this is called superconductivity) at extremely low temperatures.
While the normal motion of "free" electrons in a conductor is random,
with no particular direction or speed, electrons can be influenced to
move in a coordinated fashion through a conductive material. This
uniform motion of electrons is what we call electricity, or electric
current. To be more precise, it could be called dynamic electricity in
contrast to static electricity, which is an unmoving accumulation of
electric charge. Just like water flowing through the emptiness of a pipe,
electrons are able to move within the empty space within and between
the atoms of a conductor. The conductor may appear to be solid to our
eyes, but any material composed of atoms is mostly empty space! The
liquid-flow analogy is so fitting that the motion of electrons through a
conductor is often referred to as a "flow."
A noteworthy observation may be made here. As each electron
moves uniformly through a conductor, it pushes on the one ahead
of it, such that all the electrons move together as a group. The
starting and stopping of electron flow through the length of a
conductive path is virtually instantaneous from one end of a
conductor to the other, even though the motion of each electron
may be very slow. An approximate analogy is that of a tube filled
end-to-end with marbles:
The tube is full of marbles, just as a conductor is full of free
electrons ready to be moved by an outside influence. If a
single marble is suddenly inserted into this full tube on the
left-hand side, another marble will immediately try to exit the
tube on the right. Even though each marble only traveled a
short distance, the transfer of motion through the tube is
virtually instantaneous from the left end to the right end, no
matter how long the tube is. With electricity, the overall effect
from one end of a conductor to the other happens at the
speed of light: a swift 186,000 miles per second!!! Each
individual electron, though, travels through the conductor at a
much slower pace.
If we want electrons to flow in a certain direction to a certain place, we must
provide the proper path for them to move, just as a plumber must install piping
to get water to flow where he or she wants it to flow. To facilitate this, wires are
made of highly conductive metals such as copper or aluminum in a wide variety
of sizes.
Remember that electrons can flow only when they have the opportunity to
move in the space between the atoms of a material. This means that there can
be electric current only where there exists a continuous path of conductive
material providing a conduit for electrons to travel through. In the marble
analogy, marbles can flow into the left-hand side of the tube (and, consequently,
through the tube) if and only if the tube is open on the right-hand side for
marbles to flow out. If the tube is blocked on the right-hand side, the marbles
will just "pile up" inside the tube, and marble "flow" will not occur. The same
holds true for electric current: the continuous flow of electrons requires there
be an unbroken path to permit that flow. Let's look at a diagram to illustrate how
this works:
A thin, solid line (as shown above) is the conventional symbol
for a continuous piece of wire. Since the wire is made of a
conductive material, such as copper, its constituent atoms
have many free electrons which can easily move through the
wire. However, there will never be a continuous or uniform
flow of electrons within this wire unless they have a place to
come from and a place to go. Let's add an hypothetical
electron "Source" and "Destination:"
Now, with the Electron Source pushing new electrons into the
wire on the left-hand side, electron flow through the wire can
occur (as indicated by the arrows pointing from left to right).
However, the flow will be interrupted if the conductive path
formed by the wire is broken:
Since air is an insulating material, and an air gap separates the two pieces of wire, the
once-continuous path has now been broken, and electrons cannot flow from Source
to Destination. This is like cutting a water pipe in two and capping off the broken ends
of the pipe: water can't flow if there's no exit out of the pipe. In electrical terms, we
had a condition of electrical continuity when the wire was in one piece, and now that
continuity is broken with the wire cut and separated.
If we were to take another piece of wire leading to the Destination and simply make
physical contact with the wire leading to the Source, we would once again have a
continuous path for electrons to flow. The two dots in the diagram indicate physical
(metal-to-metal) contact between the wire pieces:
Now, we have continuity from the Source, to the newly-made
connection, down, to the right, and up to the Destination. This is
analogous to putting a "tee" fitting in one of the capped-off pipes
and directing water through a new segment of pipe to its
destination. Please take note that the broken segment of wire on
the right hand side has no electrons flowing through it, because it
is no longer part of a complete path from Source to Destination.
It is interesting to note that no "wear" occurs within wires due to
this electric current, unlike water-carrying pipes which are
eventually corroded and worn by prolonged flows. Electrons do
encounter some degree of friction as they move, however, and
this friction can generate heat in a conductor. This is a topic we'll
explore in much greater detail later.
Static and Dynamic
Definition
- In general, dynamic means energetic, capable of action
and/or change, or forceful,
while static means stationary or fixed. In computer
terminology, dynamic usually means capable of action
and/or change, whilestatic means fixed. Both terms can be
applied to a number of different types of things, such as
programming
languages
dynamic and
static (or components of programming
languages), Web pages, and application programs.When a
Web page is requested (by a computer user clicking a
hyperlink or entering a URL), the server where the page is
stored returns the HTMLdocument to the user's computer
and the browser displays it.
On a static Web page, this is all that happens.
The user may interact with the document
through clicking available links, or a small
program (an applet) may be activated, but the
document has no capacity to return information
that is not pre-formatted. On a dynamic Web
page, the user can make requests (often
through a form) for data contained in
a database on the server that will be
assembled on the fly according to what is
requested.
For example the user might want to find out
information about a theatrical performance, such
as theater locations and ticket availability for
particular dates. When the user selects these
options, the request is relayed to the server using
an intermediary, such as an Active Server Page
(ASP) scriptembedded in the page's HTML. The
intermediary tells the server what information to
return. Such a Web page is said to be dynamic.
A set of HTML capabilities are provided that help
a designer create dynamic Web pages. This set
of capabilities is generally known as dynamic
HTML.
There are dynamic and static programming
languages. In a dynamic language, such
as Perl or LISP, a developer can
create variables without specifying their type.
This creates more flexible programs and can
simplifyprototyping and some objectoriented coding. In a static programming
language, such as C or Pascal, a developer
must declare the type of each variable before
the code is compiled, making the coding less
flexible, but also less error-prone.
Digital vs. Analog Signal
What is a Signal?
Plain and simple, a signal is the transmission of data. We deal with
signals constantly during the span of our lives. We interact with
signals from music, power lines, telephones, and cellular devices.
This means the use of antennas, satellites, and of course wires.
In "computer land" signals are very important. Anyone that uses a
computer should know how the machine transforms data into
signals that other computers and devices can understand. In many
cases, knowing how signals work will help you solve some kind of
technical problem over the span of your life.
Analog Waveforms
Analog signals were first used in the 1800's. They were used in conjunction
with copper telephone lines to transmit conversations. This involved using 2
conductors for each line (send and receive). As technology progressed an
increasing number of people started using the telephone making analog signals
too expensive and troublesome to maintain. This was due to the way the analog
signals work. See the images below:
Now notice that the signal has picked up
"noise." Noise is simply an unwanted
electrical or electromagnetic energy that
degrades the quality of a signal. The signal
level crosses over the X and Y limits and
has now become degraded and hard for the
device on the receiving end to interpret.
Noise is sometimes called "distortion" or
"clipping."
As signals travel across a wire, certain factors will add
more "noise" to the signal. These factors can include: air
conditioning units, fluorescent lights, magnetic fields,
etc. There are methods of separating or "filtering" noise
from analog signals. However, most of these methods are
not accurate, or are devices that transform the signals
from analog to digital and back to analog. For these
reasons, the use of digital signaling is used to provide a
better delivery method.
Digital Waveforms
The physics of digital signals are different than analog signals because they are discrete waveforms.
Between the minimum X and the maximum Y, there is a limit on how high the voltage will increase or
decrease. See the images below:
Notice that the signal takes 2 basic forms: on (with a value of 1) and off (with a value or 0). Obviously digital
signals are more complicated that this, but being an article on the basics of signals, you get the general idea.
Notice that the signal is very uniform in composition.
Here, we see the main advantage of digital over analog. Since the signal is very uniform, noise
has not severely altered its shape or amplitude. The digital signal shows a far less change to the
actual waveform than the previous analog signal. They are both shown below for a close
comparison.
What Does This Have To Do With Computers?
Computers use digital signals to send and receive data. Although digital signals can only be in the
state 1 (on) and 0 (off), complicated combinations of these two values are used to send/receive data.
Think of this example:
Using only binary (values 1 and 0), we can create a string of values that is interpreted by a computer
to be something more meaningful. For instance, the value 11000110 00110101 10010011 00101101 is
interpreted to equal 198.53.147.45 in decimal format.
Conclusion
In conclusion, the strength of using a digital system over analog is clear.
Digital signals are easier to transmit and offer less room for errors to
occur. This leads to accurate data transmission that in turn leads to faster
transmission rates and better productivity.
Resistor
A resistor is a two-terminal electronic component that
opposes an electric current by producing a voltage drop
between its terminals in proportion to the current.
Resistors are used as part of electrical networks and
electronic circuits.
The mathematical relationship between the electrical
resistance (R) of the resistor, the voltage drop (V) across
the resistor, and the current (I) flowing through the
resistor is expressed by the following equation, known as
Ohm's law:
V = IR.
Colour code
How can the value of a resistor be worked out from the colours of the bands? Each
colour represents a number according to the following scheme:
The first band on a resistor is interpreted as the FIRST DIGIT of the resistor value. For the
resistor shown below, the first band is yellow, so the first digit is 4:
Numb
er
Colour
0
black
1
brown
2
red
3
orange
4
yellow
5
green
6
blue
7
violet
8
grey
9
white
Ohms Law
George Ohms (1789 - 1854) found that Current flowing through a component is related to its Resistance and the Voltage across it.
He produced the formula:-
Voltage(in volts) = Current (in amps) x Resistance (in ohms)
V=IxR
I = V/R
R = V/I
The second band gives the SECOND DIGIT. This is a violet band,
making the second digit 7. The third band is called the
MULTIPLIER and is not interpreted in quite the same way. The
multiplier tells you how many noughts you should write after the
digits you already have. A red band tells you to add 2 noughts. The
value of this resistor is therefore 4 7 0 0 ohms, that is, 4 700 , or
4.7
. Work through this example again to confirm that you
understand how to apply the colour code given by the first three
bands.
The remaining band is called the TOLERANCE band. This indicates
the percentage accuracy of the resistor value. Most carbon film
resistors have a gold-coloured tolerance band, indicating that the
actual resistance value is with + or - 5% of the nominal value. Other
tolerance colours are:
Toleran
ce
Colour
±1%
brown
±2%
red
±5%
gold
±10%
silver
When you want to read off a resistor value, look for the tolerance band, usually gold, and hold the resistor with the tolerance
band at its right hand end. Reading resistor values quickly and accurately isn't difficult, but it does take practice!
Axial-lead resistors on tape. The tape is removed during assembly before the leads are formed and the part is inserted into
the board.
Three carbon composition resistors in a 1960s valve radio.
Electronic components – resistor
Capacitor
. A capacitor (formerly known as condenser) is a passive electronic component
consisting of a pair of conductors separated by a dielectric (insulator). When there is a
potential difference (voltage) across the conductors a static electric field develops in
the dielectric that stores energy and produces a mechanical force between the
conductors. An ideal capacitor is characterized by a single constant value, capacitance,
measured in farads. This is the ratio of the electric charge on each conductor to the
potential difference between them.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass, in filter networks, for smoothing the output of
power supplies, in the resonant circuits that tune radios to particular frequencies and
for many other purposes.
The effect is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are
often called "plates", referring to an early means of construction. In practice the dielectric between the plates passes a
small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the
conductors and leads introduce an equivalent series resistance
Capacitor
Modern capacitors, by a cm rule
Type
Invented
Passive
Ewald Georg von Kleist
(October 1745)
A typical electrolytic capacitor
Electronic symbol
Capacitor types
•Metal film: Made from high quality polymer foil (usually polycarbonate,
polystyrene, polypropylene, polyester (Mylar), and for high quality
capacitors polysulfone), with a layer of metal deposited on surface. They
have good quality and stability, and are suitable for timer circuits. Suitable
for high frequencies.
•Mica: Similar to metal film. Often high voltage. Suitable for high
frequencies. Expensive.
•Paper: Used for high voltages.
•Glass: Used for high voltages. Expensive. Stable temperature coefficient in
a wide range of temperatures.
•Ceramic: Chips of altering layers of metal and ceramic. Depending on their
dielectric, whether Class 1 or Class 2, their degree of temperature/capacity
dependence varies. They often have (especially the class 2) high dissipation
factor, high frequency coefficient of dissipation, their capacity depends on
applied voltage, and their capacity changes with aging. However they find
massive use in common low-precision coupling and filtering applications.
Suitable for high frequencies.
•Electrolytic: Polarized. Constructionally similar to metal film, but the
electrodes are made of aluminium etched to acquire much higher
surfaces, and the dielectric is soaked with liquid electrolyte. They suffer
from high tolerances, high instability, gradual loss of capacity especially
when subjected to heat, and high leakage. Special types with low
equivalent series resistance are available. Tend to lose capacity in low
temperatures. Can achieve high capacities.
•Tantalum: Like electrolytic. Polarized. Better performance with higher
frequencies. High dielectric absorption. High leakage. Have much better
performance in low temperatures.
•Supercapacitors: Made from carbon aerogel, carbon nanotubes, or
highly porous electrode materials. Extremely high capacity. Can be used
in some applications instead of rechargeable batteries.
Energy storage
A capacitor can store electric energy when disconnected from its
charging circuit, so it can be used like a temporary battery. Capacitors
are commonly used in electronic devices to maintain power supply
while batteries are being changed. (This prevents loss of information
in volatile memory.)
Conventional electrostatic capacitors provide less than 360 joules per
kilogram of energy density, while capacitors using developing
technologies can provide more than 2.52 kilojoules per kilogram[22].
In car audio systems, large capacitors store energy for the amplifier to
use on demand. Also for a flash tube a capacitor is used to hold the
high voltage. In ceiling fans, capacitors play the important role of
storing electrical energy to give the fa
Transistor
Assorted transistors.
A transistor is a semiconductor device that uses a small amount of voltage or electrical current to control a larger
change in voltage or current. Because of its fast response and accuracy, it may be used in a wide variety of applications,
including amplification, switching, voltage stabilization, signal modulation, and as an oscillator. The transistor is the
fundamental building block of both digital and analog circuits—the circuitry that governs the operation of computers,
cellular phones, and all other modern electronics. Transistors may be packaged individually or as part of an integrated
circuit chip, which may hold thousands of transistors in a very small area
Types
Transistors are categorized by:
•Semiconductor material: germanium, silicon, gallium arsenide, silicon carbide
•Structure: BJT, JFET, IGFET (MOSFET), IGBT, "other types"
•Polarity: NPN, PNP, N-channel, P-channel
•Maximum power rating: low, medium, high
•Maximum operating frequency: low, medium, high, radio frequency (RF),
microwave (The maximum effective frequency of a transistor is denoted by the
term fT, an abbreviation for "frequency of transition." The frequency of
transition is the frequency at which the transistor yields unity gain).
•Application: switch, general purpose, audio, high voltage, super-beta,
matched pair
•Physical packaging: through hole metal, through hole plastic, surface mount,
ball grid array
Thus, a particular transistor may be described as: silicon, surface mount, BJT,
NPN, low power, high frequency switch.
Usage
In the early days of transistor circuit design, the
bipolar junction transistor (or BJT) was the most
commonly used transistor. Even after MOSFETs
became available, the BJT remained the transistor of
choice for digital and analog circuits because of their
ease of manufacture and speed. However, the
MOSFET has several desirable properties for digital
circuits, and major advances in digital circuits have
pushed MOSFET design to state-of-the-art.
MOSFETs are now commonly used for both analog
and digital functions.
Computers
The "first generation" of electronic computers
used vacuum tubes, which generated large
amounts of heat and were bulky, and unreliable.
The development of the transistor was key to
computer miniaturization and reliability. The
"second generation" of computers, through the
late 1950s and 1960s, featured boards filled with
individual transistors and magnetic memory
cores. Subsequently, transistors, other
components, and their necessary wiring were
integrated into a single, mass-manufactured
component: the integrated circuit. Transistors
incorporated into integrated circuits have
replaced most discrete transistors in modern
digital computers.
Close-up of a transistor on a mother board
Group members:
Maricris Arahan
Rochelle Babriera
Desarie Barbuco
Jerome Barrera
Elaine Bautista