electricity354

History of discovery of Electricity

2012-09-09T13:00:00.000-07:00

Benjamin Franklin is known as the first person who discovered electricity. Benjamin was born in 1705, he began studying electricity at the beginning of the year 1750an. He was doing research one with kite experiment to prove the existence of a natural power. In 1752 he did experiment by placing a sharp metal tip on the end of a kite string locks fitted.

Benjamin first who discovered the principles of electricity and also give positive and negative electricity. He then published his experiments to prove that lightning is actually electricity by flying a kite in a storm. In his writings, Benjamin Franklin wrote that he was aware of the dangers that can result from the experiments and offer an alternative that proves that lightning is electricity, which is then in the show by using the concept of electrical ground. Not as pictured person that Benjamin experiment done by flying a kite and wait until the kite was struck by lightning. Benjamin uses his kite just to collect electricity from storm clouds.
Experiments to electricity by Benjamin, directing him to the invention, the lightning rod. He wrote that the conductor (electric) with a sharp edge has the ability to draw an electrical charge and has a range of further withdrawals than conductors with a blunt tip. He concluded that this knowledge can be used to protect the house from lightning danger, by putting an iron bar seruncing pointy needles and anti-rust coating, which is directed to the sky, and the legs of iron, attached with wires leading to the ground. This will attract the lightning rod at electric charge cloud to the ground so that the charge is on the cloud is not enough to cause thunder and lightning.
During the years 1750-1850 are found important discoveries about the working principle of such power by Volta, Couloumb, Gauss, Henry, and Faraday.
Ref:
http://electrical-science.blogspot.com/2010/06/history-of-electric-power.html
http://www.ceritakecil.com/tokoh-ilmuwan-dan-penemu/Benjamin-Franklin-15

Preparation Installing Electrical Installation

2012-09-09T12:56:00.000-07:00

Things - things to consider before installing the electrical installation is as follows:
* Plan the home.To determine the location of the Fuse Box / Box MCB, point lights, switches and SC (Stop Contacts / socket) and of course the lines are to be installed electrical installation. This Plan will be helpful for a number of common mistakes to avoid cable channel used due to branching channel lights, switch and SC.
* Equipment installation and equipment.Almost every household has the equipment for electrical installation such as combination pliers, screwdrivers, razor / blades / hacksaw, hammer betel and so we do not need to buy new .. might just have to buy test-pen. This tool is used to download the attached test electrical installations and much needed to repair electrical installations that have been installed. Because it is strongly recommended to have this tool. No need an expensive, important works fine. One more thing that is lighter (preferably a gas lighter cigarette lighter), but if there is no fire from the candles was so. Why yes ..?

* Determine the security being used.Safety is commonly used in electrical installations and building homes is a masing2 fuse and MCB have a different container or place the Fuse Box and Box MCB. Each has advantages and disadvantages. Here's a little description of my experience (not to read the books / literature lhoo ...).

    Fuse Box.
Pros:
  - It has two parts, namely the fuse connected in phase and disconnect switch (either phase or neutral) of the power source (PLN, diesel, etc.).
  - If the fuse is damaged / broken due to short circuit can be improved, so no need to buy a new (standard fuse / common lhoo ..).
   - Price fuse cheaper.Disadvantages:
   - It's hard looking for a fuse box that is used to install a lot of group division. Generally there is only 1 group and 2 group installation.
    - It looks less practical.

    Box MCB.
Pros:
    - Can be used for many plant groups.
    - Looks practical and neater.Disadvantages:
    - Usually only part of a given phase MCB safety of the power source (PLN, diesel, etc.).
    - If you need to replace broken new MCB because it is difficult to fix.
    - Price MCB is much more expensive than fuses.
* Determine the length of cable NYM 3 x 4 mm ² and 6 mm ² cable BC.
   - As described above, NYM cable serves as the connecting cable from the power source (KWH meter PLN or Diesel) so decide wisely which should be the source of power and location of safety boxes. We recommend that you put the two are not far apart (± 50 cm) since the cable is quite expensive.
   - As NYM cables, cable 6 mm ² BC also is quite expensive so it's good grounding rod placement is also not too far from a power source and a safety box is not too long so we bought it. For example usually Electric instatir install grounding rod / grounding perpendicular KWH meters below PLN that required cable BC ± 2 m.
* Determine the type, conductor cross-sectional area, and color wiring required in the installation.
   • Type of cable.Commonly used in the installation of the cable is a type of Him (in cable consists only 1 wrapped solid copper conductor wire insulator) or a type of NYM (cable wrapped in insulation is composed of 2, 3 or 4 wire solid copper conductor). Want more wah longer cables NYY. Here we discuss the use of ITS alone (cheaper), for the use of other cables can customize.
   • Conductor cross-sectional area.This involves the ability of the cable (in short the current carrying capability of the cable to the electric current passing through it). The size is 1.5 mm ², 2.5 mm ², 4 mm ², 6 mm ² ff. Actually the installation is done installing calculations on various factors including the large and determine the type of cable digunakan.Untuk we simply use the cable size 1.5 mm ² (for light line), 2.5 mm ² for the main channel and for the outlet (socket) actual use of the cable can be adjusted with the use of the socket. For those of you who are new will subscribe electricity from the state electricity company a good idea to use a cable 2.5 mm ² for each outlet although you will subscribe to 1300VA power down. What is not too big for wire tu SC? For questions on the realization is clumsy, especially for homes with installed power of 1300 VA down. The answer is still in my mind, sorry can not be published. Maybe next time time yaaa ... maybe .... he ... he ... heee ......
   • Color cable.Cable color can be very, very helpful in the installation and repair of electrical installation, I also highly recommend it. PUIL mensyaratkat black cables for phase (shock), blue for neutral and green striped yellow (many are called yellow stripes) for ground wires. But the author does not require lhoo .. only suggest (it's your home, not the home state / government). According PUIL, it is for uniform installation in Indonesia so no salahmya followed. To make it easier again for those of you who are just learning we added one other colored wires (we take the example of red wire). This cable will offer for connecting from the switch to the lights only.
* Determine the length of cable required.If you have limited financial position, the following is very, very helpful because the biggest expense is the provision of electrical installation wiring installation. The math may be a little difficult for the cloud. Here the authors try to summarize it as simple as possible.
1. Determine the main line display electrical installations before branched (prior connected to a power outlet, switch or light fittings). Do not forget exceeded slightly (approximately 20cm) each have ramification (branch lines connect to both the switch and the SC).
  - The main line of the old electrical installations using 2 cables are wired phase (shock) and neutral wires. But because many household appliances now have the induced currents flowing in the body equipment (eg, refrigerator, computer CPU) so many houses were later added the line cord ground (ground) on the main line that will be connected to the socket. The author highly-highly recommend adding ground wires on the main channel. But if you do not have the equipment causing the induced current, 2 wires enough.
2. Determine the length of the cable to the light fitting. Cables for light fittings are needed two cables. Do not forget exceeded slightly (about 20cm)
3. Determine the length of the cable to the switch. The number of cables required depends on the type of switch. Single switch takes 2 pieces of cable, switch doble takes 3 pieces of cable, and so on. Do not forget exceeded slightly (about 20cm)
4. Determine the length of the cable into the socket. If the cable channel 2 main pieces of the cord into the wall socket is also 2 pieces. But if the main cable channel 3 pieces of the cable outlet is also 3 pieces. Do not forget exceeded slightly (about 20cm)
  - For placement of switches and sockets are contiguous (usually in the bedroom and living room) calculation is the number of cable wires switch plus an amount later reduced terminal 1 piece of cable. Do not bother yaa ...
* Calculate the length of the pipe installation is required.In short-term calculation is the main channel plus the length of the branch line to the outlet or switch. For placement adjacent SC switch and can be used a pipe and then the second N-bownya can be modified to connect. Do not forget to specify the number of L-bow/penyambung pipe elbow (90 degree bend).
* Counts the number of switches, sockets and light fittings.
* Counts the number of In-BOUW doos / home switch or SC (if placement in the wall) and the number of T-doos and Kruis doos which is the main channel connecting the branch channel (switches, sockets).

Capacitance and Uses of Capacitors

2012-09-09T12:52:00.000-07:00

Capacitors

Function

Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values. Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10^-6 (millionth), so 1000000µF = 1F
n means 10^-9 (thousand-millionth), so 1000nF = 1µF
p means 10^-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!
There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.

Polarised capacitors (large values, 1µF +)

Examples: Circuit symbol:

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering. There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.
It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size. Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'.
For example: blue, grey, black spot means 68µF
For example: blue, grey, white spot means 6.8µF
For example: blue, grey, grey spot means 0.68µF

Unpolarised capacitors (small values, up to 1µF)

Examples: Circuit symbol: Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labelling systems!
Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be!
For example 0.1 means 0.1µF = 100nF.
Sometimes the multiplier is used in place of the decimal point:
For example: 4n7 means 4.7nF.

Capacitor Number Code

A number code is often used on small capacitors where printing is difficult:

the 1st number is the 1st digit,
the 2nd number is the 2nd digit,
the 3rd number is the number of zeros to give the capacitance in pF.
Ignore any letters - they just indicate tolerance and voltage rating.

For example: 102 means 1000pF = 1nF (not 102pF!) For example: 472J means 4700pF = 4.7nF (J means 5% tolerance).

Colour Code
Colour	Number
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet	7
Grey	8
White	9

Capacitor Colour Code

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating). For example:
brown, black, orange means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.
For example:
wide red, yellow means 220nF = 0.22µF.

Polystyrene Capacitors

This type is rarely used now. Their value (in pF) is normally printed without units. Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!) so you should use a heat sink (such as a crocodile clip). Clip the heat sink to the lead between the capacitor and the joint.

Real capacitor values (the E3 and E6 series)

You may have noticed that capacitors are not available with every possible value, for example 22µF and 47µF are readily available, but 25µF and 50µF are not! Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy.
To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.
The E3 series (3 values for each multiple of ten)
10, 22, 47, ... then it continues 100, 220, 470, 1000, 2200, 4700, 10000 etc.
Notice how the step size increases as the value increases (values roughly double each time).
The E6 series (6 values for each multiple of ten)
10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc.
Notice how this is the E3 series with an extra value in the gaps.
The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values.

Variable capacitors

Variable Capacitor Symbol

Variable Capacitor
Photograph © Rapid Electronics

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor. Many variable capacitors have very short spindles which are not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to check that a suitable knob is available before ordering a variable capacitor.
Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.

Trimmer capacitors

Trimmer Capacitor Symbol

Trimmer Capacitor
Photograph © Rapid Electronics

Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built. A small screwdriver or similar tool is required to adjust trimmers. The process of adjusting them requires patience because the presence of your hand and the tool will slightly change the capacitance of the circuit in the region of the trimmer!
Trimmer capacitors are only available with very small capacitances, normally less than 100pF. It is impossible to reduce their capacitance to zero, so they are usually specified by their minimum and maximum values, for example 2-10pF.
Trimmers are the capacitor equivalent of presets which are miniature variable resistors.

source : www.kpsec.freeuk.com

ELECTRICITY IS NOT A FORM OF ENERGY

2012-09-09T12:47:00.003-07:00

Many encyclopedias, dictionaries, and textbooks contain very clear statements about the nature of Electricity. They say this:

- Electricity is a type of energy.

- Electric current is a flow of energy.

The above statements are wrong. Yes, electrical energy does exist. However, this energy cannot be called "Electricity," since Coulombs of electricity are very different from Joules of electromagnetic energy. Energy and charge are two different things, so they cannot both be the electricity. It's not too difficult to demonstrate the mistake. Below is a collection of simple facts which show that Electricity, the stuff that flows within copper wires, is not form of energy.

In a simple electric circuit, the electricity flows slowly in a complete circle, while the energy moves differently. The electrical energy flows rapidly across the circuit, going from the source to the load but not returning. The energy does not follow the circular flow of electricity; electricity and electrical energy are two different things. No charges of electricity are gained or lost as the charges circulate within the wires, yet batteries create electrical energy from chemical energy, and light bulbs destroy[1] the electrical energy as they convert it into light. Electrical energy takes a rapid one-way path from battery to bulb and then leaves the circuit as light, while electricity flows slowly around (and around and around) a closed-loop path and none is lost.

If electricity is like water inside a pipe, that's the Hydraulic Analogy. But water is not a form of energy. In hydraulics, the energy travels instantly to all parts of the fluid loop, while the fluid itself moves slowly. Two things are flowing through the pipe: slow fluid and fast energy. Or, suppose that electricity is like a row of billiard balls inside a tube. When you push one billiard ball of electricity into one end, all the balls move forward. The energy travels almost instantly along the column of electricity-balls, while the electricity itself moves slowly. The balls aren't made of energy. And two things are moving through that tube: slow electricity and fast energy.

In a lightbulb, charges of electricity flow through the filament and back out again. None are lost. This electricity enters the light bulb through one wire, and the same amount of electricity leaves through the other wire. Yet the energy doesn't act like this at all; it doesn't flow through. Instad the light bulb uses up the electric energy: the electrical energy flows one-way: into the bulb via both wires and it's all transformed into heat and light. The electrical energy doesn't come back out through the second wire and return to the battery. Two things are flowing: electricity flows in a closed loop, while energy is flowing one-way from source to load.

In an AC system, the charges of electricity move back and forth over a distance shorter than a ten-thousandth of a millimeter. In other words, they sit inside the wires and vibrate. That's what "Alternating Current" or AC is all about. The electricity does not move forward at all (if it did, that would be a direct current or "DC.") Yet while these charges of electricity are wiggling back and forth, at the very same time the electrical energy moves forward rapidly. Only the electricity "alternates." The electrical energy does not; the energy flows continuously forwards as waves.
If this is confusing, consider sound waves which move through collections of air molecules. Electricity is like the air which is vibrating, while the electrical energy is like sound waves which fly through the air. Sound and air are two different things, just as energy and electricity are two different things.

Before I go too far with this, I must admit that I am playing a small trick with words. In the above statements, I am using the word "electricity" in the way scientists have used it since Electricity was first investigated. I am using the word "electricity" to name the stuff that flows inside the wires; where a quantity of electrons is a quantity of electricity, and where a flow of electricity is called "an electric current."
Why is this a trick? It's a trick because most people use the word "electricity" in a totally different way. They begin by defining the word "electricity" to mean electrical energy! Electric companies do this (think of kilowatt-hours of electricity.) So do the science textbooks written for grades K-6. So do many dictionaries and encyclopedias. This causes endless confusion. Physicists try to tell us that the charges of electricity are not energy, and that a flow of charges is not a flow of energy. But then what is an electric current? Under the definition of "electricity" used by all the non-scientists, an electric current IS NOT a flow of electricity!
Huh? Confused? You SHOULD be confused. There's something wrong here.
Note: my above statements about electricity and energy would be accepted by most scientists throughout history, including Ben Franklin, Michael Faraday, James C. Maxwell and Robert Millikan. I'm using the word electricity in the same manner as they did: electricity is the positive and negative "stuff" that's found in all electrons and protons. It is the "substance" that flows along inside of the wires. When it flows, these scientists would call it a "current of electricity." They'd say that any charged object has a "charge of electricity," and that electrons and protons are "particles of electricity."
Without realizing it, the electric companies and the K-6 science textbooks are trying to re-define the original meaning of the word electricity. How can such a thing happen? I'll examine this, but first here are more facts about "electricity" as scientists use the word.

MORE TRUE STATEMENTS ABOUT "ELECTRICITY"

In a DC circuit, the electricity within the wires flows exceedingly slowly; at speeds around inches per minute. At the same time, the electrical energy flows at nearly the speed of light.

If we know the precise amount of electricity flowing per second through a wire (the Amperes,) this tells us nothing about the amount of energy being delivered per second into a light bulb (the Watts.) Amperes are not Watts, an electric current is not a flow of energy; they are two different things.

In an electric circuit, the flow of the electricity is measured in Coulombs per second (Amperes.) The flow of energy is measured in Joules per second (Watts.) A Coulomb is not a Joule, and there is no way to convert from Coulombs of charge into Joules of energy, or from Amperes to Watts. A quantity of electricity is not a quantity of energy.

Electrical energy is electromagnetism; it is composed of an electromagnetic field. On the other hand, the particles of electricity (electrons) flowing within a wire have little resemblance to an electromagnetic field. They are matter. Electricity is not energy, instead it is a major component of everyday matter.

In an electric circuit containing coils, if we reverse the polarity of voltage while the direction of the flowing electricity remains the same, then the direction of the flowing energy will be reversed. Current same; energy flow reversed? Yes. A flow of energy does not follow the direction of the flowing electricity. You can know everything about the direction of the electricity within a wire, but this tells you nothing about the direction of the flowing electrical energy.

In any electric circuit, the smallest particle of electrical energy is NOT the electron. The smallest particle of energy is the "unit quantum" of electromagnetic energy: it is the photon. Electrons are not particles of EM energy, neither do they carry the energy as they travel in the circuit. Electricity is 'made' of electrons and protons, while electrical energy is electromagnetism and is 'made' of photons.

In the electric power grid, a certain amount of energy is lost because it flys off into space. This is well understood: electrical energy is electromagnetic waves travelling in the air, and unless the power lines are twisted or somehow shielded, they will act as 60Hz antennas. Waves of 60Hz electrical energy can spread outwards into space rather than following the wires. The power lines can even receive extra 60Hz energy from space, from magnetic storms in Earth's magnetosphere. Electric energy is gained and lost to empty space while the charges of electricity just sit inside the wires and wiggle. Energy is not electricity.

In an electric circuit, electrical energy does not flow inside the copper. Instead it flows in the empty air surrounding the wires. This fact is hidden because we calculate energy flow by multiplying voltage times current. College-level physics books describe a less misleading method of measuring this energy flow: take the vector cross-product of the E and M components of the electromagnetic field at all points in a plane penetrated by the wires. We call this the Poynting Vector field. Add these measurements together, and this tells us the total energy flow (the Joules of energy that flow each second through the plane.) In other words, in order to discover the rate of energy flow, don't look at the flowing electrons. The electricity flow tells us little. Instead look at the electromagnetic fields which surround the wires.

How can dictionaries, encyclopedias, and textbooks make such a gigantic error about electricity? I'm not certain, but I suspect that the mistake was missed because it slowly crept into the books over many decades. Most people practice "learning" rather than "unlearning." Since we accumulate knowledge rather than busting misconceptions, we never stumbled across the problem. Since most people don't really understand electrical physics, nobody complained, or even noticed. And if you raise the temperature of the lobster pot slowly enough, the live lobsters won't realize that they're in trouble! (grin)
What about the experts? Why don't the science experts complain? Here's one reason: modern scientists used the term "electricity" less and less over the years. Perhaps they're aware of the creeping distortion of the word "electricity", and so they avoid using it. Instead they adopted some improved terminology. Scientists of today don't say "charges of electricity" anymore. Instead they call it "electric charge." Also, modern scientists no longer say that electric current is "a flow of electricity." Instead they call it "a flow of charge." They also say that electrons are "charge carriers" rather than "particles of electricity." Even Faraday's Law has been changed, and today scientists usually speak of "quantities of charge" rather than the "quantities of electricity" discussed in the traditional definition of the Electrolysis Law.
If today's scientists notice their textbooks asserting that "electricity is energy", they will not necessarily realize that this is an error. They will not realize that the phrase "electricity is energy" makes the same mistake as this erroneous statment: "electric charge is a type of energy." Scientists no longer use word "electricity" in their day-to-day science profession, they mostly use it when explaining physics to children. As a result, they don't rigorously police their own usage of the word "electricity" in uncritical situations, and they don't notice when children's textbooks get it wrong.
Also, contemporary scientists are in the same position as everyone else: they learned some of their terminology in elementary school, and if their books were wrong, their minds might still retain those errors. If every one of us learns in grade school that the charges of "electricity" are a form of energy, we may remain blind to the contradictions even when we grow up to become scientists. The scientists put the mistakes in a mental pigeonhole and never use them during work, but they still may bring them out when explaining electricity to non-experts. I caught myself doing this at the start. I doubt I'm the only one with this problem.
Another reason why the error was never fixed: if an error becomes extremely widespread, and hundreds of thousands of people begin making the same mistake, then the error will become invisible. Those people will refuse to even acknowledge the error as being an error. After all, this many people cannot be wrong! Oh yeah? The majority rules? Not where the real world is concerned! It doesn't matter how many people make a factual error: the error remains just as wrong. However, any expert who objects, and who tries to fix the massive error, they will perhaps be seen as grammar-nitpickers living in ivory towers. The ones who have the ambition to point out the error are easily ignored because they are so few.
In most school subjects, majority does rule, and the "grammar nitpickers" are actually wrong. For example, if millions of people use slang words in their daily speech, then eventually those slang words will become acceptable. The words themselves didn't change ...yet they're no longer slang. As the slang is used over many years, dictionaries eventually include those words (dictionaries RECORD definitions, they don't promote them, and the common mistakes are recorded too.) Eventually all the dictionaries will include the slang words, and those words will become proper English and will be slang no longer. For this reason, people usually ignore Grammarians who object to the "misuse" or "corruption" of the English language. Such misuse is a matter of opinion.
But Science classes are different than English classes. In Science, reality rules, and if a large group of non-scientists tries to change the description of the real world, then that large group falls into error. It doesn't matter how many people "vote" for the change, because Nature isn't listening. If "electricity" originally means electric charge, and if people try to change things so that the word "electricity" now means energy, then we have a special word for their actions: MISTAKEN TERMINOLOGY.
I don't quite know how to solve the problem regarding the word "electricity." Too many reference books contain the errors. The word has been misused for so many decades that I am tempted to follow the lead of the scientists: just give up! Just admit that the word Electricity is irretrievably contaminated, and simply abandon it. Abandon it silently, that way nobody has to get embarrased. Yet doing this silently has caused serious problems in the past. It doesn't fix the problem, it just covers it up.
Abandoning the word electricity might defend Science against the brain-damage caused by contradictory terminology, but it does nothing to fix all of the reference books which are filled with confusing explanations of "electricity." More importantly, if we quietly abandon the word "electricity" without discussion, this will do nothing to help all of the poor souls who are currently confused by the incorrect "electricity" concepts. Neither will it give any aid to all of the poor science students who are butting their heads against the contradictory material still present in their science textbooks.

William Beaty 1999 souce : http://amasci.com

DANGERS OF ELECTRICITY

2012-09-09T12:39:00.001-07:00

DANGERS OF ELECTRICITY

Staying safe around electricity is everyone's responsibility.
You should watch out for yourself, your friends and your family.

Electricity is part of our everyday life - designed to provide us with a safe and reliable source of energy. Most of the time, electricity is our friend, but sometimes it can be dangerous. This happens when we're exposed to it in ways we were not meant to be. We can avoid these hazards by following some simple rules.

Electricity and water do not mix

Remember
If your hands tingle when you put them into the sink it may mean the water is conducting electricity and something is wrong. Let Mum or Dad know, as they may need to call an electrician.

When you have a bath, there should be nothing electrical anywhere near you. In a bath, the metal plughole and the plumbing is connected to the earth, making it a conductor of electricity. This means if a household appliance such as a light or hair dryer fell into the bath, whoever was in it would also become a conductor of electricity.

Wherever you are, if you get into trouble call out for help and make sure not to touch anything. Get whoever helps you to turn the electricity off.

Water can conduct electricity because electrons can flow by hitching a ride on atoms and molecules in the water. Water contains dissolved substances, such as salt. These greatly increase the ability of water to conduct electricity. That's why electricity passes easily through our bodies - because our bodies contain water and salt. This is also why it's important to keep water away from electrical appliances.

Be careful around electricity poles and wires when you play

Remember
If you fly a kite and it gets caught in the overhead powerlines, live electricity could travel down the string and seriously hurt you. So be careful!

Never climb a tree that is near powerlines. Look up before you climb!

After a storm if you see some fallen powerlines, stay well clear of them.
There is a strong chance they are still "alive".

We all like to play outside, but there are electrical hazards that we need to know about. Electricity poles and wires are all around us. They can be above us, next to us, and even below us. Whenever you can, play in open spaces away from electricity poles, towers and powerlines.

Metal is a conductor of electricity and can be dangerous

Remember
Never put a metal object - like a knife - into a toaster. It is very dangerous!

Never put anything in a power point that's not meant for it. Electricity will travel right up the metal object into your body.

Be careful when climbing a ladder at home. The power lines connected to our house are usually protected, but they can be damaged by rubbing against the gutter or a tree, or through exposure to the sun.

If a person is on a metal ladder and touches the exposed line, the electricity will travel through their body to the earth.

We all come into contact with metal objects on a daily basis - turning on a tap, playing with our computers and toys and even using the fridge. Because metal conducts electricity, you have to be very careful when you use metal items.

Stay away from electricity substations

Remember
Sometimes it's tempting to ignore signs and fences around substations. Remember, the warnings are there for everyone's protection, so make sure you follow them!

Substations contain special equipment with invisible hazards. You don't even have to touch anything to get hurt.

Just being too close to some substation equipment can be dangerous, and may even kill you!

You will find electricity substations and power equipment all over the place. They are behind fences, in buildings, or on the side of the footpath, and most have danger signs. Substations transform the voltage generated at power stations so it can be distributed to homes, schools and businesses. Sometimes they are near parks and play areas. Substations are safe, but you must follow the rules.

If you see a dangerous situation involving electricity, tell an adult!

Remember
Faulty appliances and damaged electrical leads should be disconnected at the power point and fixed or replaced by an electrician.

Never stack power points. Use a power board or have an extra power point installed. Stacked power points can cause fires.

Always be on the look out for dangers in and around your home. This could be anything from a faulty electrical lead to a "stacked" power point - one with too many plugs in it. These situations could be life threatening and an electrician should be called in to fix them.

Know what to do in an electrical emergency

If you come across an emergency involving electricity
Ensure your own safety

Turn the power off at the power point and remove the plug (if you are able to do so)

Get an adult

Ring 000

We all hope that we are never in an emergency involving electricity, but if we are, it's important to know what to do.

DIAL BEFORE YOU DIG!

Remember
Before you or your family do any major digging in the yard you should get Mum or Dad to ring Dial Before you Dig on 1100 to make sure there are no underground cables near your property.

If you hit a buried power line you could be electrocuted, as well as possibly interrupting the power to your suburb.

2012-09-09T06:31:00.003-07:00

Voltage

Why Do You Need To Know About Voltage?

Voltage

Measuring Voltage

Problems

You are at: Basic Concepts - Quantities - Voltage
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Voltage We usually try to start each lesson by giving reasons why you want to learn the lesson topic. However, if you have ever had the misfortune of grabbing a live wire with more than a few volts you might already have the answer to why you want to learn about voltage. You've probably seen the signs that say "Danger High Voltage", and you've probably talked about things or people being "High Voltage". A high voltage individual is one with a lot of energy and drive. That's apropos.
Still voltage is important - and not just to electrical engineers - because it is the medium used to transmit information and energy in our world.

Goals Here are the objectives for this lesson.

Given an electrical circuit:

Be able to define voltages for elements within the circuit,
Be able to measure voltages for elements within the circuit.

What Is Voltage? - Ways Of Thinking About Voltage Voltage is a physical variable that can be thought of in different ways. Here are a few ways you can think about voltage.

Voltage can be thought of as the driving force (although it is not really a "force".) behind current. Things like batteries are voltage sources. The voltage across the terminals of a battery tends to stay pretty constant. When you connect a device across the battery terminals a current flows through the device.
Current flows through electrical elements when a voltage appears across the terminals of the element, just like water flows through a pipe when a pressure difference appears across the pipe. You can use that analogy to get started thinking about voltage.

More ways of thinking about voltage are:

Voltage is an across variable (Whereas current is a through variable, remember?). Water pressure that causes water flow is also an across variable. We talk about pressure differences and voltage differences.
Voltage is a concept that is related to potential energy. Voltage is the electrical potential energy a charge has by virtue of its position in space. Where the charge is affects the energy it has because other charges exert forces on it. When forces are exerted on the charge, then it may require energy to move the charge between two points, or, conversely, the system may release energy as the charge moves between two points.

Because there are electrical forces there are concepts like potential energy that can be used in electrical systems. What's more, the electrical forces obey an inverse square law, just like gravitational forces, so a lot of concepts carry over. Those gravitational force field concepts are important. Electrical fields have much in common with gravitational fields, and a number of those concepts carry over to electrical fields. The electrical force law and the gravitational are both inverse square laws. Because the fundamental force law is the same, many of the concepts developed for gravitational forces can be taken over to electrical concepts because the underlying mathematics is the same. Those electrical concepts will be almost exactly the same except that charge will play the role in electrical forces that mass plays in gravitational forces. Here are some of the important ideas that carry over.

Potential energy that is a function only of position is a direct result of the inverse square force law. Both gravitational masses and electrical charges obey an inverse square law.
Potential energy can be converted into other forms of energy. In a gravitational field, masses can fall together (due to mutual attraction) and the potential energy can be converted to heat and kinetic energy.
A mass can acquire kinetic energy in an gravitational field and later that kinetic energy could be converted to heat. Charges attached to masses can acquire energy in an eletrical field, and that kinetic energy can be converted to heat.

The many concepts that carry over from gravitational systems help to make voltage a much richer concept. Think of some of the implications.

If you pull two masses apart (by lifting a weight to a higher position on the earth, for example) you put potential energy into the system. If you pull two attracting charges apart you put potential energy into the system.
That potential energy can be converted into other forms of energy. If you have a charge with potential energy, you can generate light, heat, mechanical motion and you can even store chemical energy.

Voltage Concepts In electrical fields, we will want to think in terms of the potential energy per unit of charge. Near the earth's surface the potential energy of a mass, m, h meters above the surface is mgh. The potential energy per unit mass is just gh. Voltage is the potential energy per unit charge for a charge in an electrical force field.
There are consequences of the inverse square law for electrical forces. Generally, those consequences are similar to what happens in gravitational systems.

In an electrical field, or in any conservative field like a gravitational field, we will have to do the same amount of work to move the charge between any two points A and B, no matter what path we take in moving the charge. Work done in a conservative field is said to be "path independent".
The potential energy in a gravitational field and the voltage in an electrical field (potential energy per unit of charge) are functions of position only.

One important consequence is a relationship between energy put into a charge as it moves.

If we move a charge from point A to point B, and put a given number of joules of work into the charge, we will recover exactly the same number of joules from the charge if it moves back from point B to point A. If we move the charge through any closed path or circuit, there will be no net energy input to the system and no net energy recovered from the charge.
If we move a charge from point A to point B, the number of joules of work we put into the charge can be calculated by multiplying the charge, Q, by the voltage difference between points A and B, V_ab.

ProblemP1 What are the units of voltage in the MKS system? Remember, that voltage
is potential energy per unit of charge.

We can draw a number of analogies between voltage and gravitational potential energy. Consider the circuit below. The element shown in yellow "pumps" charge from a lower potential - the bottom terminal of the yellow element, to a higher voltage (potential energy per unit charge, remember?) at the top of the yellow element. That's like lifting a weight from a low position (a position with lower potential energy) to a higher position (one with more potential energy). Click to button to see what happens as the charge moves around the circuit.

        There's a point to the simulation above. A battery, or any other voltage source, is a sort of charge pump. If you buy a battery and you connect something to it, it will supply charge at some specified voltage to your applied electrical load. If the charge is pumped up to nine (9) or twelve (12) volts, for example, then when you connect a load to your battery charge will flow out of your battery, through the load. Energy will be transferred to your applied load from the battery.        What happens in this situation with regard to the energy involved? When the charge goes through the battery, and is "pumped" up to, say, twelve (12) volts it acquires potential energy. As it flows through the load it gives up this potential energy to the load. If the load is a motor that energy might be transformed into mechanical energy, potential (by lifting a weight) or kinetic (by turning a flywheel). If the load is a light bulb, the energy is transformed into light and heat.
        Here's a simple circuit. A battery (remember the special symbol for a battery) is connected to two elements in series. Charge/current flows out of the battery, through element "1", out of element "1", into element "2" and out of element "2" back into the battery. As the charge flows through the battery it acquires energy. Some of that energy is given up to element 1, then some of that energy is given up to element 2. Note that:
Energy Gained in the battery = Energy lost in Element "1" + Energy lost in Element "2".        Note that this is simply a statement of Conservation of Energy.
        Now, if we know the voltages at points in the circuit, we can compute the work done as the charge moves (current flows) around the circuit. Let's imagine that we have two (2) couloumbs of charge and we move it around the circuit shown above. Let's compute how much work will be done as the charge moves through the circuit. We will pose that as a sequence of short problems.

What points should you remember from this? If you can put potential energy into a charge (as in a battery, for example) then whatever energy the charge acquires in the process is transferred totally to whatever elements the charge passes through as it wends its way back to the point where it has no potential energy. Electrical engineers would say this slightly differently. Here's how they would say it.

If a charge is raised from zero voltage (zero potential energy) to a higher voltage (as in a battery, for example), then when that charge moves back to the point of zero potential energy it passes through voltages that sum to whatever the voltage was that it passed through to acquire the energy.

This is really a statement of conservation of energy, and you can realize that once you remember that voltage is really potential energy per unit of charge. We also need to be more precise in our discussion of voltage. Engineers communicate with symbols, and they use special symbols to show voltages. Let's look at the circuit we used earlier.

We have added symbols to define all of the voltages in the circuit. For example, we have defined a symbol, V_B, that represents the voltage across the battery. For the voltage, V_B , as we have defined it, we can compute the energy added to a charge, Q, when it moves from the bottom of the battery (at the "-" sign) to the top of the battery (at the "+" sign) as Q*V_B. Let's get a complete set of statements about what happens as charge moves around this circuit.

As a charge, Q, moves from the bottom of the battery (at the "-" sign) to the top of the battery (at the "+" sign), the charge gains an amount of energy, Q*V_B. The units are coulombs for charge, volts for voltage and joules for energy.
As a charge, Q, moves from the top of element #1 (at the "+" sign) to the bottom of element #1 (at the "-" sign), the charge loses an amount of energy, Q*V₁.
As a charge, Q, moves from the top of element #2 (at the "+" sign) to the bottom of element #2 (at the "-" sign), the charge loses an amount of energy, Q*V₂.

We can generalize these statements.

If we have used the convention introduced above - with "+" and "-" signs - for voltage, then when a charge, Q, moves from the end of the element labelled with a "-" sign to the end of the element labelled with a "+" sign, the charge gains QV joules, where V is the voltage across the element.

Measuring Voltage        If you deal with circuits you will need to be able to measure voltages in circuits. That's the one skill you absolutely must have if you want to check that a circuit is operating properly. You know that Murphy's law prevails. If anything can go wrong, it will.
        You will always need to check a circuit's operation to see if it is working correctly. Actually, you'll probably need to check it to find out why it isn't working. Many times you will do that using a voltmeter. In this section we'll discuss how to use a voltmeter to measure voltages in an operating circuit. (Click here for a longer discussion of measuring voltage, and links to some experiments.)
        There are many other situations in which you would want to be able to measure voltage. For example, you might have an LM35 temperature sensor. Then the output of the sensor is a voltage that is proportional to the temperature of the sensor.
        We will give you a choice here. You can continue in this lesson, or you can read the lesson devoted entirely to voltage measurements. Click here to go to that lesson which covers numerous laboratory measurements and gives you several experiments to perform.
Using a Voltmeter
        Here's a representation of a voltmeter. For our introduction to the voltmeter, we need to be aware of three items on the voltmeter.

The display. This is where the result of the measurement is displayed. Your meter might be either analog or digital. If it's analog you need to read a reading off a scale. If it's digital, it will usually have an LED or LCD display panel where you can see what the voltage measurement is.
The positive input terminal, and it's almost always red.
The negative input terminal, and it's almost always black.

Next, you need to be aware of what the voltmeter measures. Here it is in a nutshell.

A voltmeter measures the voltage difference between the positive input terminal of the voltmeter and the negative input terminal.

That's it. That's what it measures. Nothing more, nothing less - just that voltage difference. That means you can measure voltage differences in a circuit by connecting the positive input terminal and the negative input terminal to locations in a circuit.

Next, we'll look at a circuit diagram. We'll show a voltmeter connected to the circuit diagram - a mixed metaphor approach. Forgive us for that, but let's look at it. It's right below.
Here's a voltmeter shown connected to a circuit. This shows where you would place the leads if you wanted to measure the voltage across element #4.

Notice that the voltmeter measures the voltage across element #4, +V₄.
Notice the polarity definitions for V₄, and notice how the red terminal is connected to the "+" end of element #4. If you reversed the leads, you would be measuring -V₄.

Here's a portion of a circuit board. You want to measure the voltage across R27. Click on where you should put the voltmeter leads.

What If ? At this point, you're starting to become comfortable with voltage. Don't become too comfortable. Always respect two things about voltage.

It can give you a shock, and a large enough voltage can be lethal.
It's more complicated than we've really indicated so far.

You Need To Know More About Voltage So far, we've just examined voltage as though it were across one device. However, if we look at the example circuit we used before we realize that there are lots of voltages in this circuit. If we measure them, how do we know our measurements make sense? There are laws that voltage obeys. The most important one is Kirchhoff's Voltage Law (click here to go to the lesson!), (KVL) and it's the subject of another lesson. It is an important relationship that voltage obeys, and it is the starting point for analysis of circuits of any complexity. That's it for this lesson. You can exit this lesson and start another lesson by clicking the up-pointing arrow below. Or you can go directly to several places from this page. You can use any of these hotwordsto take you to a lesson of your choice.

Kirchhoff's Voltage Law.
Current
Resistors - which are devices that have a specific relation between the voltage across them and the current through them.

2012-09-09T06:29:00.002-07:00

A Short Note About Circuit Diagrams & Symbols
                You probably already know that electrical engineers do not draw pictorial diagrams for every circuit. Instead, they draw symbolic diagrams that represent a physical situation. Do you remember this circuit?

Now, imagine that the element shown as a yellow rectangle is a battery. We would draw this circuit as shown at the right. Notice the symbol for the battery, with the "+" and "-" signs. Notice also the two elements, shown here as rectangles. Later, we will examine some symbols for particular elements.
        These diagrams may not look like the physical system, but they form a sort of language that allows precise communication between engineers about exactly what comprises a particular circuit. Different kinds of electrical elements have different symbols. Sometimes new symbols have to be invented when someone invents a new electrical device.
        Here are some symbols that are used for some common components.

electricity basic concept

2012-09-09T06:28:00.000-07:00

Why Do You Need To Know About Electrical Energy?
A power station is a place where other forms of energy - coal, gas, potential energy in water and nuclear energy - are turned into electrical energy for transmission to places that use electrical energy. Electrical engineering is concerned with transmission and ultilization of two things - energy and information. Here, in this lesson, we are going to focus on power and energy. In this lesson you will want to learn the following.

   Given an electrical circuit or device

   Be able to compute instantaneous rate of energy use (power).
   Be able to compute how much energy is used over a period of time.
   Be able to compute how much energy is stored in an electrical storage device like a battery or a capacitor.

What Is Electrical Power?

Electrical power is conceptually simple. Consider a device that has a voltage across it and a current flowing through it. That situation is shown in the diagram at the right.

The voltage across the device is a measure of the energy - in joules - that a unit charge - one couloumb - will dissipate when it flows through the device. (Click here to go to the lesson on voltage if you want to review.) If the device is a resistor, then the energy will appear as heat energy in the resistor. If the device is a battery, then the energy will be stored in the battery.
The current is the number of couloumbs that flows through the device in one second.j (Click here to go to the lesson on current if you want to review.)
If each couloumb dissipates V joules, and I couloumbs flows in one second, then the rate of energy dissipation is the product, VI.

That's what power is - the rate at which energy is expended. The rest of the story includes these points.

It doesn't matter what the electrical device is, the rate at which energy is delivered to the device is VI as long as the voltage and current are defined as shown.
The power can be negative. If the device is a battery, then current - as defined in the figure - can easily be negative if, for example, a resistor is attached to the battery. If the power is negative, then the rate at which the device expends energy is negative. That really means that it is delivering energy in that situation.

Power in Electrical Devices A resistor is one device for which you can compute power dissipation.

A symbol for a resistor is shown below, along with a voltage, V_r, across the resistor and a current, I_r, flowing through the resistor.

We can compute the power delivered to the resistor. It's just the product of the voltage across the resistor and the current through the resistor, V_rI_r.

But there's more to the story.

In a resistor, there is a relationship between the voltage and the current, and we can use that knowledge to get a different expression - one that will give more insight.
We know that V_r = Ri_r, so the power is just:

Power into the resistor = V_rI_r = (RI_r)I_r = R(I_r)².

We can also use the expression for the current I_r = V_r/R,

Power into the resistor = V_rI_r = V_r(V_r/R) = (V_r)²/R.

At different times, these two results - which are equivalent - can be used - whichever is appropriate. Besides being a useful result tthese are also illuminating results (And that's not a reference to the fact that a typical light bulb is a resistor that dissipates power/energy.).

The power dissipated by a resistor is always positive. That means that it does not (and in fact it could not) generate energy. It always dissipates energy - uses it up - contributing to the heat death of the universe.
We know the power is positive because R is always positive (and it will always be for any resistor that doesn't have hidden transistors) and because the square of the current has to be a positive number.

ProblemsP1. You have a 1KW resistor, and there is 25 volts across the resistor. Determine the power (in watts) that the resistor dissipates.

P2. You have a 25 watt light bulb that operates with 12.6 volts across it. Determine the resistance of the light bulb.

Power In Batteries       Batteries are ubiquitous components. They are in TV remotes, cell phones and things like that. But, batteries also appear in places you don't expect them to be. For example, you can turn this computer off. When you turn it back on it remembers things and recalculates things like the time. Now, you expect that for things that can be stored on a hard drive. You don't expect it for the time.
         When you turn this computer off and later turn it back on it will have the right date and time. How does it do that? If you think about it (and don't do that for too long!) you have to believe that there is a battery somewhere inside the computer and that when you turn the computer off that battery runs some sort of little clock hidden inside the computer. You can't see the clock and you wouldn't even know it's there, but you can probably see the time now on the task bar of this computer - and it's probably close to being right!
        Batteries are used to solve many problems.

They are used to provide power to run things like computer clocks that need to keep running even in the absence of AC power.
They are used to store energy for things like starting a car. When you run the car you generate energy (from the gasoline) and store it in the car battery. Then there is energy there when you need it to get the car going again.
They are used for low power devices to make them portable. That includes things like cell phones, TV remotes and calculators.

You use batteries - whether you want to or not, and whether you know it or not! You need to be able to compute some of the quantities involved. Here is a simple circuit where a resistor is connected to a battery. We know some salient facts about this circuit.

There is energy stored in the battery and the battery delivers stored energy to the resistor.
The resistor dissipates energy, and what happens physically is that the electrical energy that is delivered to the resistor gets turned into heat energy and the resistor becomes warmer.

Now, we need to look at a circuit diagram for this situation. That circuit diagram is shown to the right of the picture below.

In the diagram, we have defined a battery voltage, V_b, and a current, I_r.
Notice that we have used a natural definition for the current polarity. We have the arrow pointing out of the battery and into the resistor. We do that because we know that positive charge actually flows from the battery terminal through the resistor.
That definition of current polarity raises questions about calculation of power to/from the battery. Let us consider the power flow into the battery.

Power flow into the battery or any other device - is the product, VI, when

V is the voltage across the device, and
I is the current flowing into the device.

Remember, for our polarity conventions here, the current arrow points into the terminal of the device that is labelled "+" for the voltage definition.

We have reproduced the diagram from above here to emphasize how the voltage and current polarities are defined. Notice that the current arrow in our earlier definition points toward the "+" sign on the device.
In the battery-resistor circuit below, the current arrow is directed out of the positive ("+") terminal of the battery. That means the power delivered to the battery must be computed by (note the minus sign!):
P = - VI What does this mean? Let's look at a numerical example. Let's assume the battery voltage is 12 volts and the resistor is 24 ohms. That means the current is 0.5 amps, i.e.:
I_r = 12v/24W = 0.5a In other words, the power flowing into the battery is:
P = - V_b I_r = - 12 * 0.5 = - 6w

The power flowing into the battery is negative!
The power flowing out of the battery is positive!
And, it makes sense because we know the battery supplies power.

How much energy is stored in a battery?

Batteries are often rated in ampere-hours (or milliampere-hours) and an ampere-hour is really a unit of charge.
As a battery is used it discharges - charge flows from the battery - but it tends to hold a constant voltage. This is different than the internal resistance of the battery. What we are saying here is that as time goes on - for the same current drawn from the battery - the voltage stays about the same. There may be a slight drop-off but it is not very large.
Thus, if we have a 12.6 v battery, it will have something close to 12.6v until it gets close to being discharged.
Let's say we have a 12.6v battery rated at 70 ampere-hours.
Assuming it can deliver 1 ampere for 70 hours, then it will be delivering
Power = 12.6v x 1.0 amp = 12.6 watts for 70 hours.
That works out to 12.6 x 70 = 882 watt hours or .882 kw-hr. - and remember you pay the
electric company by the kilowatt-hour!
In joules we have 882 w-hr x 3600sec/hr = 3,175,200 joules.

That might sound like a lot, but an interested student might want to compare that amount of energy with the energy stored in a gallon of gasoline.