electricity you light up my life! what is electricity? electricity is one of the two long-range...

ElectricityElectricity

You Light Up My Life!You Light Up My Life!

What is Electricity?What is Electricity?

Electricity is one of the two long-range fundamental forces of nature; the other one being gravity.

Gravitational force between two bodies is always attractive and depends on mass (in kg). Electric force can be both attractive and repulsive and depends on charge (in Coulombs). In both cases the force falls with the square of the distance apart.

There are two kinds of electric charge; positive and negative. Like charges repel and unlike charges attract.

Gravity is a very weak force; electric forces are trillions of times stronger; but most materials have the same number of positive and negative charges, which cancel out, and so do not have any electric activity.

Atomic TheoryAtomic Theory

All matter in the universe is made up of around 90 different elements; with Hydrogen (H) being the lightest (and most common) and Uranium (U) the heaviest (there are artificial elements, mostly above U in the periodic table).

Atomic TheoryAtomic Theory

If you keep subdividing an element down, you reach the smallest particle that has the chemical properties of the element. This particle is called an atom (greek átomos; meaning indivisible).

Atoms are incredibly small. For instance a you could fit around 70 million carbon atoms across one of your hairs (0.1mm). One atom weighs 0.000 000 000 000 000 000 000 02gm (or around 20 trillion trillion would weigh a gram)!

Atoms are smaller than the wavelength of light and so cannot be seen even with the most powerful optical microscope. However, they can be visualised by bombarding with electrons. The picture to the right shows an array of carbon atoms taken with a scanning tunnelling electron microscope.

Atomic StructureAtomic Structure

The big question of the late Victorian era was could an atom be made up of even smaller components?

In 1874, the Irish physicist Johnston Stoney at a British Association conference meeting in Belfast predicted that there was a basic particle of electric charge as a constituent of the atom. He called these electrons.

In 1897 JJ Thompson applied a high voltage across electrodes (the positive called the anode and the negative the cathode) in a vacuum tube generated cathode rays, which seemed consist of negatively charged corpuscles. These had the predicted unit of charge.

JJ Thompson and one of his cathode ray tubes


Further experiments by Earnest Rutherford at the University of Manchester showed that the atom comprised of a number of electrons together with the same number of positively charged protons. Each particle carried one of Stoney’s fundamental charge measured as 1.6 10-19 Coulombs. Rutherford predicted that there would also be neutral particles in the atom, and neutrons were discovered in 1932 by James Chadwick at Cambridge.

A proton weighs in at around 1.6 10-24 gm against the lightweight electron which is around 9 10-38 gm, or 1/1836 of a proton. A neutron is only slightly heavier than a proton.

Rutherford left and Chadwick on the right


JJ Thompson thought that the atom consisted of a mixture of electrons and protons all mixed together; the plum pudding model (the positive and negative charges holding everything together). Electrons moved in rings inside this blob.

In 1909 Rutherford and Geiger shot alpha particles (negative Helium nuclei) from radium (a radioactive element) at very thin gold foil. Most went right through but a very few bounced back. From this he deduced that the atom was mostly empty space.

If all the space was removed from the human population of 6 billion, then the solid remainder would be the size of an apple!

Atomic Structure: Bohr modelAtomic Structure: Bohr model

By 1913 Neils Bohr, a Danish physicist, developed a model of the atom, where the electrons rotated in rings at a great distance from the positive nucleus, giving an overall neutral atom

Only certain orbits were allowed (like harmonics in a vibrating violin string) and only a maximum number of electrons could populate each orbit (inner 2, next out 8 etc). These electrons were stable, that is they wouldn’t spiral into the positive nucleus.

Electrons absorbing energy can make a quantum leap to a higher orbit, and conversely moving down causes radiation of energy as discrete frequencies of electro-magnetic waves (light, X-rays etc).

Atomic Structure: Bohr modelAtomic Structure: Bohr model

It is electrons in the outer orbit that interact with other elements, and thus give chemical properties. Thus elements in the same column in the periodic table have similar (not identical) properties; e.g. Carbon, Germanium, Silicon all have four electrons in their outer orbit. This orbit can hold a maximum of eight, so tend to steal electrons from other atoms; e.g. a molecule of Carbon Dioxide CO2 shares two electrons with two oxygen atoms back and forth.

The Bohr model is far too simplistic, and by the 1920s quantum mechanics painted a much more complex and mystical picture of sub-atomic physics, but the Bohr model still explains most of the phenomena useful in engineering

The Discovery of ElectricityThe Discovery of Electricity

The ancient Greek mathematician Thales wrote in around 600bce that The ancient Greek mathematician Thales wrote in around 600bce that rubbing amber (fossilised tree resin) with fur etc could cause attraction rubbing amber (fossilised tree resin) with fur etc could cause attraction between the two or even cause a spark. The Greek for amber is electron.between the two or even cause a spark. The Greek for amber is electron.

Study of magnetism goes back to the observation that certain naturally occurring stones attract iron.

There is some evidence that electroplating was used in Mesopotamia There is some evidence that electroplating was used in Mesopotamia around 300bce (the Bagdad battery). around 300bce (the Bagdad battery).

Attracting feathers with amber

Two Thousand Years LaterTwo Thousand Years Later

Around 1600, William Gilbert, a physician who lived in London at the time of Queen Elizabeth I and Shakespeare, studied magnetic phenomena and demonstrated that the Earth itself was a huge magnet. (Magnetism is really due to moving charges.)

He also studied the attraction produced when materials were rubbed, and named it the "electric" attraction. This is static electricity, usually caused when some electrons are rubbed off a material into another. In the picture below the little girl’s hair has been charged up and the hairs repel.

Benjamin FranklinBenjamin Franklin

In 1752, Franklin proved that lightning and the spark from amber were one and the same thing. This story is a familiar one, in which Franklin fastened an iron spike to a silken kite, which he flew during a thunderstorm, while holding the end of the kite string by an iron key.

When lightening flashed, a tiny spark jumped from the key to his wrist. The experiment proved Franklin's theory, but was extremely dangerous - he could easily have been killed.

Franklin coined the terms positive and negative charge, battery and conductor; still used today.

Galvani and VoltaGalvani and Volta

In 1786, Luigi Galvani, an Italian professor of medicine, found that when the leg of a dead frog was touched by a metal knife, the leg twitched violently. Galvani thought that the muscles of the frog must contain electricity.

By 1792, another Italian scientist, Alessandro Volta, disagreed: he realized that the main factors in Galvani's discovery were the two different metals - the steel knife and the tin plate - upon which the frog was lying. Volta showed that when moisture comes between two different metals, electricity is created. This led him to invent the first electric battery, the voltaic pile, which he made from thin sheets of copper and zinc separated by moist pasteboard.

Volta…continuedVolta…continued

In this way, a new kind of electricity was discovered, electricity that flowed steadily like a current of water instead of discharging itself in a single spark or shock. Volta showed that electricity could be made to travel from one place to another by wire, thereby making an important contribution to the science of electricity. The unit of electrical potential, the Volt, is named after him.

Alessandro Volta and one of his piles (batteries)

Andre Marie AmpereAndre Marie Ampere

Andre Marie Ampére, 1775 – 1836, a French mathematician who devoted himself to the study of electricity and magnetism, was the first to explain the electro-dynamic theory. A permanent memorial to Ampere is the use of his name for the unit of electric current.

http://www.corrosion-doctors.org/Biographies/AmperBio.htm

OhmOhm

Georg Simon Ohm, a German mathematician and physicist, was a college teacher in Cologne when in 1827 he published, "The Galvanic Circuit Investigated Mathematically". His theories were coldly received by German scientists, but his research was recognized in Britain and he was awarded the Copley Medal in 1841. His name has been given to the unit of electrical resistance.http://www.corrosion-doctors.org/Biographies/OhmBio.htm

Voltage = Current x ResistanceV = IR

Michael FaradayMichael Faraday

The credit for generating electric current on a practical scale goes to the famous English scientist, Michael Faraday (the unofficial patron saint of Electrical engineering). Faraday was greatly interested in the invention of the electromagnet, but his brilliant mind took earlier experiments still further. If electricity could produce magnetism, why couldn't magnetism produce electricity?

Faraday….continuedFaraday….continued

In 1831, Faraday found the solution. Electricity could be produced through magnetism by motion. He discovered that when a magnet was moved inside a coil of copper wire, a tiny electric current flows through the wire. Of course, by today's standards, Faraday's electric generator was crude (and provided only a small electric current), but he had discovered the first method of generating electricity by means of motion in a magnetic field.

Faraday …. continued

Faraday also realized that magnetic and electric forces acting at a

distance can be conceptualized as a force field; hence electric and

magnetic fields.

Left: Magnetic field from a bar magnet visualized using iron filings (miniature magnets lining up in the force field).

Right: Electric field showing direction of force (on a +ve charge) near a negative charge –q.

Edison and SwanEdison and Swan

Nearly 40 years went by before a really practical DC (Direct Current) generator was built by inventor Thomas Edison.

In 1878 Joseph Swan, a British chemist/electrician, invented the incandescent filament lamp and within twelve months Edison made a similar discovery in America.

“The aggregate capital now actually invested in electrical industries, principally electric lighting, (electric) railway and power distribution, is estimated by the same authority, as not less than $275,000,000”. Quote from the National Electric Light Association in 1889! www.edisonian.com/p004b002.htm

Edison and Swan…continuedEdison and Swan…continued

Swan and Edison later set up a joint company to produce the first practical filament lamp. Prior to this, electric lighting had been very powerful (too powerful for households) but crude arc lamps.

Edison used his DC generator to provide electricity to light his laboratory and later to illuminate the first New York street to be lit by electric lamps, in September 1882. Edison's successes were not without controversy, however - although he was convinced of the merits of DC for generating electricity, other scientists in Europe and America recognized that DC brought major disadvantages.

Left: A lamp used at the historic 1879 New Year’s Eve demonstration of the Edison Lighting System

in Menlo Park, New Jersey.

Nichola TeslaNichola Tesla

Power is the product of voltage and current (V I). High voltages in the home are dangerous! Thus Edison had to generate and distribute his dc power at lowish voltages (110V), but the cables had to carry large currents. Losses in the cables are proportional to current squared (I2R), but the problem with dc is that it is very difficult to change the voltage. With ac it is easy; just use a transformer. However, motors at the time would only run on dc.

Nichola Tesla, a Croatian engineer working for Edison, conceived the idea of 2- and 3-phase generation (in a dream) and on this basis patented a motor running alternating current. This removed the chief objection to ac, but Edison fought this tooth and nail. With Westinghouse, Tesla was instrumental in the design and implementation of the Niagara Falls hydroelectric scheme, which supplied New York, over 20 miles away, with electricity. This effectively won the battle of the currents.

Nichola Tesla continued…Nichola Tesla continued…

Left: Tesla monument at Niagra Falls (Canadian side), Queen Victoria Park, unveiled on July 9, 2006. Tesla is standing atop an AC motor.

Right: Tesla took out over 700 patents!

http://www.teslasociety.com/

The Information RevolutionThe Information Revolution

The use of electricity is critically important in The use of electricity is critically important in lighting, heating, and in mechanical lighting, heating, and in mechanical actuators/motors. actuators/motors.

Equally important is the use of electrons to Equally important is the use of electrons to generate, transmit, store and reproduce generate, transmit, store and reproduce information.information.

Information is a measure of change and Information is a measure of change and predictability. Conpredictability. Consider the two statements:sider the two statements:

1.1. Tomorrow the sun will rise and darkness will Tomorrow the sun will rise and darkness will be banished.be banished.

2.2. Tomorrow an extinct volcano will erupt in Tomorrow an extinct volcano will erupt in Belfast. Belfast.

Which one carries the most informationWhich one carries the most information?? Because electrons are so light, changes Because electrons are so light, changes ((called called

signalssignals) can be sent along a conductor or ) can be sent along a conductor or propagated in space uspropagated in space using radio or light waves ing radio or light waves at at speeds approaching that of light.speeds approaching that of light.


Up to the early 1800s the fastest you could send Up to the early 1800s the fastest you could send information was on horse by land or sailing ship information was on horse by land or sailing ship by sea. A horseman carrying a message had to by sea. A horseman carrying a message had to transport around 500kg of animal over rocks, transport around 500kg of animal over rocks, muddy ruts and fallen trees with plenty of food muddy ruts and fallen trees with plenty of food for the two mammals.for the two mammals.

With a reliable source of electricity, around 1830 With a reliable source of electricity, around 1830 many experiments were made in sending many experiments were made in sending currents along wires to deflect a needle at the far currents along wires to deflect a needle at the far end (magnetic field). end (magnetic field).

Wires were strung on poles along railway lines to Wires were strung on poles along railway lines to signal oncoming trains and synchronise time signal oncoming trains and synchronise time (railway time). In UK by 1838 there was 20km (12 (railway time). In UK by 1838 there was 20km (12 miles) of line, by 1852 there were 6,000km (4,000 miles) of line, by 1852 there were 6,000km (4,000 miles).miles).

The British system (Wheatstone & Cook) used The British system (Wheatstone & Cook) used multiple wires and five needles to point to each multiple wires and five needles to point to each letter in turn!letter in turn!


Reducing the number of wires and reliability of the telegraph was a Reducing the number of wires and reliability of the telegraph was a priority, and the number of needles was steadily reduced and priority, and the number of needles was steadily reduced and various codes were used to encode alphanumerics.various codes were used to encode alphanumerics.

Samuel Morse (portrait Painter) with Alfred Vail came up with a code, Samuel Morse (portrait Painter) with Alfred Vail came up with a code, which relied on each letter being coded by a series of dots and which relied on each letter being coded by a series of dots and dashes. The more common letters had a shorter code:dashes. The more common letters had a shorter code:. .-.. . -.-. - .-. .. -.-. .. - -.-- . .-.. . -.-. - .-. .. -.-. .. - -.-- E l e c t r i c i t yE l e c t r i c i t yThese current pulses could be used to close a relay switch and thus These current pulses could be used to close a relay switch and thus regenerate the signal along the link, and at the receiver mark a paper regenerate the signal along the link, and at the receiver mark a paper tape or actuate a buzzer.tape or actuate a buzzer.

In 1844 first government-funded demonstration between Baltimore In 1844 first government-funded demonstration between Baltimore and Washington (37 miles). Message sent “What has God and Washington (37 miles). Message sent “What has God wrought?”wrought?”


“It is difficult to imagine how strange the telegraph must have seemed to our great, great grandparents. People had only the vaguest idea about the technology involved.

One railway passenger who left her umbrella on the train asked at the station if it could be found. The stationmaster said he'd try to use the telegraph to arrange for its return and wired to the end of the line to see if it had been found on the train. Soon, he received a message back that it had and would be sent back 'down the line'. When he told the anxious passenger this good news, she expressed amazement that items such as umbrellas could be returned using the telegraph!

Rather than disappoint her, the station staff hooked the returned umbrella over the telegraph wire - as if it had literally come back 'down the line'.”

http://www.connected-earth.com/Galleries/index.htm


Key to building an international communications Key to building an international communications web was undersea cables; first across rivers and web was undersea cables; first across rivers and then seas.then seas.

Needs great strength and good insulation; Needs great strength and good insulation; invention of gutta-percha (rubber) led in 1850 to invention of gutta-percha (rubber) led in 1850 to first international submarine telegraph between first international submarine telegraph between Dover and Cap Gris Nez (France). Four private Dover and Cap Gris Nez (France). Four private investors each put up £500. Failed after a few investors each put up £500. Failed after a few messages! messages!

The wonder of the Victorian age (equivalent to The wonder of the Victorian age (equivalent to putting a man on the moon) was the transatlantic putting a man on the moon) was the transatlantic link. Can you think of any problems laying 1,852 link. Can you think of any problems laying 1,852 miles (2,980 km) of cable?miles (2,980 km) of cable?

In 1857 and 1858 the HMS Agamemnon and USS In 1857 and 1858 the HMS Agamemnon and USS Niagara met in mid-Atlantic, spliced the cable and Niagara met in mid-Atlantic, spliced the cable and sailed back towards their respective continents. sailed back towards their respective continents. Queen Victoria sent President Buchanan a 98-word Queen Victoria sent President Buchanan a 98-word message. Took 17 hours!message. Took 17 hours!

Authenticated left-over pieces of transatlantic cable sold


In an attempt to increase the signalling rate some In an attempt to increase the signalling rate some genius decided to use 2,000 volts and ……………genius decided to use 2,000 volts and ……………

It would take 12 years (and an American civil war) It would take 12 years (and an American civil war) and seven attempts before a working link was and seven attempts before a working link was established, with an investment of the equivalent established, with an investment of the equivalent of billions of pounds.of billions of pounds.

The final cable (all 5,000 tonnes) was laid by The final cable (all 5,000 tonnes) was laid by Brunel’s giant Great Eastern ship from Valentia Brunel’s giant Great Eastern ship from Valentia (Dingle Bay) to Heart’s Content in Newfoundland.(Dingle Bay) to Heart’s Content in Newfoundland.

Lord Kelvin had invented the mirror galvanometer Lord Kelvin had invented the mirror galvanometer (very sensitive) and this allows a transmission rate (very sensitive) and this allows a transmission rate of up to 20 words per minute with low voltages!.of up to 20 words per minute with low voltages!.

In 1871 a cable was laid to Australia via Singapore.In 1871 a cable was laid to Australia via Singapore. By 1902 with the completion of a line from British By 1902 with the completion of a line from British

Columbia to New Zealand, telegraph cables now Columbia to New Zealand, telegraph cables now circumnavigate the globe.circumnavigate the globe.

The first Telephone (speech) transatlantic cable The first Telephone (speech) transatlantic cable was not laid until 1956!was not laid until 1956!


1924


The electric telegraph was a digital communications The electric telegraph was a digital communications network; people speak in tones.network; people speak in tones.

To send sounds down a wire, you need to:To send sounds down a wire, you need to: Convert sounds to electric current vibrations (that Convert sounds to electric current vibrations (that

is an analogue to the original air pressure is an analogue to the original air pressure variations).variations).

Transmit these currents to the desired receiver.Transmit these currents to the desired receiver. Turn electrical current variations back to pressure Turn electrical current variations back to pressure

waves (sounds)waves (sounds) Many people working at transmitting tones down a Many people working at transmitting tones down a

telegraph wire around 1870s, in order to try and send telegraph wire around 1870s, in order to try and send more than one morse-code message at a time more than one morse-code message at a time ― ― multiplexingmultiplexing..

Also experiments in teaching deaf people to recognise Also experiments in teaching deaf people to recognise sounds with vibrating membranes.sounds with vibrating membranes.

Telephone-like instruments 1862 Telephone-like instruments 1862 1872, developed by 1872, developed by Philipp Reis; German physics instructor.Philipp Reis; German physics instructor.

http://atcaonline.com/phone/


The invention of the first practical telephone is normally attributed to The invention of the first practical telephone is normally attributed to Alexander Graham Bell, a Scottish scientist (with a deaf wife) who was Alexander Graham Bell, a Scottish scientist (with a deaf wife) who was working in Canada. Patented in 1876. Also Edison’s carbon microphone.working in Canada. Patented in 1876. Also Edison’s carbon microphone.

Lord Kelvin exhibited Bell's telephone to the British Association for the Lord Kelvin exhibited Bell's telephone to the British Association for the Advancement of Science at Glasgow in September. He described it as "the Advancement of Science at Glasgow in September. He described it as "the greatest by far of all the marvels of the electric telegraph". 1877greatest by far of all the marvels of the electric telegraph". 1877

Bell demo’ed to Queen Vic in 1878, with a long-distance call to Southampton. Bell demo’ed to Queen Vic in 1878, with a long-distance call to Southampton. What do you consider to be the major problem with distance connections? What do you consider to be the major problem with distance connections?

1879 first public telephone exchange: Eight subscribers.1879 first public telephone exchange: Eight subscribers. 1880 first London telephone directory in January covered three exchanges 1880 first London telephone directory in January covered three exchanges

and 250 subscribers. By April, 7 London exchanges, 16 provincial exchanges and 250 subscribers. By April, 7 London exchanges, 16 provincial exchanges and 350 subscribers …..and 350 subscribers …..

The first operators were boys, who turned out to be impatient and rude when The first operators were boys, who turned out to be impatient and rude when dealing with phone customers. Their rudeness made them extinct within only dealing with phone customers. Their rudeness made them extinct within only a few years, replaced by females who were, "calm and gracious”a few years, replaced by females who were, "calm and gracious”


Long-distance links require amplification: Long-distance links require amplification: active electronic devices.active electronic devices.

In 1904 Ambrose Fleming invents the thermonic In 1904 Ambrose Fleming invents the thermonic diode.diode.

Followed by Lee DeForest’s triode amplification Followed by Lee DeForest’s triode amplification valve (tube) in 1906. A small voltage on a grid valve (tube) in 1906. A small voltage on a grid could control a large current flowing between a could control a large current flowing between a hot cathode and anode.hot cathode and anode.

This led to the electronic revolution, with radio This led to the electronic revolution, with radio (wireless), telephone repeaters, audio (wireless), telephone repeaters, audio amplifiers and television etc.amplifiers and television etc.

Telephone exchanges were automated during Telephone exchanges were automated during the 20the 20thth century (In Donegal not until late 1980s) century (In Donegal not until late 1980s) and the switching technology formed the and the switching technology formed the technological basis for the comeback of digital technological basis for the comeback of digital networks, such as computers.networks, such as computers.


AlAlthough all the theory was known by the end though all the theory was known by the end of the 2of the 2ndnd World war it took the invention of the World war it took the invention of the transistor in 1948 by Bardeen, Brattain and transistor in 1948 by Bardeen, Brattain and Shockley at Bell Laboratories to make it all a Shockley at Bell Laboratories to make it all a practical reality. practical reality. Transistors control electrons Transistors control electrons travelling through a soltravelling through a solid, such as silicon. id, such as silicon. Such structures can be made down to a few Such structures can be made down to a few hundred atoms in size (which is where we came hundred atoms in size (which is where we came in), no vacuum, no hot filament. Small size in), no vacuum, no hot filament. Small size means high speed and low energy required to means high speed and low energy required to switch.switch.

Hundreds of millions of these tiny switches can Hundreds of millions of these tiny switches can be put on wafers of silicon to make up an be put on wafers of silicon to make up an integrated circuit. Imagine a Pentium with 50 integrated circuit. Imagine a Pentium with 50 million hot, fragile and limited-life thermionic million hot, fragile and limited-life thermionic tubes! tubes!

ElectromagnetismElectromagnetism

James Clerk Maxwell (1831 - 1879) James Clerk Maxwell (1831 - 1879) developed the laws of developed the laws of electromagnetism in the form we electromagnetism in the form we know them today: Maxwell’s know them today: Maxwell’s EquationsEquations

Maxwell’s Equations are to Maxwell’s Equations are to electromagnetism what Newton’s electromagnetism what Newton’s Laws are to gravityLaws are to gravity

Note: It was Maxwell who realized the light is electromagnetic in nature

What is “Electricity”?What is “Electricity”?

- "Electricity" means electric charge.Examples: CHARGES OF ELECTRICITY. COULOMBS OF ELECTRICITY.

- "Electricity" refers to the flowing motion of electric charge. Examples: CURRENT ELECTRICITY. AMPERES OF ELECTRICITY.

- "Electricity" means electrical energy. Examples: PRICE OF ELECTRICITY. KILOWATT-HOURS OF ELECTRICITY.

- "Electricity" refers to the amount of imbalance between quantities of electrons and protons. Example: STATIC ELECTRICITY.

- "Electricity" is a class of phenomena involving electric charges. Examples: BIOELECTRICITY, PIEZOELECTRICITY, TRIBOELECTRICITY, THERMOELECTRICITY, ATMOSPHERIC ELECTRICITY ...ETC.

Electricity?Electricity?

Electricity is all about electrons, which are the Electricity is all about electrons, which are the fundamental cause of electricityfundamental cause of electricity

Static Electricity - involves electrons that are moved Static Electricity - involves electrons that are moved from one place to another, usually by rubbing or from one place to another, usually by rubbing or brushingbrushing

Current Electricity - involves the flow of electrons in a Current Electricity - involves the flow of electrons in a conductorconductor

Electric ChargeElectric Charge

Two kinds: positive and negative (terms coined by Two kinds: positive and negative (terms coined by Benjamin Franklin)Benjamin Franklin)

When you rub a glass rod with silk, the charge that is When you rub a glass rod with silk, the charge that is left on the glass was called positive. If you rub a hard left on the glass was called positive. If you rub a hard rubber rod with silk, the charge left on the rod was rubber rod with silk, the charge left on the rod was called negative.called negative.

Like charges repel while unlike charges attractLike charges repel while unlike charges attract..

On the MoveOn the Move

Electrons in the outer rings or shells of atoms are Electrons in the outer rings or shells of atoms are bound more loosely to the nucleusbound more loosely to the nucleus

Such electrons tend to break free from the nucleus Such electrons tend to break free from the nucleus and wander around amongst other nearby atomsand wander around amongst other nearby atoms

Such electrons are called free electronsSuch electrons are called free electrons

Current = ConductionCurrent = Conduction

Such movement of these free electrons creates an electric current Materials with large numbers of free electrons are called electrical conductors. They conduct electrical current. Movement of the electrons physically from one place to another is slow. Transfer of the energy from one electron to another happens fast.

Conductors and InsulatorsConductors and Insulators

In conductors, electric charges are free to move In conductors, electric charges are free to move through the material. In insulators, they are not.through the material. In insulators, they are not.

In conductors:In conductors: The charge carriers are called free electronsThe charge carriers are called free electrons Only negative charges are free to moveOnly negative charges are free to move When isolated atoms are combined to form a When isolated atoms are combined to form a

metal, outer electrons of the atoms do not metal, outer electrons of the atoms do not remain attached to individual atoms but remain attached to individual atoms but become free to move throughout the volume become free to move throughout the volume of the materialof the material

Other Types of ConductorsOther Types of Conductors

ElectrolytesElectrolytes Both negative and positive charges can moveBoth negative and positive charges can move

SemiconductorsSemiconductors In-between conductors and insulators in their In-between conductors and insulators in their

ability to conduct electricityability to conduct electricity Conductivity can be greatly enhanced by Conductivity can be greatly enhanced by

adding small amounts of other elementsadding small amounts of other elements Requires quantum physics to truly Requires quantum physics to truly

understand how they workunderstand how they work

Simple CircuitsSimple Circuits

Don’t let the name fool youDon’t let the name fool you Bottom line: For electric current to flow, Bottom line: For electric current to flow,

there has to be a complete pathway for there has to be a complete pathway for it…a complete circuit.it…a complete circuit.

Closed and Open CircuitsClosed and Open Circuits

Closed Circuit - an unbroken path of conductors through which electric current flows

Open Circuit - a circuit with a break in the conductive path, so no current flows

Now, let’s play… “Know Your Electrical Symbols!”

Know Your SymbolsKnow Your Symbols

Battery or Power Supply

Resistor

Capacitor

Switch

Conductive Wire

Series CircuitsSeries Circuits

An electrical circuit with only one path for the electrical current to follow

Parallel CircuitsParallel Circuits

An electrical circuit that provides more than one path for the electrical current to follow.

Static ElectricityStatic Electricity

Who hasn’t rubbed a balloon on their hair and stuck it to the wall?

Buildup of charge (static, not moving)in one place.

Charge can be either positive or negative

Beware of Door Knobs That BiteBeware of Door Knobs That Bite

More apt to happen in dry weather…why?

electricity you light up my life! what is electricity? electricity is one of the two long-range...

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