Marti Andreski De La Salle HS

• ElectricityElectricity comes from the Greek comes from the Greek word “elektron”, (e-) meaning word “elektron”, (e-) meaning ““amberamber” (amber is petrified tree ” (amber is petrified tree resin; when rubbed w/cloth, attracts resin; when rubbed w/cloth, attracts small pieces of leaves or dust) small pieces of leaves or dust)

• ElectricityElectricity means “stream of moving means “stream of moving electrons” but really - the e-‘s electrons” but really - the e-‘s and transfer their charge to the and transfer their charge to the next e- next e-

• atomic structure:atomic structure:

BackgroundBackground

wiggle

Classes of MatterClasses of Matter

• a. a. conductorsconductors - charges are - charges are freefree to to migrate; ie: metals (because they migrate; ie: metals (because they have “sea” of e-‘s)have “sea” of e-‘s)

• b. b. insulatorsinsulators - charges are - charges are not freenot free to migrate; ie: non-metals; since e- to migrate; ie: non-metals; since e- tightly bound to nucleus; and few tightly bound to nucleus; and few e-‘s are available for conductione-‘s are available for conduction

• c. c. semiconductorssemiconductors - poor - poor conductors; conductivityconductors; conductivity changes changes with environment (T); ie: Si, Ge, Cwith environment (T); ie: Si, Ge, C

Laws of Electric ActionLaws of Electric Action

• a. a. Law of Conservation of Electric Law of Conservation of Electric Charge:Charge: “the net amount of “the net amount of electric charge produced by any electric charge produced by any process is zero”process is zero”

Laws of Electric ActionLaws of Electric Action

• b. b. Like chargesLike charges repelrepel; ; unlike unlike charges attractcharges attract ea. other ea. other

ChargeCharge

• The charges we’re talking about The charges we’re talking about are measurableare measurable

• Coulomb – the SI unit of Coulomb – the SI unit of electrical charge electrical charge

• 1 C = 6.25 x 101 C = 6.25 x 101818 electrons or electrons or protonsprotons

• 1 e- = 1.60 x 101 e- = 1.60 x 10-19-19 C C

Coulomb’s LawCoulomb’s Law

• ““the magnitude of the force between the magnitude of the force between two charges, a and b, separated by a two charges, a and b, separated by a distance d, is proportional to the distance d, is proportional to the magnitude of the charges and magnitude of the charges and inversely proportional to the square inversely proportional to the square of the distance” (q = “charge”)of the distance” (q = “charge”)

• F ~ qF ~ qaaqqb so therefore: b so therefore: F = F = KK q qaaqqbb

• dd2 2 dd22

• KK = 9.0 x 10 = 9.0 x 1099 N N..mm22/C/C22

Symbols and UnitsSymbols and Units

UnitUnit SymbolSymbol

Charge (q)Charge (q) coulombcoulomb CC

DistanceDistance metersmeters mm

forceforce NewtonNewton NN

Application of Coulomb’s Application of Coulomb’s LawLaw

• Example: two charges are separated by 3.0 cm. Object A has a Example: two charges are separated by 3.0 cm. Object A has a charge of +6.0charge of +6.0C, while object B has a charge of +3.0 C, while object B has a charge of +3.0 C. What C. What is the force on object A? (text, p. 474)is the force on object A? (text, p. 474)

• Sketch of problem: Sketch of problem: A B3cm

+6.0C +3.0C

Given:

qA = +6.0 C

qB = +3.0 C

dAB = 0.030m

FB on A = ?

Strategy:

Use Coulomb’s Law. Do not include signs. The direction of the force depends on the vector diagram. (In this case, it’s the FB acting on A, so it’s to the “left”.AFB on A

Types of ElectricityTypes of ElectricitySTATIC CURRENT

DefinedDefined ““electricity at electricity at rest” or, rest” or, better, “net better, “net electric electric charge”charge”

““electricity electricity traveling traveling through through conductors and conductors and made to perform made to perform useful work (ie: useful work (ie: batteries, batteries, outlets)outlets)

InvolvesInvolves High Voltage High Voltage at Low Currentat Low Current

Low Voltage at Low Voltage at High CurrentHigh Current

Types/Types/

ExampleExampless

Walking across Walking across carpet; carpet; LightningLightning

AC AC = alternating = alternating current (outlets)current (outlets)

DCDC = direct = direct current current (batteries)(batteries)

Types of ElectricityTypes of Electricity

van de Graaf Generatorvan de Graaf Generator

• http://http://www.mos.org/sln/toe/VDG_workwww.mos.org/sln/toe/VDG_works.movs.mov

•http://www.eskimo. com/~billb/miscon/ele-map.html

Comparison of Voltage vs. Current

Static BuildupStatic Buildup

• Known to ruin electronic Known to ruin electronic equipmentequipment

• Prevention: wear leather shoes; Prevention: wear leather shoes; increase humidity above 60%; use increase humidity above 60%; use antistatic liquid; use ionizer fans; antistatic liquid; use ionizer fans; coat shoes with Al; wear special coat shoes with Al; wear special wrist strapswrist straps

• Can even be a source of igniting Can even be a source of igniting gasoline vapors gasoline vapors

3 Main Sources of 3 Main Sources of ElectricityElectricity

•A. FrictionA. Friction•B. ChemicalB. Chemical•C. GeneratorC. Generator

A. FrictionA. FrictionProduces Produces staticstatic electricity which can be very electricity which can be very

HIGH VOLTAGE but very LOW CURRENT HIGH VOLTAGE but very LOW CURRENT (“safe” but hurts!)(“safe” but hurts!)

• Static chargesStatic charges are positive and negative; are positive and negative; term coined by Ben Franklin (1706-1790) term coined by Ben Franklin (1706-1790) who arbitrarily chose glass + and therefore who arbitrarily chose glass + and therefore plastic would be - (no plastic at the time)plastic would be - (no plastic at the time)

• Positive chargePositive charge - when a glass rod is - when a glass rod is rubbed with silk, it is said to have a + rubbed with silk, it is said to have a + charge (Since e-‘s are lost by the glass to charge (Since e-‘s are lost by the glass to the silk which is now -‘ly charged)the silk which is now -‘ly charged)

• Negative chargeNegative charge - when a rod of rubber or - when a rod of rubber or plastic is rubbed with fur or wool, it is said plastic is rubbed with fur or wool, it is said to be -‘ly charged (the rod took the e-‘s to be -‘ly charged (the rod took the e-‘s from the fur or wool leaving the rod with from the fur or wool leaving the rod with more e-‘s than protons and the fur or wool more e-‘s than protons and the fur or wool with more protons than e-‘s)with more protons than e-‘s)

Electrostatic SeriesElectrostatic Seriesaka: Triboelectric Sequenceaka: Triboelectric Sequence• [from - to + OR from GAIN e- easily to [from - to + OR from GAIN e- easily to

LOSE e- easily]LOSE e- easily]• saran wrap, hard rubber, Teflon, plastic, saran wrap, hard rubber, Teflon, plastic,

Pt, Au, sulfur, rubber balloon, styrofoam, Pt, Au, sulfur, rubber balloon, styrofoam, polyethylene, misc. metals; amber, hard polyethylene, misc. metals; amber, hard wax, Lucite?, cork, wood, cotton, paper, wax, Lucite?, cork, wood, cotton, paper, felt, human hair/skin, silk, lead, cat fur, felt, human hair/skin, silk, lead, cat fur, quartz, wool, nylon, mica, glass, (Lucite?) quartz, wool, nylon, mica, glass, (Lucite?) rabbit fur rabbit fur

• Why is there more static in winter than in Why is there more static in winter than in summer? summer?

• HH22O molecules are polar; attract e-‘sO molecules are polar; attract e-‘s

Demos – Static Demos – Static ElectricityElectricity

Demo Observation ExplanationRubber Rod in stream of water

Rubber rod, fur, water

Butterfly and styrofoam

Butterfly and rubbed styrofoam

Styrofoam Balls – each with same charge

Styrofoam Balls – one rubbed with fur

B. ChemicalB. Chemical

• when 2 different elements come when 2 different elements come together, one will always have a together, one will always have a greater ability to give up e-‘s than greater ability to give up e-‘s than the other. (see St’d Reduction the other. (see St’d Reduction Potentials table)Potentials table)

• That can be used to get charges That can be used to get charges flowing from one element to another flowing from one element to another (that is what electricity is all about)(that is what electricity is all about)

• This is how it works…This is how it works…

The Zn-Cu CellThe Zn-Cu Cell• Zn in a sol’n of Zn in a sol’n of

ZnSOZnSO44

• (this is the (this is the ANODE since ANODE since OXIDATION, the OXIDATION, the LOSS OF LOSS OF ELECTRONS, ELECTRONS, occurs) occurs)

•Cu in a Cu in a sol’n of sol’n of CuSOCuSO44 (this (this is the is the CATHODE CATHODE since since REDUCTIOREDUCTION, the GAIN N, the GAIN OF OF ELECTRONELECTRONS, occurs) S, occurs)

•Salt Bridge – allows ions to transfer back & forth, Salt Bridge – allows ions to transfer back & forth, completing the circuitcompleting the circuit

•Wire & Meter – Wire & Meter – electric charge electric charge goes thru & is goes thru & is measuredmeasured

Zn loses 2e- to the solution Zn+

2

2e-

Cu+2

AnimationAnimation

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/CuZncell.html

What happens?What happens?• Zn wears away (oxidizes or rusts) while Cu Zn wears away (oxidizes or rusts) while Cu

builds upbuilds up• stronger batteries (higher Voltage) are made stronger batteries (higher Voltage) are made

with substances that are FARTHER away from with substances that are FARTHER away from each other on the chart since there each other on the chart since there is GREATER POTENTIAL is GREATER POTENTIAL DIFFERENCE (think of the roller coaster hill DIFFERENCE (think of the roller coaster hill being higher!)being higher!)

• DEMO 2: Zn/Mn Sample Battery: DEMO 2: Zn/Mn Sample Battery: • Zn casing (anode)Zn casing (anode)• Cardboard wrapCardboard wrap• Mn pasteMn paste• Carbon rod; button (cathode)Carbon rod; button (cathode)

SRP : 25oC and 1.0M aqueous

Li+ + e- Li(s) -3.05Cs+ + e- Cs(s) -2.92K+ + e- K(s) -2.92Rb+ + e- Rb(s) -2.92Ba2+ + 2 e- Ba(s) -2.90Sr2+ +2 e- Sr(s) -2.89Ca2+ + 2 e- Ca(s) -2.87Na+ + e- Na(s) -2.71Mg2+ + 2 e- Mg(s) -2.37Be2+ + 2 e- Be(s) -1.70Al3+ + 3 e- Al(s) -1.66Mn2+ + 2 e- Mn(s) -1.18Zn2+ + 2 e- Zn(s) -0.76Cr3+ + 3 e- Cr(s) -0.74Fe2+ + 2 e- Fe(s) -0.44Cr3+ + e- Cr2+ -0.41Cd2+ + 2 e- Cd(s) -0.40Tl+ + e- Tl(s) -0.34Co2+ + 2 e- Co(s) -0.28Ni2+ + 2 e- Ni(s) -0.25Sn2+ + 2e- Sn(s) -0.14Pb2+ + 2 e- Pb(s) -0.13

2 H+ + 2 e- H2(g) 0.00S(s) + 2 H+ + 2 e- H2S (g) 0.14Sn4+ + 2 e- Sn2+ 0.15Cu2+ + e- Cu+ 0.15Cu2+ + 2 e- Cu(s) 0.34Cu+ + e- Cu(s) 0.52I2(s) + 2 e- 2 I- 0.53Fe3+ + e- Fe2+ 0.77Hg2

2+ + 2 e- 2 Hg(l) 0.79Ag+ + e- Ag(s) 0.80Hg2+ + 2 e- Hg(l) 0.852 Hg2+ + 2 e- Hg2

2+ 0.92Br2(l) + 2 e 2 Br- 1.07O2(g) + 4 H+ + 4 e- 2 H2O(l) 1.23Cl2(g) + 2 e- 2 Cl - 1.36Au3+ + 3 e- Au(s) 1.50Co3+ + e- Co2+ 1.82F2(g) + 2 e- 2 F -

2.87

More easily oxidized

(Give up e- easier)More easily reduced

(Take up e- easier)

Using the SRP Chart to Determine Cell VoltageThe pair combined is

Zn and CuThere are 3 locations for Cu; which is used?We have to know the reaction. Cu+2 ions are coming out of solution and becoming Cu metal, so…

Cu+2 + 2e- CuSince Zn is higher on the table, it is the oxidized half; Cu is reduced. NOTE: is the form Zn+2 + 2e- Zn written as an oxidation?

(LOSS OF e- = oxidation!)

C. GeneratorC. Generator

• This will be discussed in detail in the This will be discussed in detail in the Electromagnetism unitElectromagnetism unit

• Basically, since electricity is a flow of Basically, since electricity is a flow of electric charge and any time electrons electric charge and any time electrons can flow that’s electricity, electrons can can flow that’s electricity, electrons can be made to flow in a wire that is put in a be made to flow in a wire that is put in a magnetic field and turned. If there are magnetic field and turned. If there are a lot of turnings of wire and continuous a lot of turnings of wire and continuous movement of the magnet, e- keep movement of the magnet, e- keep flowing and electricity is generated.flowing and electricity is generated.