FOWLER CHAPTER 2 LECTURE 3 ELECTRICAL QUANTITIES AND UNITS.

FOWLER CHAPTER 2LECTURE 3 ELECTRICAL QUANTITIES

AND UNITS

CHAPTER 2 ELECTRICAL QUANTITIES AND UNITS

COULOMB BASE UNIT OF CHARGE= ELECTRONSCHARGE SYMBOL =QABBREVIATION =C

ELECTRIC CURRENT (I) MOVEMENT OF CHARGED PARTICLES IN A SPECIFY DIRECTION

CAN BE +OR- LIKE CHARGES REPELUNLIKE CHARGES ATTRACK

+ CHARGE CAN BE + ION

- CHARGE IS AN ELECTRON

THESE CHARGES CAN MOVE THRU SOLIDSLIQUIDS OR GASES IN OUR MOST COMMON CONDUCTOR COPPER ONLY ELECTRONS CAN MOVE

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CURRENT= Qt CHARGETIME

AMPERE ONE COULOMBSEC OR ELECTRONS SEC

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SYMBOL I WAS CHOSEN BECAUSE IT WAS THOUGH TO REPRESENT THE INTENSITY OF ELECTRICITY IN A WIRE CURRENT MOVES AT LESS THAN THE SPEED OF LIGHT IN ANY WIRE

WHEN A ELECTRIC FIELD IS PLACED ACROSS A WIRE SAY FROM A BATTERY VALENCE ELCTRONS MOVE FROM ATOM TO ATOM CREATING + AND- IONS WHICH UNDER THE INFLUENCE OF THE ELECTRIC FIELD ALLOWS CURRENT TO FLOW

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Basic Electricity - What is an amp httpwwwyoutubecomwatchv=8gvJzrjwjds

CURRENT FLOWING IN THE SAME DIRECTION ALL THE TIME IS KNOWN AS DIRECT CURRENT

+

_

0TIME

VOLTAGE

CURRENTS IN GASES

IN GASES UNDER THE INFULENCE OF A STRONG ELECTRIC FIELD + AND ndash CHARGES ARE FORMED ie + IONS AND ELECTRONS THIS IS CALLED IONIZATION

+-

++

++

--

--

- +

+

NEON FILLED TUBE IN A NEAR VACUUM NEON ATOM HAS 8 VALENCE ELECTRONS IN ITS OUTER RING

METAL PLATEMETAL PLATE

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AGAIN + AND ndash CHARGES SERVE AS CURRENT CARRIES UNLIKE GASESIN LIQUIDS BOTH + AND - CURRENT CARRIES ARE IONS

CURRENTS IN LIQUIDS

METAL PLATES

NaCl SOLUTION

-

-

-- -

-

+

+

++

++ +

- ARE Cl IONS

+ ARE Na IONS

A LIQUID THAT CAN CARRY CURRENT IS CALLED AN ELECTROLYTE (eg SEA WATERSULFURIC ACID IN CAR BATTERIES)

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CURRENTS IN VACUUM

IN THIS CASE AN ELECTRON TUBE IS USED AS AN EXAMPLE

CATHODES ARE COATED WITH THORIUMBARIUM OR STRONTIUM

+

-

THERMIONIC EMISSION EMITTION OF ELECTRONS FROM A HEATED PLATE AS THE PLATE IS HEATED IT EMITS ELECTRONS WHICH ARE DRAWN TO THE POSITIVE PLATE BY THE ELECTRIC FIELD CREATED BY THE BATTERY ON A SIMPLE SCALE THIS IS HOW A CRT WORKS

+

-

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ELECTRON MOVEMENT IN A TUBE FILAMENT

CLOSE UP VIEW OF A TUBE FILAMENT

VOLTAGE=EMF(ELCTROMOTIVE FORCE)=POTENTIAL DIFFERENCE(All mean the same thing)

KINETIC VS POTENTIAL ENERGY

KINETIC ENERGY OF MOTION OF AN OBJECTPOTENTIAL ENERGY STORED ENERGY OF AN OBJECT AT REST

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STATIC ELECTRICITY IS POTENTIAL ENGERY (PE)

STATIC SPARK CONVERTS PE OF THIS SPARK INTO HEAT AND LIGHT

IN ELECTRICITY THE PE IS DUE TO THE ELECTRIC FIELD AND THE CHARGE SEPARATION BETWEEN TWO OBJECTS

YOU TUBEA cell phone and static electricity

Bill Nye The Science Guy on Static Electricity

wwwyoutubecomwatchv=gct1BmKNvU0wwwyoutubecomwatchv=Z-77IzaXGcg

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high voltages on a hollow metal globe on the top of the stand It was invented by American physicist Robert J Van de Graaff in 1929 The potential difference achieved in modern Van de Graaff generators can reach 5 megavolts

ELECTROSTATIC ATTRACTION BETWEEN 2 CHARGED SPHERErsquoS

httpwwwyoutubecomwatchfeature=fvwpampv=THybl_QGsswampNR=1electric flux animation

httpphetcoloradoeduensimulationballoons

TAKE ELECTROSTATIC PRECAUTIONS WHEN WORKING ON ANY ELECTRONIC EQUIPTMENT

ELECTRIC FIELD LINESSPHERE WITH EXCESS POSITIVE CHARGES

SPHERE WITH EXCESS NEGATIVE CHARGES

THE PE IS DUE TO THE ELECTRIC FIELD AND ELECTRIC CHARGE BETWEEN TWO OBJECTS THIS FIELD CREATES A POTENTIAL DIFFERENCE

AS ELECTRONrsquoS MOVE ACROSS THE ELECTRIC FIELD WORK IS DONE ENERGY IS LOSS MOVING FROM ndash TO +

-

SHOW MU29 13001630 httpwwwyoutubecomwatchv=PeBPPudNpAw

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UNIT OF VOLTAGE (V) VOLT

WE NEED A WAY TO INDICATE THE PE DIFFERENT BETWEEN THE TERMINALSOF OUR BATTERY

ENERGY IS TRANSFORMED BY CHARGES(ELECTRICAL) ACROSS THE BATTERY TERMINAL

SINCE THE BASE UNIT OF ENERGY IS THE JOULE AND THE BASE UNIT OF CHARGE IS THE COULOMB

WE CAN DEFINE VOLTAGE AS JOULECOULOMB

V=JOULECOULOMB

V= ENERGYCHARGE= WQ

OR W=VQ

W(WORK OR ENERGY)= VQ

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EXAMPLE D CELL BATTERIES ARE RATED AT 15V A FLASHLIGHT WITH 2D CELLS = 3 V

WHAT DOES THIS MEAN

WHEN THE FLASHLIGHT IS ON WITH A POTENTIAL DIFFERENT OF 3V

V = JC 3 JOULES OF ENERGY IS CARRIED BY 1 COULOMB OF CHARGE WHICH ARE CONVERTED TO HEAT AND LIGHT

BATTERIES

THERE IS A PE DIFFERENT BETWEEN THE + AND ndash TERMINALS OF THE BATTERY WHEN CURRENT FLOWS WORK IS DONE P E IS CONVERTED INTO ANOTHER FORM OF ENERGY IN THIS CASE AS HEAT IN THE RESISTOR

BATTERY IS DISCHARGING BATTERY IS CHARGING

DIRECTION OF ELECTRON FLOW ELCTRON FLOW IS REVERSED

+

־ +

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POLARITY HELPS TO INDICATE WHICH DIRECTION CURRENT IS FLOWING CAN BE + OR -

WHEN TERMINALS ARE IDENTIFIED ON A ELECTRONIC DEVICE IT IS SAID TO BE POLARIZED

POLARITY MUST BE CORRECT FOR THE DEVICE TO WORK IF THE DEVICE IS CONNECTED BACKWARD IT IS SAID TO BE IN A STATE OF REVERSE POLARITY AND NO CURRENT WILL FLOW

The Mechanical Universe - 31 ndash Voltage Energy and Force 600-8001215-1400

httpwwwyoutubecomwatchv=jnWc_6PqJ6I

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SOURCES OF VOLTAGE

REMEMBER ONE FORM OF ENERGY MUST BE CONVERTED TO ANOTHER TO CREATE VOLTAGEEXAMPLEPOWER PLANT GENERATORS

COAL

NUCLEAR

HYDROELECTRIC

CONVERT MECHANICAL ENERGY INTOELECTRICAL ENERGY

SOLAR

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GEOTHERMAL

OTHER WAYS TO GENERATE ELECTRICITY

CRYSTALS (VIA THE PIEZOELECTRIC EFFECT)

BY VARYING PRESSURE APPLIED TO CRYSTALS CAN CREATE ELECTRICITY USESPHONOGRAPH PICKUPS MICROPHONES

IN MIRCOPHONES SOUND ENERGY IS CONVERED TO MECHANICALENERGY WHICH IS APPIELD TO A CYRSTAL TO CREATE ELECTRICITY

THERMOCOUPLE(SEEBECK EFFECT) THE DIFFERENT IN TEMPERTUREBETWEEN TWO MATERIALS(USUALLY METALS OR SEMICONDUCTORS)CAN BE CONVERTED INTO ELECTRICITY

YOU TUBE Thermocouples httpwwwyoutubecomwatchv=gtO0kQ-PT_0

RESISTANCE OPPOSITION TO CURRENT FLOW IN A MATERIAL ELECTRICAL ENERGY IS CONVERTED INTO HEAT

CONDUCTORS OFFER LITTLE RESISTANCE TO CURRENT FLOW WHY DO TO THE EASE AS WHICH VALANCE ELECTRONS CAN BE RELEASED FROM THE OUTER SHELL OF AN ATOMGOOD CONDUCTORS SILVERGOLDALUMINIUMCOPPERBAD CONDUCTORS RUBBERWOODCERAMIC MATERIAL GLASS

INSULATORS HAVE HIGH RESISTANCE TO CURRENT FLOW

A BAD CONDUCTOR IS A GOOD INSULATOR

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MOST INSULATORS ARE COMPOUNDS OF TWO OR MORE ELEMENTS THEYSHARE ELECTRONSBY COVALENT BONDING(MAKES IT HARDER FOR ELECTRONS TO BE FREED)

METAL CONDUCTORSGLASS INSULATORS

UNIT OF RESISTANCE IS THE OHM Ω

1 Ω AMOUNT OF RESISTANCE IN A MATERIAL WITH 1 VOLT APPLIED WITH A CURRENT FLOW OF 1 AMP

4 FACTORS THAT EFFECT RESISTANCE 1 TYPE OF MATERIAL 2 LENGTH OF OBJECT 3 CROSS SECTIONAL AREA 4 TEMPERATURE OF OBJECT

httpphetcoloradoedusimsresistance-in-a-wireresistance-in-a-wire_enhtml

ALR

AS TEMPERATURE INCREASES SO DOES THE RESISTANCE

TEMP COEFFICENT THE CHANGE IN RESISTANCE OF A MATERIAL AS THE TEMPERATURE INCREASES OR DECREASES

MOST MATERIALS HAVE + TEMP COEFF ie AS TEMP uarr SO DOES THE RESISTANCESOME HAVE ndash TEMP COEFF (EXAMPLE CARBON)

TEMP COEFFICENT IS EXPRESSED AS THE CHANGE OF RESISTANCE(IN OHMS) PER PPM (PART PER MILLION) Cdeg

RESISTIVITYTHE RESISTANCE OF A MATERIAL AS DEFINED BY A CERTAIN SIZE OF THE MATERIAL CAN BE 1cmsup3 1msup3 1ftsup3

THE RESISTIVITY UNIT IS THE Ωcm SEE APPENDIX E P479 THE LOWER THE RESISTIVITY THE BETTER CONDUCTOR IT IS

RESISTIVITY x LENGTHCROSS SECTIONAL AREAA

LR

RESISTORS USED IN CIRCUITS TO CONTROL THE FLOW OF CURRENT

RANGElt1Ω TOgt1 MILLION ΩrsquoSRSISITANCE IN CIRCUIT WIRES IS SO SMALL THAT IT DOSENrsquoT AFFECT THE PERFORMANCE OF THE CIRCUIT

A heating element converts electricity into heat through the process of Joule heating Electric current through the element encounters resistance resulting in heating of the element

httpswwwyoutubecomwatchv=WYcw_DcZsakHow a Toaster Works

Knife into toaster FAIL httpswwwyoutubecomwatchv=So7I70Z0uCU

Most heating elements use Nichrome 8020 (80 nickel 20 chromium) wire ribbon straight or coiled Nichrome 8020 is an ideal material because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time Material beneath this layer will not oxidize preventing the wire from breaking or burning outUsed in common items such as toasters and hair dryers furnaces for industrial heating floor heating roof heating pathway heating to melt snow dryers etc

POWERENERGY IS ABILITY TO DO WORK A GAGE OF HOW ENERGY IS CONVERTED FROM ONE FORM TO ANOTHERPOWER CAN ALSO BE THOUGHT OF AS THE RATE OF USING ENERGY OR WORK

HOW DO WE MEASURE THIS IN A PRACTICAL WAYLIKE THIS HOW MUCH ENERGY IS BEGING USED IN A GIVEN TIME

UNIT OF POWER IS THE WATT (W)

WATT = 1 JOULE SECOND = 1 JS POWER (P) =Wt = ENERGY TIME

WATTSECOND = 1 J SS =1 J JOULE IS A TINY AMOUNT OF ENERGY POWER COMPANIES USES KILOWATT-HOUR INSTEAD OF WATTSECOND

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OLD ANALOG POWER METER NEW DIGITAL POWER METER