Electricity Theory

8/13/2019 Electricity Theory

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Electricity TheoryVIR PIV and Capacitors!!!


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EnergyWhen an object is atsome height in a

gravitational field it issaid to have gravitational potentialenergy, PE

g

PE g


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EnergyLike gravitational fields causing masses tohave potential energy, Electric Fields cause

charges to have electr ic potential energy, PE E PE E is a type of mechanical energy ME total = KE + PE g + PE s + PE E


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EnergyTo give something PE you must do work(apply force over a distance) on the

something (raising up in g-field)For PE E to occur a F E must be applied byeither

a. An E-Field (uniform) b. A pair of charges


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EnergyUniform E-field

AB

Line Color

Red: E-Field

Black: Equipotential lines

Blue: charge displacement

E

W PE Fd F Eq

PE qEd


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EnergyPair of Charges

1 2

2

1 2

c

E c

W PE Fd

q q F k

r

q q PE k r


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Electric Potential

Any point in an electric fieldis said to have Electric

Potential, V.However, only a Difference in PE is measurable(remember zero point) so wetalk of electric potentialdifference AKA potentialdifference, V.

E PE V q

PE V

q

unit Volt, V

J1V=1

C


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Potential Difference


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Potential Difference


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Potential DifferenceBack to the zero point

A convenient zero point to chose in a circuit or anyelectric system is the ground


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Battery (cells)A battery produceselectricity bytransforming chemicalenergy into electricalenergy


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BatteryCarbon Electrode

Zinc Electrode

Sulfuric Acid

+


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CapacitorA capacitor is a storehouse of charge and energy thatcan be reclaimed when needed for a specificapplication

A capacitor will only charge to the potentialdifference between the terminals of the battery


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CapacitanceCapacitance, C: The ability of a conductor tostore energy in the form of electrically

separated chargesCapacitance is the ratio of charge to potentialdifference

QC V

unit Farad, FC

1F=1V


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CapacitanceCapacitance depends on size and shape

0

AC d

2-12

0 2 permittivity of free space, 8.85x10

Area of one plate

d distance between plates

C

Nm A


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CapacitorEnergy stored in acapacitor

21 12 2

U energy QV CV


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Electric CurrentMovement of electric chargeRate of charge movement

Q I

t

unit Ampere, A

C1A=1 s


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Charge Movement


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Charge Movement


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Circuit Analogy


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Types of CurrentAC Alternating current chargescontinuously change direction forward and

back at 60 HzExample: outlets (approx 120 V)DC Direct current charges move in onedirection

Example: batteries

AC-DC Debate births the Electric Chair
http://www.correctionhistory.org/auburn&osborne/miskell/html/auburnchair_moran.htmlhttp://www.correctionhistory.org/auburn&osborne/miskell/html/auburnchair_moran.htmlhttp://www.correctionhistory.org/auburn&osborne/miskell/html/auburnchair_moran.htmlhttp://www.correctionhistory.org/auburn&osborne/miskell/html/auburnchair_moran.html


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ResistanceResistance is the impedance of the motion ofcharge through a conductor

The ratio of potential difference across aconductor to the current it carries

V R I

2

unit ohm,

V Js1 1 1

A C


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Ohms Law

V IR


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ResistanceDepends on: Length, cross sectional area,material, and temperature

L R

A

2

resistivity, m

L length, m

A cross sectional area, m


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Resistance and Temp


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Resistance and Thickness


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ResistorAn electronic elementthat provides a specifiedresistance.A current or voltageREGULATOR


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Power (its Electric!) Power : Rate at which work is done. OR Rateat which energy is transformed

Electric Power : The rate at which chargecarriers convert PE E into non-mechanicalenergy

P IV unit watt, WJ1 W = 1s


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Reading and HomeworkRead Chapter 17

pp 593 - 625HW due on test day:

p 599 1-3; p 601 2, 3, 5-9; p 607 1 4 (B); p609 1 5 p 615 1 6; p 616 2-4, 7,9 p 621 1 5

Extra Practice p 626 628 11, 20 54

Electricity Theory

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