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OverviewElectrostaticsElectric PotentialDielectrics and CapacitanceElectric CurrentDC CircuitsMagnetism
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ElectrostaticsCharge is carried by subatomic particles
protons, electrons!
" 99# o$ all charged e$$ects caused by electrontrans$er
Charging by Conduction
" Physical contactCharging by %nduction" &o physical contact
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Coulomb’s Law'his la( determines the $orce o$ attraction orrepulsion bet(een 2 charged ob)ects
" ε 0 is a constant * permitti+ity o$ $ree space
" Positi+e $orce repulsi+e, negati+e $orce attracti+e
" -emember. $orce is a +ector
F Q Qr
q = 14 0
1 22π ε
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Electric field lines +isualrepresentation o$
an electric $ield1" More lines
stringer $orce
" Point a(ay $rompositi+e, to(ardnegati+e1
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Electric Fields and conductors'he electric $ield inside any conductor is
ero
'he electric $ield is al(ays perpendicularto the sur$ace o$ a conductor
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auss’ LawElectric 3lu . 'he amount o$ an electric $ieldpassing through an area
5auss6 7a(. 'he total electric $lu passingthrough a closed sur$ace is proportional to thecharged enclosed in that sur$ace1
Φ = Qe n c l o s e d
ε 0
Φ = E A c o s θ
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Electric Potential Ener!yElectric Potential energy can be determinedusing mechanics
Electric potential is de$ined as the electricpotential energy per unit charge
∆ U q E d = −
V U q
W q
= = − ∆ ∆U q V = −
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E"ui#otential lines or surfaces n e uipotential sur$ace is a sur$aceo+er (hich all points ha+e the same
potential1" n e uipotential sur$ace must be
perpendicular to the electric $ield
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Potential due to a #oint char!e
V Qr =
1
4 0π ε
" -emember. potential is a scalar
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Ca#acitance capacitor is a de+ice that stores electriccharge1
'he capacitance o$ an ob)ect is de$ined as.
Capacitance is measured in $arads1
C QV
=
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Parallel #late ca#acitors and
dielectrics3or a parallel plate capacitor t(o conductingplates (ith a +acuum bet(een the plates!
$ten, an insulator :no(n as a dielectric isplaced bet(een the plates to enhancecapacitance" Dielectric constant. measures the strength o$ the
dielectric
C Ad = ε 0
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Ca#acitors and ener!y charged capacitor stores an amount o$electric energy gi+en by
" 'his energy can be thought o$ as stored in the electric$ield bet(een the plates1
U Q V = 12
2
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Electric CurrentElectric current is de$ined as the amounto$ charge that $lo(s past a gi+en point in
a second
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Ohm’s Lawhm6s 7a( related the resistance o$ an
ob)ect to the decrease in electric potentialacross a point and the current $lo(ingthrough that point1
RV
I =
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Electric ResistanceElectric resistance is the innate ability o$ amaterial to inhibit the passage o$ electrons1
"Measured in ohms1
" 5i+en by the resisti+ity as (ell as the geometry o$ theob)ect1
R
L
A=
ρ
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Circuits $ emf and terminalvolta!e
de+ice that trans$orms one type o$ energyinto electrical energy is a ;source o$electromoti+e $orce<" em$. the potential di$$erence bet(een the terminals o$ a
battery (hen there is no current $lo(ing to an e ternalsource1
" battery has some internal resistance
" 'he real +oltage o$ a battery is then
V E I r = −
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Resistors in series
=oltage andresistance areadditi+eCurrent is constante+ery(here in aseries circuit
R Re q ii= ∑
V V t o t a l ii
= ∑
I I I t o t a l = = =1 2 . . .
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Resistors in #arallel
Current additi+e=oltage is constant
e+ery(here in aseries circuitMore resistors smaller e ui+alent
resistance1 1
R Re q ii= ∑ I I t o t a l i
i= ∑
V V V t o t a l = = =1 2 . . .
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Com#le% Circuits
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&irchhoff’s rules
>unction rule. t any )unction point, thetotal current into the )unction has to be
e ual to the total current out o$ the )unction17oop rule. 'he sum o$ changes in
potential around and closed loop is ero1
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&irchhoff’s Rules
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'a!netism
E+ery magnet has t(o poles. north andsouth
Magnetic $ield ? magnetic $ield lines.analogous to electric $ield" Direction. points north to south
Electric current mo+ing charge!produces a magnetic $ield
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Force due to ma!netic fields
'he $orce on a charged particle mo+ing througha magnetic $ield
'he $orce in a current carrying (ire immersedin a magnetic $ield
F q v B= s i n θ
F I L B= s i n θ
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Ri!ht hand rule
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Am#ere’s Law
mo+ing charge current! creates a magnetic$ield1
" 3or a long (ire, ∆ l 2 π r
" '(o (ires can attract or repel due to this e$$ect1
" solenoid is a long coil o$ (ire1
B l I ii
e n c l o s e d ∆∑ = µ 0
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Faraday’s Law
changing magnetic $ield induced an em$1
" current produced by an induced em$ mo+es in adirection such that its magnetic $ield opposes the
original change in $lu 7en 6s 7a(!" coil rotating in a magnetic $ield is a good e ampleo$ this1
E N t
= − ∆ Φ
∆
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