Video Summaries
Physics Level 3
Electricity
DC Circuits
Whatyouneedtoknow
($-./-012)Ω
InternalResistance
' = )*
Kirchhoff’scurrentlaw:
5$
Thecurrententeringa
junction,mustequal
thecurrentleavinga
−5$
10Ω
junction
Kirchhoff’svoltagelaw:
Voltagesaroundaclosedloopmustaddtozero
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12$
(:)issame
emf
47
+5$
46
45
Video Summaries
Capacitors – Part 1
What you need to know
Capacitance,',isthe
abilitytoholdcharge,(:
+ +
+
+ +
+
+
+
1234(1)
+
+ +
*+*, '=
.
12&
−
( = '&
1
/ = (&
2
0
−
−
− − −−
−
−
−
− −+ −
Dielectric isaninsulating(non-conducting)layer
betweenplates
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Capacitors – Part 2
Series:lowerscapacitance
What you need to know
1
1
1
=
+ +
/0 /2 /4
Charging
12$
99%
98%
95%
87%
Parallel: increasescapacitance
63%
/0 = /2 + /4 +
0$
%
%
1%
%
2%
%
3%
%
4%
TimeConstant:% = 5/
5% Charged
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Video Summaries
Inductors – Part 1
∆
- = ./
)
=
−
∆,
1 (
∆'
!
=
&'
) = −&
2
∆,
) = opposingvoltage(0)
- = Flux(12)
& = Inductance(3)
∆ currentà
∆magneticfieldà opposingvoltageà opposingcurrentà opposingmagneticfieldà …
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Inductors – Part 2
6
12#
=
What
you
need
to
know
7
12#
200Ω
2
63%
87%
95% 98%
∆1
−4
99%
0#
12345- Noopposingvoltage
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What you need to know
Aninductoropposeschange
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Video Summaries
AC Circuits – Part 1
What you need to know
Voltage
Capacitor
<⁄ cycle(90degrees)behind
=
-./0 = 1-2.3
Peakvoltage
!"# = 1
2
2CDEFDGEC(Ω),LM = 1
NO
×)*+,
Inductor
<⁄ cycle(90degrees)ahead
=
2CDEFDGEC(Ω),LP = NQ
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AC Circuits – Part 2
What you need to know
Phase
• Inductorandcapacitorreactance,!,(andvoltage,")
are180 0 outofphase(opposite).
• Thismeanstheycanceleachotherout.
!
#%
Impedance
"
!
#$
!
!
• Impedanceis“overallresistance”ofthecircuit
• Impedance(')=Resistance(()+Reactance(!)
• UseSOHCAHTOAandPythagorastofind
Resonance
• When!) and!* areequalsizes,theycanceleach
otherFULLY.ThismeansNOreactance(' = ()
• Minimumimpedance(')meansamuchhigher
current(" = ,')
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