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Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Lecture 13
Chapter 28
Resistors in Series and Parallel
Physics II
I wish my clicker could mute him
Equivalent resistance,.. blah, blah, blah
Course website:https://sites.uml.edu/andriy-danylov/teaching/physics-ii/
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Today we are going to discuss:
Chapter 28:
Section 28.1-6 Resistors 28.7 (Example 28.29)
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Circuit Elements
Slide 31-22
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Resistorsin series/parallel
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
+ +
Resistors in ParallelConsider three resistors connected in parallel.
I
Real
circ
uit
Equi
vale
nt c
ircui
t
ΔV
Resistors in parallel have the same potential difference, ΔV
I + +
;
We have replaced 3 resistors with an “equivalent” resistor.
+ +
Conservation of current
Req is inserted without changing the operation of the circuit, so I and ΔV are same as in the real circuit
Equivalent resistance of resistors in parallel.
=
I1
I2
I3
Ohm’s law;
ΔV
=
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
+ +
Resistors in SeriesConsider three resistors connected in series.
Rea
l cir
cuit
Equ
ival
ent c
ircu
it
ΔV
+ +
Ohm’s law ∆
Req is inserted without changing the operation of the circuit, so I and ΔV are same as in the real circuit
Equivalent resistance of resistors in series.
ΔV
ΔV1 ΔV2 ΔV3
∆∆
+ +
Areheadlightwired: A)inparallel?
B)inseries?
ConcepTest Headlights
ConcepTest Resistors I
ThebatterycurrentIis
A)3A
B) 2A
C) 1A
D) 2/3A
E) ½A
=2/3 A
+
ConcepTest Resistors II
ThebatterycurrentIis
A)3A
B) 2A
C) 1A
D) 2/3A
E) ½A
=3 A
+
=4
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Exa
mpl
e:
Ana
lyzi
ng a
com
plex
cir
cuit
a)Find the equivalent resistance.b)Find the current through and the potential difference across each of the resistors in the circuit.
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Real batteries
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Give me a break! I do it as fast as I
can!
Real Batteries. Todriveacurrentinacircuitweneeda“chargepump”,adevicethatbydoingworkonthechargecarriersmaintainsapotentialdifference.Let’slookatagravitationalanalogofabattery:
Apersondoesworktomaintainasteadyflowofballsthrough“thecircuit”.However,thisguycannotmoveballsinstantaneously.Ittakestime.Sothereisanaturalhindrancetoacompletelyfreeflow.Todescribethishindrancewecanintroducetheinternalresistance,r.Itisinsideabatteryanditcannotbeseparatedfromthebattery.
Pot. difference of a battery without an internal resistance is called an electromotive force.(EMF, ε)
∆Terminal voltage
(Internal resistance)
Department of Physics and Applied PhysicsPHYS.1440 Lecture 13 A.Danylov
Thank you