28 Circuits

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28 Circuits
28-1 Pumping Charges
Emf device,is said to provide an emf e
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28-2 Work,Energy,and Emf
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An idea emf device is one that lacks any
Internal resistance to the internal movement if
charge from terminal to terminal.
A real emf device,such as any real battery, has
internal resistance to the internal movement of
charge.
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The actual direction of the current in
the circuit is determined by the battery with
the larger emf.
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28-3 Calculating the Current in a Single-Loop
Circuit
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Energy Method
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Potential Method
LOOP RULEThe algebraic sum of the charges in
potential encountered in a complete traversal of
any loop of a circuit must be zero.
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RESISTANVE RULEFor a move through a Resistance
in the direction of the current,the Change in
potential is iRin the opposite Direction it is
iR.
EMF RULEFor a move through an ideal emf Device
in the direction of the emf arrow,the Change in
potential is ein the opposite Direction it is
e.
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28-4 Other Single-Loop Circuits
Internal Resistance
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Resistances in Series
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28-5 Potential Differences
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To find the potential difference between any two
points in a circuit,start at one point and
traverse the circuit to the other, following any
path,and add algebraically the changes in
potential that you encounter.
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Power,Potential,and Emf
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Sample Problen28-1
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28-6 Multiloop Circuits
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JUNCTION RULEThe sum of the currents Entering
any junction must be equal to the Sum of the
currents leaving that junction.
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Resistances in Parallel
When a potential difference V is applied
across resistances connected in parallel,the
resistance all have that same potential different
V.
Resistances connected in parallel can be
replaced with an equivalent resistance Req that
has the same potential difference V and the same
total current I as the actual resistances.
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Sample Problem 28-2
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(a)
Step one
Step two
Step three
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Step four
Step five
Step six
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(b)
Step one
Step two
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(c)
Step one
Step two
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Sample Problem 28-3
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Step one
Step two
Step three
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Step four
Step five
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28-7 The Ammeter and the Voltmeter
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28-8 RC Circuits
Charging a Capacitor
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A capacitor that is being initially acts like
ordinary connecting wire relative to the charging
current.A long time later,it acts like a broken
wire.
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The Time Constant
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Discharging a Capacitor
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Derivation of Eq.28-30
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Sample Problem 28-5
(a)
Step one
Step two
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(b)
Step one
Step two
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