Chapter 1 Introduction

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Chapter 1 Introduction
Introduction to Circuits Theory and Digital
Electronics
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1.2 Circuits, Currents, and Voltages
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• The circuit consists of
• A battery
• A switch
• The headlamps
• Wires

• Switch is closed
• Current flows through the circuit
• Switch is open
• The current does not flow

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Electrical Circuits (??)

• An electrical circuit consists of various type
  of circuit elements (????) connected in closed
  path by conductors (??).

(??)
(??)
(???)
(??)
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Circuit Elements
??
??
????
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Electrical Current (??)

• Electrical current is the time rate of flow of
  electrical charge (?????????) through a conductor
  or circuit element. The units are amperes (A),
  which are equivalent to coulombs (??) per second
  (C/s).

Note The charge on an electron is
C
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Electrical Current

• q(t) ??? t ???? (net charge)
• Positive charge crossing in the reference
  direction (????) is counted as a positive
  contribution to net charge

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Example 1.1 Determine Current Given charge
Given
Sketch q(t) i(t) to scale vs. time.
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Sol
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Reference Directions (????)

• In analyzing electrical circuits, we may not
  initially know the actual direction of current
  flow.
• Therefore, we start by assigning current
  variables and arbitrarily selecting a reference
  direction.

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Direct Current (DC, ??? )Alternating Current
(AC, ??? )

• When a current is constant with time, we say
  that we have direct current, abbreviated as dc.
  On the other hand, a current that varies with
  time, reversing direction periodically, is called
  alternating current, abbreviated as ac.

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.
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Double-Subscript Notation
We can use double subscripts to define the
reference direction for the current.
iab ? a ?? b ???
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Voltages (??)

• The voltage ?????(unit of charge)???????????????
  ?????? (transferred energy)?
• Voltage ?? volts (V), joules per coulomb (J/C,
  ??/??)

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Voltage Direction
a
??
??
b

• Vab ???????? ?? a ????? b ?????, Vab - Vba ?
• ??????????-??????????
• ??????- ??????????????

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Voltage Direction
a
Note
b
??
??
???
??
??
???
??
?????????????????
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Note

• Voltage is measured across the ends (??) of a
  circuit element.
• Current is a measure of charge flow through the
  element.

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1.3 POWER (??) AND ENERGY(??)

• ?? (energy) ??(J)
• ??(power) p ????????? J/sec, ?????(W, watt)
• i C/sec, v J/C,

p(t) v(t)i(t)

• ????? w (energy between t1 and t2)

(J, ??)
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Prefixes Physical Quantities
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1.4 KIRCHHOFFS CURRENT LAW (KCL)

1. ????(node)????(net current)?0.
2. ?????????0.
3. ???????? ?????????

node
Note ?????????????????????????
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KIRCHHOFFS CURRENT LAW (KCL)
Node a

????????
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???? (series circuits)
Node 1
Node 2
?????????
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Excise 1.7 Use KCL to find the unknown currents
in Fig. 1.21
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1.5 KIRCHHOFFS VOLTAGE LAW (KVL)

• ???????????(closed loop),???????.

Note ??(loop)??????????????????????????(close
path)?
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Loop 1
Loop 2
Loop 3
????????
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???? (parallel circuits)
L1
L2
?????????
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Excise 1.9 Using KVL to find vc ve
Excise 1.10 Identify elements that are in
parallel. Identify elements that
are in series.
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1.6 Circuit Elements

• Conductors (??)
• Voltage sources (???)
• Current source (???)
• Resistors (??)

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Conductors (??)

• ????????(ideal conductors) ??????0.
• ???????????shorted circuit (??),????? node.
• ???????????????????(open circuit).

open/closed
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Ideal Voltage Source (?????)

• ??(??)??? (ideal independent voltage
  source)?????????,??????????????
• ??????????

DC
AC
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Dependent Voltage Source (?????)

• ?????(dependent voltage source)???????????????????
  ,????????(controlled voltage source)?
• ???
• ????(voltage-controlled)???
• ????(current-controlled)???
• ????????

?????
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??/???????

• ???????(voltage-controlled voltage
  source)?????????????????????
• ???????(current-controlled voltage
  source)?????????????????????

???? (gain factor)2 (V/V)
???? 3 (V/A)
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Independent Current Sources (?????)

• ???????????????,??????????????
• ?????????,???????????

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Dependent Current Source (?????)

• ?????(dependent voltage source)???????????????????
  ??,????????(controlled current source)?
• ???
• ???????
• ???????
• ????????

?????
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??/???????
???? (gain factor)3 (A/V)
???? 2 (A/A)
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?? (Resistor)

• ????????????????
• ????(Ohms law)
• Passive reference configuration???????????????????
  ,?????????????,???????????

a
?? (V/A)
b
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?? (Conductance)
(??)
siemens (A/V)
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??????????

• ??????????????,??????,??????
• ??????????? (resistivity)
• ????

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1.7 Introduction to Circuits
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Using KVL, KCL, and Ohms Law to Solve a Circuit
Ohms Law
KCL
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Ohms Law
KVL