ECET 3000
Principles of Electricity
Fall-2012
Chapter 1
Basic DC Circuits
Fall-2012
1
Objectives
• Distinguish between dc and ac and discuss
some of the basic properties of each.
• State and describe the basic circuit variables
including charge, voltage, current, power, and
energy.
• Define resistance and conductance and show
the schematic symbol.
Fall-2012
2
Objectives
• State the properties of the ideal voltage source and
ideal current source models and show their
schematic symbols.
• State and apply Ohm’s law.
• Discuss voltage and current measurements and how
they are made.
• State and apply Kirchoff’s voltage law.
• State and apply Kirchoff’s current law.
Fall-2012
3
Objectives
• Determine equivalent resistance using series
and parallel combinations.
• Analyze a single-loop (series) circuit to
determine all the variables.
• Analyze a single node-pair (parallel) circuit to
determine all the variables.
• State and apply the voltage divider rule.
• State and apply the current divider rule.
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4
1-1 DC Circuit Variables
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•
•
•
•
Resistance “R” (Ohm: Ω)
Voltage “V” (Volt: V)
Current “I” (Ampere: A)
Power “P” (Watt: W)
Energy “W” or “E” (Joules: J, or watt-hour)
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5
Comparison of DC Voltage & AC Voltage
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6
Conventional Current Flow in Opposite
Direction to Electron Flow
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7
Voltage Between Two Points in a Circuit
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8
Schematic Symbols for an Ideal Voltage
Source and a Battery
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9
Schematic Symbol for the Ideal Current
Source
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10
Schematic Symbol for a Resistance
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11
Illustration of Short Circuit &
Open Circuit
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12
Simple Circuit
Used to Illustrate Ohm’s Law
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13
Different Types of Ground
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14
Simple Circuit Redrawn with
Ground Symbols
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15
1-3 Measuring DC Circuit Variables
• Ohm-meter
• Volt-meter
• Am-meter
• Multi-meter
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16
Voltmeters are Always Connected
Between Two Points in a Circuit Across
Which the Voltage is to be Measured
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Ammeters are always Connected Within
the Branch for Which Current is to be
Measured
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1-4 Power and Energy
• Energy: work performed, or capacity to perform
work
• Power: rate of change of energy
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19
Reference Directions for Power Delivered
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Reference Directions for Power Absorbed
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1-5 Kirchoff’s Laws
• Kirchoff’s Voltage Law: algebraic sum of all
voltages in a closed loop = zero
• Kirchoff’s Current Law: algebraic sum of all
currents in a node = zero
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22
A Loop Used to Illustrate
Kirchoff’s Voltage Law
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23
Illustration of Kirchoff’s Current Law
at a Node
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24
Circuit of Example 1-8
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25
Circuit of Example 1-9
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26
1-6 Equivalent Resistance
• Series-connected resistances
• Parallel-connected resistances
• Series & parallel-connected resistances
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27
Resistances in Series and the Equivalent
Single Resistance
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28
Resistances in Parallel and the
Equivalent Single Resistance
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29
Circuit of Example 1-10
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30
Reduction of the Circuit of Example 1-10
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31
1-7 Single-Loop or Series Circuit
• One current (shared by all circuit’s components
• Multiple voltages:
– Voltage drop (across resistance)
– Voltage rise (across sources)
• Series circuit: Voltage divider
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32
Representative Single-Loop Circuit
(Series Circuit)
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33
Circuit of Example 1-11
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Circuit of Example 1-12
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1-8 Single Node-Pair or Parallel Circuit
• One voltage (drop or rise) shared by all circuit’s
components
• Multiple currents: branch currents
• Parallel circuit: Current divider
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36
Single Node-Pair (Parallel) Circuit
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Representative Parallel Circuit with
Current Sources
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Circuit of Example 1-13
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Circuit of Example 1-14
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1-9 Voltage and Current Divider Rules
• Kirchoff’s Voltage Law
• Kirchoff’s Current Law
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41
Circuit Used to Illustrate the
Voltage Divider Rule
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Circuit Used to Illustrate the Current
Divider Rule
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Circuit of Example 1-15
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Circuit of Example 1-16
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