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EE111EE111
Circuit AnalysisCircuit Analysis
Slides prepared by a studentBy getting a material from net
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Lecture OutlineLecture Outline
yWhat do Electrical Engineers Do?
y Charge
y
Currenty Electrical Energy
y Electrical Power
y
Circuit Elementsy Dependent Vs Independent Sources
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What do Electrical Engineers Do?What do Electrical Engineers Do?
y Electrical Engineers design, construct,
analyze and improve electrical and
electronic components and systems in
all shapes and sizes.
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Electrical Engineering OverviewElectrical Engineering Overview
y Communication System
y Computer System
y
Control Systemy Power System
y Signal Processing System
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6Introduction
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7Introduction
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9Introduction
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Circuit Analysis Course Covers Circuit Analysis Course Covers
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Basic Circuit ElementsBasic Circuit Elements
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Relation describing behavior ofRelation describing behavior of
circuit componentscircuit components
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Problem SolvingProblem Solving
y Identify what is given and what to find
y Sketch a circuit diagram or visual model
y Think of several solution methods and
decide on a way of choosing among
them
y Calculate a solution
y Use your creativity
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International System of UnitsInternational System of Units
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Derived Units in SIDerived Units in SI
Quantity Unit Name Formula
Frequency Hertz (Hz) s-1
Force newton (N) Kg*m/s2
Energy or work joule (J) M.MPower watt (W) J/s
Electric Charge coulomb (C) A.S
Electric Potential volt (V) J/C
Electrical Resistance ohm () V/A
Electrical Conductance siemens (S) A/V
Electric Capacitance farad (F) C/V
Inductance henry (H) V*s/A
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SIPrefixesSIPrefixes
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Charge (1)Charge (1)
y Charge is an electrical property of theatomic particles of whichmatter consists,measured in coulombs (C).
y
The charge e on an electron is negative andequal in magnitude to 1.6021019 C, whilea proton carries a positive charge of thesame magnitude as the electron.
y
The presence of equal numbers of protonsand electrons leaves an atom neutrallycharged.
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Charge (2)Charge (2)
The following points should be noted about electric charge:
y The coulomb is a large unit for charges. In 1 C of charge,there are 1/(1.602 1019) = 6.24 1018 electrons. Thusrealistic or laboratory values of charges are on the orderof pC, nC, orC
y According to experimental observations, the only chargesthat occur in nature are integral multiples of theelectronic charge e = 1.602 1019 C.
y
Th
e law of conservation of charge states that charge canneitherbe created nor destroyed, only transferred. Thusthe algebraic sum of the electric charges in a system doesnot change.
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Electric CurrentElectric Current
y Electric current is the time rate of change
of charge, measured in amperes (A).
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Direct Current Vs AlternatingDirect Current Vs Alternating
CurrentCurrenty A direct current (dc) is a current that remains
constant with time.
y An alternating current (ac) is a current thatvaries sinusoidally with time.
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Examples (1)Examples (1)
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Examples (2)Examples (2)
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Examples (3)Examples (3)
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Examples (4)Examples (4)
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Voltage (1)Voltage (1)
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Voltage (2)Voltage (2)
y Voltage is the energy absorbed or expended as a unitcharge moves through a circuit element
y Analogous to pressure in hydraulic systemy Sometimes called potential differencey Can be created by a separation of chargey Is a measure of the potential between two pointsy Voltage pushes charge in one directiony We use polarity (+ and on batteries) to indicates
which direction the charge is being pushedy Voltage is the energy required to move a unit
charge through an element, measured in volts (V)
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where v= voltage in volts
w = energy in Joules
q = charge in coulombs
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Voltage (3)Voltage (3)
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Voltage (4)Voltage (4)
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Voltage (5)Voltage (5)
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y The voltage sources push current through the circuit
y The current is the rate flow of charge (i.e. electrons)
y The light bulb (resistor) resists the flow of current
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Power (1)Power (1)
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Power (2)Power (2)
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Power (3)Power (3)
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Energy (1)Energy (1)
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Example 1 (1)Example 1 (1)
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Example 1 (2)Example 1 (2)
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Example 1 (3)Example 1 (3)
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Example 2Example 2
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1.6 Circuit Elements1.6 Circuit Elements
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Kinds of SourcesKinds of Sources
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Notes on Ideal SourcesNotes on Ideal Sources
y Ideal sources are models used to simplify analysis
y These devices do not exist physically
y Ideal models serve as a good approximation of physical devices, butonly over a limited operating range
y We will use and discuss more accurate models later in the term
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