sinusoidal signals & phasors sinusoidal signals & phasors dr. mohamed refky amin electronics...
TRANSCRIPT
Sinusoidal Signals & Phasors
Dr. Mohamed Refky Amin
Electronics and Electrical Communications Engineering Department (EECE)
Cairo University
http://scholar.cu.edu.eg/refky/
OUTLINE
โข Previously on ELCN102
โข AC Circuits
โข Sinusoidal Signals
โข Phasor Representation
Dr. Mohamed Refky 2
Previously on ELCN102
Dr. Mohamed Refky
CapacitorsWhen a voltage source is connected to a capacitor, an electric
field is generated in the dielectric and charges are accumulated on
the plates.
๐ = ๐ถ ร ๐
๐ถ =๐
๐
The amount of charge (๐) that a capacitor can store per volt
across the plates, is its capacitance (๐ถ).
Coulomb Farad
Volt
3
Previously on ELCN102
Dr. Mohamed Refky
Series and Parallel Combinations
Series Capacitors
1
๐ถ๐๐=
1
๐ถ1+
1
๐ถ2+โฏ+
1
๐ถ๐
๐ = ๐ถ ร ๐
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Previously on ELCN102
Dr. Mohamed Refky
Series and Parallel Combinations
Parallel Capacitors ๐ = ๐ถ ร ๐
๐ถ๐๐ = ๐ถ1 + ๐ถ2 +โฏ+ ๐ถ๐
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Previously on ELCN102
Dr. Mohamed Refky
InductorsWhen the current flowing through an
inductor changes, the magnetic field induces
a voltage in the conductor, according to
Faradayโs law of electromagnetic induction,
to resist this change in the current.
๐ฃ๐ฟ ๐ก = ๐ฟ๐๐๐ฟ ๐ก
๐๐ก
๐ฟ is the inductance in Henri (๐ป)
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Previously on ELCN102
Dr. Mohamed Refky
Series and Parallel Combinations
Series Inductors
๐ฟ๐๐ = ๐ฟ1 + ๐ฟ2 +โฏ+ ๐ฟ๐
7
Previously on ELCN102
Dr. Mohamed Refky
Series and Parallel Combinations
Parallel Inductors
1
๐ฟ๐๐=
1
๐ฟ1+
1
๐ฟ2+โฏ+
1
๐ฟ๐
8
Previously on ELCN102
Dr. Mohamed Refky
Transient AnalysisThe transient response of the circuit is the response when the input
is change suddenly or a switches status change.
๐ฃ ๐ก =
๐ฃ1 ๐ก , ๐ก0 < ๐ก < ๐ก1๐ฃ2 ๐ก , ๐ก1 < ๐ก < ๐ก2
โฎ๐ฃ๐ ๐ก , ๐ก๐โ1 < ๐ก < ๐ก๐
๐ฃ ๐ก the same
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Previously on ELCN102
Dr. Mohamed Refky
Steady State AnalysisThe steady state response of the circuit is the response when the
status of the circuit does not change for long time.
๐ฃ ๐ก the same
10
Previously on ELCN102
Dr. Mohamed Refky
Time Domain Analysis 1st Order Systems
๐๐ and ๐๐ are the initial and final capacitor voltages, respectively.
๐ = ๐ ๐๐๐ถ, ๐ ๐๐ is the resistance seen between the capacitor nodes
while all sources are switched off.
๐ฃ๐ ๐ก = ๐๐ โ ๐๐ โ ๐๐ ๐โ๐ก๐
RC Circuits
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Previously on ELCN102
Dr. Mohamed Refky
Time Domain Analysis 1st Order Systems
๐ผ๐ and ๐ผ๐ are the initial and final inductor current, respectively.
๐ = ๐ฟ/๐ ๐๐, ๐ ๐๐ is the resistance seen between the inductor nodes
while all sources are switched off.
๐๐ฟ ๐ก = ๐ผ๐ โ ๐ผ๐ โ ๐ผ๐ ๐โ๐ก๐
RL Circuits
12
Previously on ELCN102
Dr. Mohamed Refky
AC CircuitsAn AC circuit is a combination of active elements (Voltage and
current sources) and passive elements (resistors, capacitors and
coils).
Unlike resistance, capacitors and coils can store energy and do
not dissipate it. Thus, capacitors and coils are called storage
elements.13
Previously on ELCN102
Dr. Mohamed Refky
AC CircuitsAn AC circuit is a combination of active elements (Voltage and
current sources) and passive elements (resistors, capacitors and
coils).
The sources are usually AC sinusoidal voltage or current sources
14
Sinusoidal Signals
Dr. Mohamed Refky
DefinitionA sinusoid is a signal that has the form of the sine or cosine
function.
๐๐ด๐ถ = ๐๐ sin ๐๐ก ๐๐ = 2๐ โ ๐ =2๐
๐
amplitude
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Sinusoidal Signals
Dr. Mohamed Refky
DefinitionA sinusoid is a signal that has the form of the sine or cosine
function.
โข ๐๐ is the amplitude of the sinusoid
โข ๐ is the angular frequency in rad/s
โข ๐๐ก is the argument of the sinusoid
โข ๐ =๐
2๐is the sinusoid frequency
โข ๐ =1
๐is the sinusoid period
๐๐ด๐ถ = ๐๐ sin ๐๐ก ๐๐ = 2๐ โ ๐ =2๐
๐
16
Sinusoidal Signals
Dr. Mohamed Refky
Why Do We Study Sinusoidal Signals?We study the sinusoid because:
โข A sinusoidal signal is easy to generate and transmit. It is the
form of voltage generated throughout the world and supplied
to homes, factories, laboratories.
โข Through Fourier analysis, any practical periodic signal can be
represented by a sum of sinusoids.
โข A sinusoid is easy to handle mathematically. The derivative
and integral of a sinusoid are themselves sinusoids.
โข For a linear time invariant system (LTI), a sinusoid is an eigen
function to the system.
17
Sinusoidal Signals
Dr. Mohamed Refky
Eigen function of an LTI system
If ๐ฅ ๐ก is an Eigen function to an LTI system, the response of the
system to the input ๐ฅ ๐ก is
๐ฆ ๐ก = ๐ผ๐ฅ ๐ก
๐ผ is generally complex number causing a change in both the
magnitude and phase.
18
Sinusoidal Signals
Dr. Mohamed Refky
Phase shift
๐๐ด๐ถ = ๐๐ sin ๐๐ก๐๐ด๐ถ = ๐๐ sin ๐๐ก + ๐๐๐ด๐ถ = ๐๐ sin ๐๐ก โ ๐
The phase shift is positive if the signal is shifted to the left and isnegative if the signal is shifted to the right.
19
Sinusoidal Signals
Dr. Mohamed Refky
Complex NumbersA complex number can be written in two forms: rectangular
form and polar form.
The rectangular form consists of a
real part and an imaginary part.
๐ = ๐ฅ + ๐๐ฆ
The polar form consists of a
magnitude and phase.
๐ = ๐๐๐๐ = ๐โ ๐
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Sinusoidal Signals
Dr. Mohamed Refky
Complex NumbersA complex number can be written in two forms: rectangular
form and polar form.
To convert from rectangular form
to polar form
๐ = ๐ฅ2 + ๐ฆ2,
To convert from polar form to
rectangular form
๐ฅ = ๐ cos ๐ , ๐ฆ = ๐ sin ๐
๐ = tanโ1๐ฆ
๐ฅ
21
Sinusoidal Signals
Dr. Mohamed Refky
Complex NumbersA complex number can be written in two forms: rectangular
form and polar form.
Complex numbers are added/subtracted easily in rectangular
form
๐1 = ๐ฅ1 + ๐๐ฆ1, ๐2 = ๐ฅ2 + ๐๐ฆ2
Then
๐1 + ๐2 = ๐ฅ1 + ๐ฅ2 + ๐ ๐ฆ1 + ๐ฆ2
๐1 โ ๐2 = ๐ฅ1 โ ๐ฅ2 + ๐ ๐ฆ1 โ ๐ฆ2
22
Sinusoidal Signals
Dr. Mohamed Refky
Complex NumbersA complex number can be written in two forms: rectangular
form and polar form.
Complex numbers are multiplied/divided easily in polar form
๐1 = ๐1๐๐๐1 = ๐1โ ๐1, ๐2 = ๐2๐
๐๐2 = ๐2โ ๐2
Then
๐1 ร ๐2 = ๐1 ร ๐2 ๐๐ ๐1+๐2 = ๐1 ร ๐2 โ ๐1 + ๐2
๐1/๐2 = ๐1/๐2 ๐๐ ๐1โ๐2 = ๐1/๐2 โ ๐1 โ ๐2
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Phasor Representation
Dr. Mohamed Refky
Definition
The locus of ๐๐๐ is a circle with radius 1.
๐๐๐
๐ = 0๐๐ = 30๐๐ = 60๐๐ = 135๐๐ = 225๐๐ = 315๐ ๐ = โ45๐
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Phasor Representation
Dr. Mohamed Refky
Definition
sin ๐
๐๐๐ = cos ๐ + ๐ sin ๐
cos ๐ = ๐ ๐ ๐๐๐
sin ๐ = ๐ผ๐ ๐๐๐
Eulerโs identity
cos ๐
๐๐๐
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Phasor Representation
Dr. Mohamed Refky
DefinitionThe sinusoid function ๐ฃ ๐ก = ๐๐ cos ๐๐ก + ๐ can be written as
๐ฃ ๐ก = ๐ ๐ ๐๐๐๐ ๐๐ก+๐
= ๐ ๐ ๐๐๐๐ ๐ ๐๐ ๐๐ก
= ๐ ๐ ๐๐๐ ๐๐ก
๐ = ๐๐๐๐ ๐ = ๐๐โ ๐
๐๐๐๐ ๐ is the phasor representation of ๐๐ cos ๐๐ก + ๐
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Phasor Representation
Dr. Mohamed Refky
DefinitionA sinusoid
๐ฃ ๐ก = ๐๐ cos ๐๐ก + ๐
= ๐ ๐ ( ๐๐๐๐๐ก)
can be represented by the projection,
on the horizontal axis, of a phasor
rotating with a constant angular
velocity ๐.
๐ = ๐๐โ ๐
๐๐ is the circle radius
โ ๐ is the initial phasor position27
Phasor Representation
Dr. Mohamed Refky
DefinitionA sinusoid
๐ฃ ๐ก = ๐๐ sin ๐๐ก + ๐
= ๐ผ๐ ( ๐๐๐๐๐ก)
can be represented by the projection, on the vertical axis, of a
phasor rotating with a constant angular velocity ๐.
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Phasor Representation
Dr. Mohamed Refky
Phasors
The cosine function leads the sine function by 90๐
cos ๐๐ก = sin ๐๐ก + 90๐
sin ๐๐ก = cos ๐๐ก โ 90๐
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Phasor Representation
Dr. Mohamed Refky
Graphical approachThe cosine function leads the sinefunction by 90๐
cos ๐๐ก = sin ๐๐ก + 90๐
sin ๐๐ก = cos ๐๐ก โ 90๐
Graphical approach is very handyin representing the addition oftwo sinusoids of the samefrequency
๐ = ๐ผ cos ๐๐ก + ๐ฝ sin ๐๐ก
= ๐พ cos ๐๐ก โ ๐ ๐พ = ๐ผ2 + ๐ฝ2, ๐ = tanโ1๐ฝ
๐ผ30
Phasor Representation
Dr. Mohamed Refky
Sinusoid-Phasors transformation
Phasor domain is also known as the frequency domain.
Time-domain representation Phasor representation
๐๐ cos ๐๐ก + ๐ ๐๐โ ๐
๐๐ sin ๐๐ก + ๐ ๐๐โ ๐ โ 90๐
๐ผ๐ cos ๐๐ก + ๐ ๐ผ๐โ ๐
๐ผ๐ sin ๐๐ก + ๐ ๐ผ๐โ ๐ โ 90๐
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Phasor Representation
Dr. Mohamed Refky
Example (1)For the sinusoid 5sin(4๐๐ก + 60๐) calculate its amplitude, phase,
angular frequency, frequency, and period.
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Phasor Representation
Dr. Mohamed Refky
Example (2)Transform these sinusoids to phasors representation:
๐ฃ = 6cos(50๐ก โ 40๐)
๐ = โ4 sin(50 ๐ก + 50๐)
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Phasor Representation
Dr. Mohamed Refky
Example (3)Transform these phasors representation to sinusoids:
๐ = 8๐โ๐20๐
๐ = 3 + ๐4
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Phasor Representation
Dr. Mohamed Refky
Example (4)Calculate the phase angle (phase difference) between:
๐ฃ1 = โ10cos(๐๐ก + 50๐) ๐๐๐ ๐ฃ2 = 12 sin(๐๐ก โ 10๐)
State which sinusoid is leading.
35
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
If the current in a resistor ๐ is given by:
๐๐ ๐ก = ๐ผ๐cos(๐๐ก)
The resistor voltage will be given by
๐ฃ๐ ๐ก = ๐ ร ๐๐ ๐ก = ๐ ๐ผ๐ cos ๐๐ก = ๐๐cos(๐๐ก)
๐ผ = ๐ผ๐โ 0๐ ๐ = ๐๐โ 0
๐ = ๐ ๐ผ๐โ 0๐
Resistor
For a resistor, the voltage and current are in phase
36
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
If the current in an inductor ๐ฟ is given by:
๐๐ฟ ๐ก = ๐ผ๐ฟcos(๐๐ก)
The inductor voltage will be given by
๐ฃ๐ฟ ๐ก = ๐ฟ๐๐๐ฟ ๐ก
๐๐ก= โ๐๐ฟ๐ผ๐ฟ sin ๐๐ก = โ๐๐ฟ sin(๐๐ก)
๐ผ = ๐ผ๐โ 0๐ ๐ = ๐๐ฟโ 90
๐ = ๐๐ฟ๐ผ๐ฟโ 90๐
Inductor
For an inductor, the current lags the voltage by 90๐
37
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
If the voltage in a capacitor ๐ถ is given by:
๐ฃ๐ถ ๐ก = ๐๐ถcos(๐๐ก)
The capacitor current will be given by
๐๐ถ ๐ก = ๐ถ๐๐ฃ๐ถ ๐ก
๐๐ก= โ๐๐ถ๐๐ถ sin ๐๐ก = โ๐ผ๐ถ sin(๐๐ก)
๐ = ๐๐ถโ 0๐ ๐ผ = ๐ผ๐ถโ 90
๐ = ๐๐ถ๐๐ถโ 90๐
Capacitor
For an capacitor, the current leads the voltage by 90๐
38
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
๐ผ = ๐ผ๐โ 0๐ ๐ = ๐ ๐ผ๐โ 0
๐
๐ = ๐๐โ 0๐ ๐ผ = ๐ถ๐๐๐โ 90
๐๐ผ = ๐ผ๐โ 0๐ ๐ = ๐ฟ๐๐ผ๐โ 90
๐
inductor capacitor
resistor
39
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
The impedance ๐ of a circuit is the ratio of the phasor voltage ๐to the phasor current ๐ผ, measured in ฮฉ.
Resistor Inductor Capacitor
๐ฃ๐ ๐ก = ๐ ๐๐ ๐ก ๐ฃ๐ฟ ๐ก = ๐ฟ๐๐๐ฟ ๐ก
๐๐ก๐๐ถ ๐ก = ๐ถ
๐๐ฃ๐ถ ๐ก
๐๐ก
๐๐ = ๐ ร ๐ผ๐ ๐๐ฟ = ๐๐ฟ๐ผ๐ฟโ 90
๐
= ๐๐ฟ๐ ร ๐ผ๐ฟ
๐ผ๐ถ = ๐๐ถ๐๐ถโ 90๐
= ๐๐๐ถ ร ๐๐ถ
๐๐ = ๐ ๐๐ฟ = ๐๐L ๐๐ถ =1
๐๐๐ถ= โ
๐
๐๐ถ
40
Phasor Representation
Dr. Mohamed Refky
Phasor Relationships for Circuit Elements
The admittance ๐ of a circuit is the ratio of the phasor current ๐ผto the phasor voltage ๐, measured in ฮฉโ1.
Resistor Inductor Capacitor
๐ฃ๐ ๐ก = ๐ ๐๐ ๐ก ๐ฃ๐ฟ ๐ก = ๐ฟ๐๐๐ฟ ๐ก
๐๐ก๐๐ถ ๐ก = ๐ถ
๐๐ฃ๐ถ ๐ก
๐๐ก
๐๐ = ๐ ร ๐ผ๐ ๐๐ฟ = ๐๐ฟ๐ผ๐ฟโ 90
๐
= ๐๐ฟ๐ ร ๐ผ๐ฟ
๐ผ๐ถ = ๐๐ถ๐๐ถโ 90๐
= ๐๐๐ถ ร ๐๐ถ
๐๐ =1
๐ ๐๐ฟ =
1
๐๐L= โ
๐
๐L๐๐ถ = ๐๐๐ถ
41
Phasor Representation
Dr. Mohamed Refky
Impedance and Admittance
The impedance ๐ of a circuit is the ratio of the phasor voltage ๐to the phasor current ๐ผ, measured in ฮฉ.
๐ = ๐ + ๐๐
๐ is the resistance & ๐ is the reactance
๐ is inductive if ๐ is +๐ฃ๐.
๐ is capacitive if ๐ is โ๐ฃ๐.
๐, ๐ , and ๐ are in units of ฮฉ
Impedance
๐๐ฟ = ๐๐L
๐๐ถ =1
๐๐๐ถ= โ
๐
๐๐ถ
42
Phasor Representation
Dr. Mohamed Refky
Impedance and Admittance
The admittance ๐ of a circuit is the ratio of the phasor current ๐ผ to
the phasor voltage ๐, measured in ฮฉโ1.
๐ = ๐บ + ๐๐ต
๐บ is the conductance & ๐ต is the susceptance.
๐ is inductive if ๐ต is โ๐ฃ๐.
๐ is capacitive if ๐ต is +๐ฃ๐.
๐, ๐บ, and ๐ต are in units of ฮฉโ1
Admittance
๐๐ฟ =1
๐๐L= โ
๐
๐L
๐๐ถ = ๐๐๐ถ
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Phasor Representation
Dr. Mohamed Refky
Impedance Combination
๐๐๐ = ๐1 + ๐2 +โฏ+ ๐๐
๐ผ ร ๐๐๐ = ๐ผ ร ๐1 + ๐ผ ร ๐2 +โฏ+ ๐ผ ร ๐๐
๐๐๐ = ๐1 + ๐2 +โฏ+ ๐๐
Series Combination
44
Phasor Representation
Dr. Mohamed Refky
Impedance Combination
๐ผ๐๐ = ๐ผ1 + ๐ผ2 +โฏ+ ๐ผ๐
๐
๐๐๐=
๐
๐1+๐
๐2+โฏ+
๐
๐๐
Parallel Combination
45
Phasor Representation
Dr. Mohamed Refky
Impedance Combination
1
๐๐๐=
1
๐1+
1
๐2+โฏ+
1
๐๐
Parallel Combination
46
Phasor Representation
Dr. Mohamed Refky
Admittance Combination
๐๐๐ = ๐1 + ๐2 +โฏ+ ๐๐
๐ผ
๐๐๐=
๐ผ
๐1+
๐ผ
๐2+โฏ+
๐ผ
๐๐
Series Combination
47
Phasor Representation
Dr. Mohamed Refky
Admittance Combination
1
๐๐๐=
1
๐1+1
๐2+โฏ+
1
๐๐
Series Combination
48
Phasor Representation
Dr. Mohamed Refky
Admittance Combination
๐ผ๐๐ = ๐ผ1 + ๐ผ2 +โฏ+ ๐ผ๐
๐ ร ๐๐๐ = ๐ ร ๐1 + ๐ ร ๐2 +โฏ+ ๐ ร ๐๐
๐๐๐ = ๐1 + ๐2 +โฏ+ ๐๐
Parallel Combination
49
Phasor Representation
Dr. Mohamed Refky
Voltage DividerWhen impedances are connected in series, the total voltage
across these impedances is divided between them with a ratio that
depends on the values of theses impedance.
๐๐๐ = ๐ผ ร ๐1 + ๐ผ ร ๐2
= ๐ผ ๐1 + ๐2
๐ผ =๐๐๐
๐1 + ๐2
50
Phasor Representation
Dr. Mohamed Refky
Voltage DividerWhen impedances are connected in series, the total voltage
across these impedances is divided between them with a ratio that
depends on the values of theses impedance.
๐๐1 = ๐ผ ร ๐1 = ๐๐๐๐1
๐1 + ๐2= ๐๐๐
๐1๐๐๐
๐๐2 = ๐ผ ร ๐2 = ๐๐๐๐2
๐1 + ๐2= ๐๐๐
๐2๐๐๐
51
Phasor Representation
Dr. Mohamed Refky
Current DividerWhen impedances are connected in parallel, the total current is
divide between these impedances with a ratio that depends on the
values of theses impedances.
๐ผ = ๐ผ1 + ๐ผ2 =๐
๐1+๐
๐2
= ๐๐1 + ๐2๐1๐2
๐ = ๐ผ๐1๐2
๐1 + ๐2
52
Phasor Representation
Dr. Mohamed Refky
Current DividerWhen impedances are connected in parallel, the total current is
divide between these impedances with a ratio that depends on the
values of theses impedances.
๐ผ1 =๐
๐1= ๐ผ
๐2๐1 + ๐2
= ๐ผ๐๐๐๐1
๐ผ2 =๐ผ
๐2= ๐ผ
๐1๐1 + ๐2
= ๐ผ๐๐๐๐2
๐๐๐ =๐1๐2
๐1 + ๐253
Phasor Representation
Dr. Mohamed Refky
Star-Delta Transformation
๐๐ด๐ต = ๐๐ด + ๐๐ต +๐๐ด๐๐ต๐๐ถ
๐๐ด๐ถ = ๐๐ด + ๐๐ถ +๐๐ด๐๐ถ๐๐ต
๐๐ต๐ถ = ๐๐ต + ๐๐ถ +๐๐ต๐๐ถ๐๐ด
๐๐ด =๐๐ด๐ต๐๐ด๐ถ
๐๐ด๐ถ + ๐๐ต๐ถ + ๐๐ด๐ต๐๐ถ =
๐๐ต๐ถ๐๐ด๐ถ๐๐ด๐ถ + ๐๐ต๐ถ + ๐๐ด๐ต
๐๐ต =๐๐ด๐ต๐๐ต๐ถ
๐๐ด๐ถ + ๐๐ต๐ถ + ๐๐ด๐ต
54
Phasor Representation
Dr. Mohamed Refky
Example (5)Find the equivalent impedance of the shown circuit. Assume ๐= 50 ๐๐๐/๐ .
55
Phasor Representation
Dr. Mohamed Refky
Example (6)Find the current ๐ผ for the circuit shown
56
Phasor Representation
Dr. Mohamed Refky
Example (7)Find the current ๐ผ for the circuit shown
57
Phasor Representation
Dr. Mohamed Refky
Example (8)For the circuit shown,
๐ = 5๐ฮฉ, ๐ถ = 0.1๐๐น and ๐ฃ๐๐ ๐ก = 10 cos(4000๐ก)find the circuit current ๐ ๐ก and the capacitor voltage ๐ฃ๐ ๐ก .
58
Phasor Representation
Dr. Mohamed Refky
Example (9)For the circuit shown,
๐ = 4ฮฉ, ๐ฟ = 0.2๐ป and ๐ฃ๐๐ ๐ก = 5 ๐ ๐๐(10๐ก)find the circuit current and the inductor voltage.
59