basic electrical circuits & machines (ee-107)
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Basic Electrical Circuits & Machines (EE-107). Course Teacher Shaheena Noor Assistant Professor Computer Engineering Department Sir Syed University of Engineering & Technology. VOLTAGE AND CURRENT LAWS. - PowerPoint PPT PresentationTRANSCRIPT
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Basic Electrical Circuits & Machines (EE-107)
Course TeacherShaheena Noor
Assistant ProfessorComputer Engineering Department
Sir Syed University of Engineering & Technology.
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VOLTAGE AND CURRENT LAWS
In this chapter, we discuss the behavior of electric circuits. Two simple laws, Kirchhoff’s
Current law and Kirchhoff’s voltage law form the foundation for circuit analysis
procedure.
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Voltage and Current Laws
• Circuits– Series Circuit– Parallel Circuit
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“Two components are connected in series if they have exactly one common terminal and if no other component has a terminal that shares that common connection.”
Figure (a) Figure (b)
Series Circuits
R1 R2
Common terminal
V
Commonterminal
R
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• A series path is one in which every component in the path is in series with another component.
Analysis of Series Circuit:• Important property is that the current is the same in every
series-connected component.• Another fact is its total resistance. • Total resistance is the sum of all the series-connected
resistances.
RT or Req = R1 + R2 + R3 + . . .• When a voltage source is connected in series circuit, the
total current produced by that source is from Ohm’s Law.
Series Circuits
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• Example # 01: Let R1 = 2Ω; R2 = 1 Ω; V = 5Volts; I = ?
• Example # 02: Find I and voltage across each resistor.
Series Circuits
V
R1
R2
R1 = 12 Ohm
24V
R3 = 10 Ohm
R2 = 6 Ohm
I
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It states that “ The algebraic sum of the voltages around any closed path is zero.”
V1 + V2 + V3 + . . . . . . . + VN = 0 OR• “ The sum of the voltage drops around any
closed loop equals the sum of the voltage rises around the loop.”
Kirchhoff’s Voltage Law (KVL):
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• Example 3.2Find vx and i .
Kirchhoff’s Voltage Law (KVL):
5V
+ -
7V
100 OhmV xi
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Determine i and vx for the figure given below.
Drill Problem 3.2 ( page 34)
1V
3Vi
10 OhmV x
+ -
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• Other Examples:
Kirchhoff’s Voltage Law (KVL):
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• In the circuit, vs1 = 120V, vs2 = 30V, R1 = 30Ω and R2 = 15Ω. Compute the power absorbed by each element.
Drill Problem 3.4 (page 37)
V s1
V s2R1
R2
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Drill Problem 3.5 (page 38) • In the Circuit , find the Power absorbed by each of
the five elements in the circuit.
For Dependent Sources:
7 Ohm
12 V
8 Ohm
V x30 Ohm
+ -
4Vx+-
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• Determine i in the given circuit.
Drill Problem 3.9 ( page 45)
5V
5V
5 Ohm
5V
i15 Ohm 25 Ohm
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• Break in a circuit path.• No current can flow through an open.• Since no current can flow through it, an open circuit
has an infinite resistance (R = ∞)
I = V/R = ?• Important: It is a common error that since the
current in an open circuit is zero, the voltage across the open must also be zero.
Open Circuit
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For Example:
What is the voltage ‘V’ across the switch terminal when the switch is open.
+V-
20 Ohm
60 V
40 Ohm
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Voltage Divider Rule (VDR)
R1
+ -
+ -
R2
EV1
V2
I = ?V1 = ?V2 = ?
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• Use VDR to find V200Ω and V150 Ω.
• Verify this using KVL
For Example:
36V
50 Ohm
150 Ohm
100 Ohm 200 Ohm
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• Two components are connected in parallel when they have 2 common terminal.
• For Example:
Parallel Circuits:
R3
R2R1
R2V R1R3
R1
R2
V
R2
R1
R3
R4
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Analysis of Parallel Circuits:• Important property of parallel circuit is that
every parallel-connected component has the same voltage across it.
Parallel Circuits:
R2V
R1
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• Find the current in each resistor.
For Example:
R2
4 Ohm
I3
R1
2 Ohm48V
I1
R3
6 Ohm
I2
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• Resistance in Parallel:
• For 2 resistors (only)
Parallel Circuits:
R2V
R1
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It states that: • “ The algebraic sum of the current entering
any node is zero”OR
• “The sum of all currents entering a junction or any portion of a circuit equals the sum of all currents leaving the same.”
Kirchhoff’s Current Law (KCL):
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iA iB
iD ic
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• Find the current in the 150Ω resistor
Example
330 Ohm
I3 = 0.1A
100 Ohm
270 Ohm
I4 = ?
I2 = 0.2A
150 Ohm
I1 = 0.8A
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• Find ix in each of the circuits.
Q-5 (a) (page 55)
Vix
4A 1A
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• Find ix; if iY = 2A and iZ = 0A
• Find iY; if iX = 2A and iZ = 2iYA
Q6 (page 55)
5A
3A
iZiY
iX
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• Consider 2 parallel resistor
• Note: Parallel resistors must be branches between the same pairs of nodes.
Current Division Rule (CDR):
R1
I1
R2
I2
I
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• Find I1 and I2 using the current divider rule.• Verify the result using KCL
Example:
R1 = 470 Ohm
I1
R2 = 330 Ohm
160mA
I2
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• Find current across 3Ω resistor using CDR.
Example 3.13 (Page 52)
4 Ohm
3 Ohm12V 6 Ohm
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• A short circuit is a path of zero resistance.• A component is said to be short-circuited
when there is a short circuit connected in parallel with it.
Short Circuit
R
IR = ?
I
Iss = ?