Download Basic Electrical Circuits & Machines (EE-107)

Basic Electrical Circuits &
Machines (EE-107)
Course Teacher
Shaheena Noor
Assistant Professor
Computer Engineering Department
Sir Syed University of Engineering & Technology.
Basic Components and Electrical
Circuits
The basic goals of this chapter is to understand the
basic electrical quantities (with associated unit),
Relationship between charge, current, voltage and
power, Difference between dependent and
independent sources (both voltage and current) and
detailed knowledge of the behavior of the resistor and
Ohm’s law.
Basic Components and Electric
Circuits
• Components
• Electric Circuits
Charge, Current, Voltage and Power
Charge:
• Definition  It is define in terms of ampere by
counting the total charge that passes through
a wire in one second.
• Symbol  Q or q
• Unit of Measurement  Coulomb
• Unit Abbreviated  C
Charge, Current, Voltage and Power
Current:
• Definition  Transfer of charge OR transfer
energy from one point to another.
• For Example  Power transmission line
(practical example of transfer energy)
Charge, Current, Voltage and Power
• It has numerical value and direction.
• Correct Representation  i (t)
• Two methods of representation for the exact
same current.
1
- 3A
3A
Figure a
Figure b
• Improper/incomplete definitions of a current
i1(t)
Charge, Current, Voltage and Power
• Symbol  I or i
• Unit of Measurement  Ampere (“Amp”)
• Unit Abbreviated  A
Charge, Current, Voltage and Power
Types of Current:
o A current that is constant in time is termed as
Direct Current or simply dc.
i
t
Charge, Current, Voltage and Power
Types of Current:
o Current that vary sinusoidally with time;
current of this form are present in normal
household circuits. Such a current is often
referred to as Alternating current or ac.
i
t
Charge, Current, Voltage and Power
Types of Current:
o Exponential Currents & Damped Sinusoidal
current (will discuss later)
i
i
t
t
Drill Problem 2.3 (page 11)
• In the wire of the given figure, electrons are
moving left to right to create a current of
1mA. Determine I1 and I2.
I1
I2
Charge, Current, Voltage and Power
Voltage:
• Consider an object with 2 terminals.
A
B
A general 2terminal
circuit
element
• Two paths by which current may enter or
leave the element.
Charge, Current, Voltage and Power
• Symbol  V or v or E
• Unit of Measurement  “Volts”
• Unit Abbreviated  V
Charge, Current, Voltage and Power
• Inadequate definitions of a voltage
+
V1(t)
-
• A correct definition
+
V1(t)
-
A correct definition
includes both a symbol
for the variable and a
plus-minus symbol pair.
Charge, Current, Voltage and Power
• Voltage:
A
A
+
-
V = -5V
V = 5V
-
+
B
B
Fig (a)
A
Fig (b)
A
+
-
V = 5V
V = -5V
-
+
B
B
Fig (c)
FigFig(d)(d)
Charge, Current, Voltage and Power
Important Point:
• A voltage can exist between a pair of electrical
terminals whether a current is flowing or not.
• For example  An automobile battery has a
voltage of 12V across its terminals even if
nothing is connected to the terminals.
Drill Problem 2.4 (page 13)
• For the given figure; if V1 = 17V. Determine V2.
+
V1
-
-
V2
+
Charge, Current, Voltage and Power
Power:
• Definition Power is a measure of how much work
can be performed in a given amount of time.
• In electric circuits, power is a function of both voltage
and current.
P = VI
• Symbol  P or p
• Unit of Measurement  Watt
• Unit Abbreviated  W
Drill Problem 2.5 (page 15)
Find the power being absorbed by the circuit element.
+
220mV
4.6A
-
Drill Problem 2.6 (page 15)
• Find the power being generated by the circuit
element.
+
-3.8V
-
-1.75A
Drill Problem 2.7 (page 15)
• Find the power being delivered by the circuit
element at t = 5ms.
8e-100t V
+
-
3.2A
Voltage and Current Sources
• Independent Source
• Dependent Source
Voltage and Current Sources
Independent Voltage Source
Vs
+
-
Voltage and Current Sources
Independent Voltage Source
• Other Representations
Vs
Battery Symbol
+
-
Ac voltage source
Voltage and Current Sources
• Independent Current Source
Is
Voltage and Current Sources
Dependent Sources
• Also referred as controlled source.
• It is determined by a voltage or current
existing at some other location in the system
being analyzed.
• Symbol  A diamond Shape
Voltage and Current Sources
• Four Different types of Dependent Sources
Kix
Figure (a)
gVx
+
KVx -
Figure (b)
Figure (c)
+
rix
Figure (d)
Drill Problem 2.8 (page 18)
• Find the power absorbed by each element in
the circuit given below.
- -Vx +
5A
+
8V
+ - 12V +
+
8V
12 V
-
-
+
0.25Vx
20 V
7A
-
2A
8A
-
Ohm’s Law
• The voltage across conducting materials is
directly proportional to the current flowing
through the material.
V=I*R
• Power: P = V * I
• Power Absorption:
Drill Problem 2.9, 2.10 (Page 23)
• With reference to V and I defined in the given
figure, compute the following quantities.
figure
2.9: R if I = -1.6mA and V = -6.3V
2.10: The absorbed power if V = -6.3V and R = 21Ω