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CHAPTER 1
BASIC ELECTRICAL CONCEPTS AND
RESISTIVE CIRCUITS
- Introduction to electric circuit
- SI Unit, Electrical Unit
- Electric Charge, Current, Voltage, Resistance and
Power
- Basic circuit elements : Active element and
Passive element
Continue…
- Ohm’s Law
- Kirchhoff Current Law (KCL) and
Kirchhoff Voltage Law (KVL)
- Series and Parallel circuit
- Voltage Divider Rule (VDR) and Current
Divider Rule (CDR)
BASIC ELECTRICAL CONCEPTS AND
RESISTIVE CIRCUITS
- Introduction to electric circuit
- SI Unit, Electrical Unit
- Electric Charge, Current, Voltage, Resistance and
Power
- Basic circuit elements : Active element and
Passive element
Introduction to Electric Circuit
Electric circuit can be defined as an
interconnection between components
or electrical devices for the purpose of
communicating or transferring energy
from one point to another. The
components of electric circuit are
always referred to as circuit elements.
BASIC ELECTRICAL CONCEPTS AND
RESISTIVE CIRCUITS
- Introduction to electric circuit
- SI Unit, Electrical Unit
- Electric Charge, Current, Voltage, Resistance and
Power
- Basic circuit elements : Active element and
Passive element
•
QUANTITY AND ELECTRICAL
UNIT
SI Unit
SI : International System of Unit that had been
introduced by National Bureau of Standards in 1964
Quantity
Basic Units
Symbol
Length
Meter
m
Mass
Kilogram
kg
Time
Second
s
Electric Current
Ampere
A
Temperature
Kelvin
K
Luminous
intensity
candela
cd
SI unit consists of decimal system that connected to the smaller or bigger
of basic unit and by using prefix for the power of tenth:
Multiplier
Prefix
Symbol
1018
Exa
E
1015
Peta
P
1012
Tera
T
109
Giga
G
106
Mega
M
103
Kilo
k
102
Hector
h
101
Deka
da
10-1
Deci
d
10-2
Centi
d
10-3
Mili
m
10-6
Micro

10-9
Nano
n
10-12
Pico
p
10-15
Femto
f
10-18
Atto
a
The derived unit commonly used in
electric circuit theory
BASIC ELECTRICAL CONCEPTS AND
RESISTIVE CIRCUITS
- Introduction to electric circuit
- SI Unit, Electrical Unit
- Electric Charge, Current, Voltage,
Resistance and Power
- Basic circuit elements : Active element and
Passive element
ELECTRIC CHARGE
•
•
•
•
Polarity: type of charge (-ve or +ve)
Electron: -ve charge
Proton: +ve charge
Electric charge create electric field of
force
Electric charge is an electrical property
of the atomic particles of which matter
consists measured in coulombs (C).
Continued…
The charge e on one electron is
negative and equal in
magnitude to 1.602  10-19 C
which is called as electronic
charge. The charges that occur
in nature are integral multiples
of the electronic charge.
ELECTRIC CHARGE
Quantity is Charge (Q)
Base Unit is Coulomb (C)
Examples of correct usage:
Charge = 10 Coulombs
Q = 10 C
CURRENT
Current is defined as the movement
of charge in a specified direction.
Electric Current Terminology
Quantity is Current (I)
Base Unit is Ampere (A)
An Ampere = Coulomb per second
Examples of usage:
Current = 10 Amperes
I = 10 A
Electric Current Relationships
Charge
Current =
Time
Q
I= t
Electric current i = dq/dt. The unit of
ampere can be derived as 1 A = 1C/s.
Examples:
Q
10 C = 2 A
I= t = 5s
TYPES OF CURRENT
i
t
Direct current (arus terus)
Alternating current
(arus ulangalik)
A direct current (dc) is a current that remains
constant with time.
An alternating current (ac) is a current that varies
sinusoidally with time. (reverse direction)
Example
A conductor has a constant current
of 5 A.
How many electrons pass a fixed
point on the conductor in one
minute?
Solution
Total no. of charges pass in 1 min is given by
5 A = (5 C/s)(60 s/min) = 300 C/min
Total no. of electronics pass in 1 min is given
300 C/min
21
 1.87 x10 electrons/ min
19
1.602 x10 C/electron
VOLTAGE
• Voltage is the electric pressure or force that
causes current.
• It is a potential energy
difference between two points.
• It is also known as an
electromotive force (emf).
Voltage Terminology
Quantity is Voltage (V)
Base Unit is Volt (V)
A Volt = Joule per second
Examples of usage:
Voltage = 20 Volts
V = 20 V
Voltage Relationships
Voltage = Energy
V= W
Q
Charge
Examples:
W
V= Q =
24 J = 6 V
4C
RESISTANCE
Resistance is the opposition
a material offers to current.
Resistance is determined by:
• Type of material (resistivity)
• Temperature of material
• Cross-sectional area
• Length of material
Resistance Terminology
Quantity is
Base Unit is
RESISTANCE (R)
OHM (W)
An ohm = Volt per ampere
Example of usage:
Resistance = 14 ohm
R = 14 Ω
Resistance Relationships
Resistivity x length
KL
Resistance =
R= A
area
Example:
1.4 x10-6 W cm x 5 x104 cm
KL
=
R=
A
2 cm2
= 5W
POWER
Power is the rate of using
energy or doing work.
Energy (W)
Work (W)
consists of a force moving
through a distance.
is the capacity to
do work.
Joule (J)
is the base unit for both energy and work.
Power Terminology
Quantity is
POWER (P)
Base Unit is WATT (W)
A watt = Joule per second
Example of usage:
Power = 200 Watts
P = 200 W
Power Relationships
Energy
Power =
Time
W
P= t
Example:
200 J = 10 W
W
P = t = 20 s
BASIC ELECTRICAL CONCEPTS AND
RESISTIVE CIRCUITS
- Introduction to electric circuit
- SI Unit, Electrical Unit
- Electric Charge, Current, Voltage, Resistance and
Power
- Basic circuit elements : Active element and
Passive element
ACTVIVE ELEMENT AND
PASSIVE ELEMENT
Active Element– elements capable of
•
•
•
•
generating electrical energy. For example:
Voltage source
Current source
Passive Element – elements are not capable of
generating electrical energy. For example:
Resistor (dissipates energy)
Capacitor and Inductor (can store or release
energy)
Independent source
This source maintains a specified
voltage between its terminals but
has no control on the current
passing through it. The symbol of
the independent voltage source is a
plus-minus sign enclosed by a
circle.
Voltage
Current
This source maintains a specified
current through its terminals but has
no control on the voltage across its
terminals. The symbol of the
independent current source is an
arrow enclosed by a circle.
Voltage
Dependent source
Current
Vs  ix
This kind of voltage source has a
specified voltage between its
terminals but it is dependable on
some other variable defined
somewhere in the circuit. The
symbol for the dependent voltage
source is a plus-minus sign
enclosed by a diamond shape.
The value of the dependent
current source is ρix (ohms)
where ρ is the scale factor or
gain.
is  Vx
This kind of current source has a
specified current between its
terminals but it is dependent on
some other variable defined
somewhere in the circuit. The
symbol for the dependent current
source is an arrow enclosed by a
diamond shape. The value of the
dependent current source is αVx (in
Siemens) where α is the scale factor
or gain.
Example
Obtain the voltage v in the branch shown
in Figure below for i2 = 1A.
Solution
Voltage v is the sum of the currentindependent 10-V source and the
current-dependent voltage source vx.
Note that the factor 15 multiplying the
control current carries the units Ω.
Therefore, v = 10 + vx = 10 + 15(1) = 25
V
Circuit symbol of resistor
Resistor
R
UNIT: Ohm (Ω)
Resistor is passive
element that dissipates
electrical energy. Linear
resistor is the resistor
that obeys Ohm’s law.
Resistor colour code
Resistor Colour Codes
Yellow
Violet
Red
Silver
4700 ±10 %
C
CAPACITOR
UNIT: Farad (F)
• Electrical component that consists of two
conductors separated by an insulator or
dielectric material.
• Its behavior based on phenomenon associated
with electric fields, which the source is voltage.
• A time-varying electric fields produce a current
flow in the space occupied by the fields.
• Capacitance is the circuit parameter which
relates the displacement current to the voltage.
A capacitor with an applied voltage
Plates – aluminum foil
Dielectric – air/ceramic/paper/mica
Plates – aluminum foil
Dielectric – air/ceramic/paper/mica
Circuit symbols for capacitors
(a) Fixed capacitor
(b) Variable capacitor
Circuit parameters
• The amount of charge stored, q = CV.
• C is capacitance in Farad, ratio of the charge on
one plate to the voltage difference between the
plates. But it does not depend on q or V but
capacitor’s physical dimensions i.e.,
A
C
d
 = permeability of
dielectric in Wb/Am
A = surface area of plates
in m2
d = distance between the
plates m
INDUCTOR
UNIT: Henry (H)
L
• Electrical component that opposes any change in
electrical current.
• Composed of a coil or wire wound around a nonmagnetic core/magnetic core.
• Its behavior based on phenomenon associated with
magnetic fields, which the source is current.
• A time-varying magnetic fields induce voltage in any
conductor linked by the fields.
• Inductance is the circuit parameter which relates the
induced voltage to the current.
Typical form of an inductor
Circuit symbols for
inductors
Air-core
iron-core
Variable
iron-core
- Ohm’s Law
- Kirchhoff Current Law (KCL) and
Kirchhoff Voltage Law (KVL)
- Series and Parallel circuit
- Voltage Divider Rule (VDR) and Current
Divider Rule (CDR)
OHM’S LAW
Georg Simon Ohm (1787-1854)
formulated the relationships among
voltage, current, and resistance as
follows:
The current in a circuit is directly
proportional to the applied voltage and
inversely proportional to the resistance
of the circuit.
V  IR
Calculating Current
Vs =
24 V
R
1.2 kW
V
24
V
= 0.02 A = 20 mA
I=
=
R
1200 W
Calculating Resistance
A
Vs =
12 V
0.02 A
R
V
12 V
R= I =
= 600 W = 0.6 k W
0.02 A
Calculating Voltage
A
Vs =
?
0.025 A
R
470 W
V = IR = 0.025 A x 470 W = 11.75 V
Calculating Power
A
V
0.25 A
67.5 V
270 W
P = IV = 0.25 A x 67.5 V = 16.9 W
P = I2R = 0.25 A x 0.25 A x 270 W = 16.9 W
P = V2/R = (67.5 V x 67.5 V) / 270 W = 16.9 W
• A branch represents a single element such as
a voltage source or a resistor.
• A node is the point of connection between
two or more branches.
• A loop is any closed path in a circuit.
• A network with b branches, n nodes, and l
independent loops will satisfy the
fundamental theorem of network topology:
b  l  n 1
Example:
Original
circuit
Equivalent circuit
How many branches, nodes
and loops are there?
- Ohm’s Law
- Kirchhoff Current Law (KCL) and
Kirchhoff Voltage Law (KVL)
- Series and Parallel circuit
- Voltage Divider Rule (VDR) and Current
Divider Rule (CDR)
KIRCHHOFF’S LAW
•
Gustav Robert Kirchhoff (1824 –
1887)
• Models relationship between:
– circuit element currents (KCL)
– circuit element voltages (KVL)
• He introduces two laws:
– Kirchhoff Current Law (KCL)
– Kirchhoff Voltage Law (KVL)
Kirchhoff ’s Current Law (KCL)
• Current entering node = current
exiting
• Convention: +i is exiting, -i is
entering
• For any circuit node:
i

0

Kirchhoff ’s Current Law (KCL)
Kirchhoff ’s Current Law (KCL) states that
the algebraic sum of current entering a
node must be equal to that of leaving the
same node.
Example
Determine the current I for the circuit
shown in the figure below.
I + 4-(-3)-2 = 0
I = -5A
We can consider
the whole
enclosed area as
one “node”.
This indicates that
the actual current
for I is flowing
in the opposite
direction.
Kirchhoff ’s Voltage Law (KVL)
• voltage increases = voltage
decreases
• Convention: hit minus (-) side
first, write negative
• For any circuit loop:
v

0

Kirchhoff ’s Voltage Law (KVL)
Kirchhoff ’s Voltage Law states that the
algebraic sum of voltage drop in a loop must
be equal to that of voltage rise in the same
loop. Stated it in a different way is that the
algebraic sum of all voltages around a loop
must be zero.
Example
• Applying the KVL equation for the circuit
of the figure below.
va-v1-vb-v2-v3 = 0
V1 = IR1 v2 = IR2
v3 = IR3
 va-vb = I(R1 + R2
+ R3)
va  vb
I
R1  R2  R3
- Ohm’s Law
- Kirchhoff Current Law (KCL) and
Kirchhoff Voltage Law (KVL)
- Series and Parallel circuit
- Voltage Divider Rule (VDR) and Current
Divider Rule (CDR)
SERIES AND PARALLEL
CIRCUIT
Resistor below is arranged in series connection:
R1
I
VS
R2
 V1 

RN
 V2 
 VN 

I
VS


Req
The equivalent resistance for any number of resistors in series
connection is the sum of each individual resistor.
Req = R1 + R2 + ……….+ RN
CURRENT IN SERIES CIRCUIT
Current in series circuit is the same as in
each circuit element.
I  I1  I 2  I N
VOLTAGE IN SERIES CIRCUIT
Voltage (VT) in series circuit is the total
voltage of each element circuit.
VT  V1  V2  ..  VN
Resistor below is arranged in parallel connection:
IS

V
I1
I2
R1
R2
IN
RN

IS

V
Req

The equivalent resistance for any number of
resistors in parallel connection is obtained by taking
the reciprocal of the sum of the reciprocal of each
single resistor in the circuit.
Equivalent resistance:
1
1
1
1


 ............ 
Req
R1 R2
RN
Req 
1
1
R1
 1
R2
 ........  1
RN
For the circuit which have two resistors in parallel
connection:
Req  R1 R2
Req 
1
1
R1
 1
R1 R2

R1  R2
R2
CURRENT IN PARALLEL CIRCUIT
• Current in series circuit is equal to
the total current for each element
circuit
I  I1  I 2  ..  I N
VOLTAGE IN PARALLEL CIRCUIT
• Voltage (VT) in series circuit is the
same as for each element circuit
VT  V1  V2  VN
- Ohm’s Law
- Kirchhoff Current Law (KCL) and
Kirchhoff Voltage Law (KVL)
- Series and Parallel circuit
- Voltage Divider Rule (VDR) and Current
Divider Rule (CDR)
VOLTAGE DIVIDER
Whenever voltage has to be divided
among resistors in series use voltage
divider rule principle.
By applying Ohm’s Law:
V2  R2 I
V
I 
R1  R2
Voltage at resistor R2:
 V 
 R2 
  V 

V2  R2 
 R1  R2 
 R1  R2 
CURRENT DIVIDER
I
V

_
I1
I2
R1
R2
Whenever current has to be divided
among resistors in parallel, use
current divider rule principle.
By applying Ohm’s Law:
 R1R2 

V  I1R1  I 2 R2  I 
R

R
 1 2
So, to find current, I1 and I2 :
 R2 
 I
I1  
R

R
2 
 1
 R1 
 I
I 2  
R

R
2 
 1