04/10/2022
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Engr. A. Janapon
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WHY DO WE NEED TO STUDY ELECTRIC
CIRCUIT THEORY?
Module 1
Module 2
ELECTRICAL CIRCUITS THEORY
Module 3
Module 4
POWER
CONTROL
COMMUNICATIONS
Module 5
Module 6
ELECTRIC MACHINES
ELECTRONICS
INSTRUMENTATION
Electrical Circuits Theory is one of the fundamental theories upon which all
branches of electrical engineering are built.
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Module 1
REVIEW OF
BASIC CONCEPTS
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Module 1
Topics:
1. Charge, Current, Voltage
2. Power and Energy
3. Resistance, Resistivity, Temperature Effects and
Power Rating of Resistor
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Topic 1
ELECTRIC CHARGE (Q)
Is a fundamental property of matter and is influenced by
elementary particles such as electrons and protons.
-1 Coulomb = 6.242 x 1018 electrons
Electron Charge = - 1.602 x 10-19 C
Proton Charge = + 1.602 x 10 -19C
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Note: Electric charge is measured by coulomb.
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ELEMENTARY PARTICLES
 Electrons – are negatively charge particles
 Protons – are positively charged particles
 Neutrons – are electrically neutral (no charge)
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Particle
Charge
Coulomb, C
Mass
Kilogram, k
Charge to
Mass Ratio
C/kg
Electron
- 1.602 x 10-19
9.109 x 10-31
1.76 x 1011
Proton
+ 1.602 x 10-19
1.673 x 10-27
3.58 x 107
Neutron
None
1.673 x 10-27
N/A
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Conservation of Charge:
The total or net electric charge in an isolated system
always remains constant.
Conservation of ChargeEnergy:
Electric Charge is neither created nor destroyed
but is transferred from one body to another.
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ELECTRIC CURRENT ( I )
Is the transfer or movement of electric charge through
the flow of electrons with respect to time.Measured in ampere (A)
Electron charge are carrying charge
Proton charge are mostly immobilize
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DID YOU KNOW?
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Andre-Marie Ampere (1775-1836), a French mathematician and physicist, defined the electric current
and developed a way to measure it in 1820s.
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Topic 1
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1. Electron moves at permi speed. Permi speed corresponds to a kinetic energy equal to permi
energy.
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2. Tiny drift velocity superimposed by the applied electric field (velocity of charge)
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FLOW OF ELECTRIC CHARGE
When a wire is connected to a battery
the charges are forced to move;
positive charges move in one
direction while negative charges
move in the opposite direction. This
motion of charges creates electric
current.
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Conventional flow was introduced by Benjamin Franklin (1706-1790), an American scientist and inventor.
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FORMULAS:
i = dq/dt
1 ampere = 1 coulomb/second
Transferred Charge Between Time:
q=
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TYPES OF CURRENT
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TYPES OF CURRENT
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Note: Oscillating Current is alternating in character. It increases and decreases in
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magnitude and changes in direction periodically.
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Topic 1
TYPES OF DIRECT CURRENT:
1. Direct/Continuous Current
transfer of energy is in a unidirectional
ex. battery
2. Unidirectional Direct Current
varies somewhat in magnitude but does not
reverse in direction
ex. dc generator
3. Pulsating Direct Current
magnitudes varies and pulsates regularly but
not reversal in direction
ex. half wave rectifier
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Topic 1
VOLTAGE ( V )
Also known as electromotive force (emf) or potential difference. It is
the energy required to move 1 coulomb of charge through an
element. Voltage is the pressure from an electrical circuit's power
source that pushes charged electrons enabling them to do work.
Measured in volts (V).
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Alessandro Antonio Volta (1745-1827), an Italian physicist, invented the electric battery. The unit of
voltage or potential difference, the volt, was named in his honor.
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FORMULAS:
v = dw/dq
1 voltage = 1 joule/coloumb
= (1 Newton.meter)/coulomb
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Topic 1
Types of Voltage:
1. DC Voltage (Direct Current Voltage)
always has the same polarity (positive or negative), such
as in battery.
2. AC Voltagec (Alternating Current Voltage)
alternates between positive and negative.
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Topic 2
POWER (P)
Is the rate, per unit time, at which electrical energy is transferred by
an electric circuit. Measured in watts (W).
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The unit watt is named after James Watt, an 18th-century Scottish Inventor.
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FORMULAS:
p = dw/dt
1 watt = 1 joule/second
Derivation:
p = vi
=
=
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NOTE:
In an electric circuit, law of conservation of energy must be obeyed.
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Topic 2
ENERGY
Is the quantitative property that must be transferred to an object in
order to perform work on, or to heat, the object. Measured in Joules
(J)
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The unit joule is named in honour of the English physicist James Prescott Joule.
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Topic 2
FORMULAS:
p = dw/dt
dw = pdt
w=
=
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NOTE:
Electric power utility measures energy in watt hours (wh), Wh = 3600 J
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Topic 3
RESISTANCE (R)
It is a property of a
substance which
opposes (or restricts)
the flow of electricity
through it. It measure
the opposition to
current flow in an
electrical circuit. It is
measured
in ohms (Ω ).
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Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship
between voltage, current and resistance.
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Topic 3
RESISTIVITY (ρ)
It is a measure of the resistance of a given size of a specific
material to electrical conduction or it is a measure of the resisting
power of a specified material to the flow of an electric current.
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LAWS OF RESISTANCE
1. It varies directly as its length.
2. It varies inversely as the cross-sectional area of the conductor.
3. It depends on the nature of the material
4. It also depends on the temperature of the conductor.
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Topic 3
FORMULA:
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remember
ρ is the resistivity or specific resistance. It is the resistance between the opposite faces
of a material.
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Topic 3
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UNITS OF RESISTIVITY
Units
Resistivity, ρ
Length, L
Area, A
S.I.
ohm-meter
meter
meter2
CGS
ohmcentimeter
centimeter
centimeter2
feet
Circular Mil
(CM)
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FORMULAS:
1 inch = 1000 mil
Circular Mil (CM) = (diameter in mil)2
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NOTE:
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Circular Mil is the unit of cross-sectional area.
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Topic 3
CONDUCTANCE (G)
The degree to which an object conducts electricity, calculated as the
ratio of the current that flows to the potential difference present. This
is the reciprocal of the resistance, and is measured in siemens (S)
or mhos (Ʊ).
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Topic 3
FORMULA:
σ - conductivity or specific conductance,
unit is siemens, earlier it is called as
mhos.
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Topic 3
EFFECT OF TEMPERATURE ON RESISTANCE
The rise of temperature:
1. Increases the resistance of pure metals.
The increase is large and fairly regular for normal ranges of
temperature.
2. Increases the resistance of alloys.
The increase is relatively small and irregular.
3. Decreases the resistance of insulators.
This is called as negative temperature-coefficient of resistance.
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NOTE:
Resistance of all wires increases as the temperature is raised.
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Topic 3
Experiment on the effect of temperature on copper:
The actual curve extends to absolute zero (-273.15ºC, or K), the
straight-line approximation which is the straight dashed line is quite
accurate for the normal operating temperature range at -234.5ºC.
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NOTE:
The temperature of -234.5ºC is called the inferred absolute temperature (Ti) of copper.
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DERIVATION OF FORMULA:
Using similar triangle on the figure:
For general use of the formula:
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NOTE:
Ti is the inferred absolute zero of a certain material.
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Topic 3
INFERRED ABSOLUTE TEMPERATURE OF CERTAIN
MATERIALS:
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Topic 3
Temperature Coefficient of Resistance, α
The resistance-change factor per degree Celsius of temperature
change . It is also the change in resistance per ohm per degree
centigrade change in temperature from the given temperature.
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NOTE:
The temperature of -234.5ºC is called the inferred absolute temperature (Ti) of copper.
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DERIVATION OF FORMULA:
From the general formula:
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DERIVATION OF FORMULA:
continuation....
where:
- is the temperature coefficient of resistance
Therefore the General Formula:
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Topic 3
POWER RATING OF RESISTOR
It is sometimes called the
Resistors Wattage Rating and
is defined as the amount of
heat that a resistive element
can dissipate for a indifinite
period of time without
degrading its performance,
becoming too hot or risking
damage to it.
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The power rating of the resitor depends on its physical size. The bigger the resistor the greater its power
rating.
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