What is the Electricity?
The invisible energy which constitutes the flow of electrons
through a circuit to do work is called electricity.
What is the Charge?
It is the smallest particles of an atom which has some property
of attraction and some property of repulsion.
What is Current?
The flow of electron is known as current or in another word rate of flow of charge is known as current
It is written by
I = dq/dt = q/t c/sec ampere (Amp)
What is the Direction of current?
In source, the current direction is from lower potential to
higher potential and in an element the current direction is from higher
potential to potential.
What is Kirchhoff’s current law?
Accordingly, the total incoming current to a junction is
equal to total outgoing current from that junction of an electric circuit or
In other word the net
current flowing at a junction of a circuit is zero.
What is the Electric Circuit?
For communicating or transferring energy from one point to
other, we require interconnection of electrical devices
An electric circuit is an interconnection of electrical
elements
Comparison of series and parallel circuit of the resistor
SERIES CIRCUIT

PARALLEL CIRCUIT

Current remains the same through all resistance

Voltage remains the same across all resistance

The voltage across each resistance is different

The current through each resistance is different

The sum of the voltages across all the resistance is the supply
voltage

The sum of the resistances is the supply current

The equivalent resistance is
R1 + R2 +………+Rn

The equivalent resistance is
1/R1 + 1/R2 +……..+1/Rn

The equivalent resistance is the largest than each of the resistances
in series

The equivalent resistance is the smallest of all the resistances in
parallel

What is the Voltage or potential difference?
Voltage is the energy required to move a unit charge through
an element.
It is denoted by ‘v’.
Its unit is volt.
1 volt = 1 joule/coulomb = 1 newton meter/coulomb
It is also known as absolute potential at the point.
What is Power?
Power is the time rate of expanding or absorbing energy
Unit of power is wattsW
P=VI
What is the Potential drop or voltage drop?
When current flows through an element the voltage produced
across that element is known as voltage drop.
Faraday’s First Law  Electromagnetic Induction
Whenever a conductor is placed in a varying magnetic field,
an EMF is induced. A current is induced when the conductor circuit is closed.
This current is named an induced current.
Faraday’s Second Law  Electromagnetic Induction
The induced electro motive force EMF in a coil is equal to
the rate of change of the flux linkage.
What is mutual induction?
When an electro motive force (EMF) is produced in a coil due
to the change in current in a coupled coil, the effect is known as mutual
inductance.
What is the Electro motive force (EMF)?
The force which motivates the electrons to flows in a circuit
known as electro motive force.
Its unit is volt.
Fleming’s right hand rule
THUMP

direction of the movement of conductor

FORE FINGER

Direction of the magnetic field

MIDDLE FINGER

Direction of the induced current

APPLICATIONS

Electric Generators

Fleming’s left hand rule
THUMP

Direction of thrust (force) on the conductor

FORE FINGER

Direction of the magnetic field

MIDDLE FINGER

Direction of the current

APPLICATIONS

Electric motors

What is Kirchoff's voltage law?
Accordingly, sum of voltages in a closed circuit on a closed path is equal to zero.
∑v=0
What is the Polarity of voltage?
The polarity of the voltage is determined with respect to the direction of flow of current.
In a source, if the current direction is from lower potential
to higher potential then the source voltage is positive.
If in a source the current direction is from higher
potential to lower potential then the source voltage is negative.
But in an element the current is always from higher potential
to lower potential, so the element voltage is negative.
What are the Application of Kirchoff's voltage law (KVL) and Kirchhoff’s current law (KCL)?
KVL and KCL are used to analyze a circuit completely i.e. to
determine each branch current, voltage, and power, etc.
During KCL we consider each and every junction point of a
circuit. The junction is a common point where 3 or more elements are joined together in a circuit.
During the application of KVL, we start from any one point of the
circuit and end at the same point.
Sign convention of power
In case of source, the power given is always positive
But in case of element power absorbed by the element is
positive but power given by the element is negative.
Circuit elements
An element is the basic building block of a circuit. There
are two types of elements
Active element
Passive element
These are the elements that activate on produces current in
a circuit.
Example
A voltage source (battery, shell)
And current source (semiconductor devices)
What is the Practical voltage source and current source?
These are the sources having some internal resistance
practically.
The internal resistance of a voltage source is connected in
series with the source but internal resistance of a current source is connected
across the source.
What is Source Conversion?
A practical voltage source can be converted to its
equivalent practical current source and vice versa.
What is the Dependent voltage source and current source?
These sources are also known as controlled sources which
depend upon other sources present in a circuit.
What is the Passive Element?
These are the receiving element on parameters which help to
carry current in a circuit.
What is the Resistor?
It is a device which opposes the flow of current.
What is the Resistance?
It is the property of a resistor by virtual of which it
opposes the flow of current.
The mathematical expression of resistance is given by ohm’s
law.
Ohm’s law
Accordingly at constant temperature and pressure the current
through a conductor is directly proportional to the voltage across the
conductor.
I ∝ V
Constructional resistance is directly proportional to
length of conductor and inversely proportional to the crosssectional area of the
conductor.
What is Resistivity?
It is defined as the total resistance offered by a conductor
per unit length.
What is the Inductor?
It is a device which opposes any change inflow of current.
What is Inductance?
It is the property of an inductor by which it opposes any change the inflow of current.
Unit of inductance is henry (H).
It is represented by L.
Symbol is
Mathematically it is given by L = NФ/I
Where
N = number of turns of the coil
Ф = Flux of the coil
I = current in the coil
What is the Inductive Reactance?
It is the property of an inductor by which it opposes the flow
of current.
It is given by; XL = 2πfL = wL
Where
f = natural frequency
w = angular frequency
What is the Node?
It is the point on point in a circuit where 2or more elements
join together.
What is the Junction?
It is a point in a circuit where 3 or more elements join
together.
Note: Each junction can be considered as a node but each
node cannot be considered as a junction.
Note 2: Nodal analysis of a circuit is based on the number of
junction
What is the Branch?
A branch is that part of the network which lies between two
junctions
What is the Loop?
A loop is any closed path of a network
What is the Mesh?
It is a loop and can’t be further divided into other loops
What is the linear circuit?
If the parameters of the circuit are independent of voltage
and current then the circuit is called linear circuit
What is the Nonlinear Circuit?
If the parameters of the circuit change with voltage and
current then the circuit is called nonlinear circuit
What is the bilateral circuit?
A circuit whose characteristics are the same in either the direction of current flow is called a bilateral circuit.
What is the Super position theorem?
Accordingly, if two or more sources are acting simultaneously
in a circuit, thencurrent in any branch is equal to the net current following
through that branch due to individual sources.
Note: During consideration of individual sources all other
sources in that circuit is considered as zero
What is the Maximum power transfer theorem?
Accordingly in an electric circuit the load resistance or
required resistance will supply maximum power only when the load resistance is
equal to the internal resistance.
What is Norton’s theorem?
Any linear bilateral circuit can be converted into an equivalent circuit consist of a current source (Isc = short circuit current) in
parallel with the equivalent resistance of the circuit across the required load
terminal.
Note: Thevenin’s circuit and Norton’s circuit are equivalent
to each other because using source conversion method Thevenin’s circuit can be
converted to Norton’s circuit and vice versa
What is the Transient Circuit?
When a circuit condition changes from ON to OFF condition
and OFF to ON condition is known as a transient circuit.
What is the Transient Time?
The time between ON to OFF condition and OFF to ON condition
is known as transient time.
AC circuit
The circuit which operates with alternating supply having some frequency with some energy stored element like inductor and capacitor
Note: DC circuit consists of resistance only but AC circuit
consists of all the three elements either in series or in parallel.
What is Power Factor?
It is the cosine angle between voltage and current of a
circuit
Power factor = cos Ф
Power factor is also defined as the ratio of resistance to the total impedance of the circuit
What is the Single Phase?
One conductor is considered a single phase
What is the Three phase?
If three conductors then considered as threephase.
In threephase AC system the phase displacement between
voltage or current of all conductors is given by 360/n = 360/3 = 120 degree
Principle of single phase AC generation
The singlephase AC generation is based on the principle of
Faraday's law of electromagnetic induction.
Accordingly when a conductor rotates within a magnetic field
and circuit and cut the magnetic flux an EMF is induced on that conductor and
is given by
E = N(dФ/dt)
Where Ф = Flux link with the conductor
N = number of turns
Lenz law
Accordingly whatever may be the cause of production the
induced EMF opposes its initial cause
What is the Form Factor?
It is the ratio of RMS value to the average value of an
alternating quantity
Vavg = 2Vm /π
VRMS = Vm/√2
Form factor = VRMS/ Vavg
1.11
What is the Crest or Peak or the amplitude factor?
It is the ratio of RMS value to maximum values of
alternating quantity
Maximum value = Vm
RMS value = Vm/√2
Peak factor = 1.414
What are the advantages of AC?
AC voltage can be raised or lowered effectively with the help of a device called transformer for different applications but it is not
easy for DC
AC machines are simple in construction and cheaper as
compared to DC
AC sources are easily available
What is the energy storing element?
Energy storing elements are inductor and capacitor
Threephase star connection
Line current IL = phase current Iph
Line voltage VL = √3 Vph
Threephase Delta connection
Line voltage VL = Vph Phase voltage
Line current IL = √3 Iph
Power
Power P = √3 VL IL
Real power = √3 VL IL cos Ф
Reactive power = √3 VL IL sin Ф
Generation
The production of electrical energy in generating stations
using renewable and nonrenewable energy sources is known as generation
What is Transmission?
The supply of generating electrical energy from generating
stations to substations are known as transmission
It is divided into two stages
Primary transmission – from generating station to Grid
Secondary transmission – from the grid to area substations
What is Distribution?
The supply of electrical energy from area substations to the consumer is known as distribution
Distribution is also divided into two types
Primary Distribution – From area substation to area
transformer
Secondary Distribution – From area transformer to consumers
What is the Apparent power (S)?
It is defined as the product of RMS value of voltage V and
current I
it is denoted by S
it is denoted by S
S = VI > VA
What is the Reactive power (Q)?
It is defined as the product of the applied voltage and the
reactive component of the current
It is also defined as an imaginary component of the apparent
power
It is represented by Q and it is measured in voltampere
reactive VAR
Q = VI sin VAR
What is the necessity and advantages of threephase systems?
 The output of the threephase machine is always greater than that of a singlephase machine of the same size. Hence for a given size and voltage, a threephase machine occupies less space and has less cost compared to a singlephase machine having the same rating
 To transmit and distribute a given amount of power a three phase system requires less copper than singlephase line
 Threephase motors have uniform torque whereas single phase motors have pulsating torques
 Singlephase motors are not selfstarting whereas three phase motors are selfstarting
 The threephase system give a steady output
 Singlephase supply can be obtained from threephase but threephase cannot be obtained from singlephase
What is the necessity of the protective device?
 In an electrical circuit, many types of faults occur which may damage the entire equipment and other devices connected to the faulty equipment’s
 Excessive high current can cause damage to equipment or to the operator
 Failure of insulation can cause severe shock to the operator
 Due to all the reasons, there is a need for various protection schemes and protective devices
What is the Fuse?
The fuse is a device which consists of a small piece of metal,
which is connected in series with the circuit. When the current through it
increases some predetermined value, the metal melts to interrupt the circuit
current which protects the circuit from excessivehigh current
What is the Fuse Element?
The part of the fuse which melts when excessive current flows
through it is called fuse element or fuse wire
What is the Rated current of fuse?
 It is that maximum current which fusing element can normally carry without any undue overheating or melting.
 It depends on
 The temperature rise of fuse contacts of the fuse holder
 Fusing element material
 Deterioration of fuse due to oxidation
What is the Fusing Current?
The minimum value of the current at which the fuse element
melts to interrupt the circuit current is called fusing current. It is always
more than the current rating of the fuse.
What is the Fusing Factor?
The ratio of minimum fusing current and the rating of the
fuse is called fusing factor. Fusing factor is always greater than one
What is the fusing elements?
Various fusing elements
Copper
Tinlead alloy
Silver
What are the Advantages of fuse?
 The simplest and cheapest form of protecting device
 Requires no maintenance
 Operation is automatic
 Minimum operating time can be made much smaller than that of circuit breaker
 Inverse timecurrent characteristic
 The capacity of clearing high values of short circuit currents
 Consistent performance
What are the Disadvantages of fuse?
 Replacement is necessary after every operation
 Replacement takes a lot of time
 They are prone to hightemperature rise
What is the necessity of earthing?
 To protect the human being from disability or death from shock in case the human body comes into contact with the frame of any electrical machinery/appliances which are electrically charged due to leakage current or fault
 To maintain the line voltage constant
What is the Magnetic Hysteresis?
The lagging of magnetic flux density (B) behind magnetic
field (H) intensity is known as magnetic hysteresis
What is the Electrical measuring instruments?
 Indicating instrument – voltmeter, ammeter
 Integrating instrument – energy meter
 Recording instrument
What are the Essential the torque of indicating instrument?
 Deflecting torque
 Controlling torque
 Damping torques
What are the types of indicating instrument?
 Moving coil type instrument
 Moving iron type instrument
 Dyna momentum type instrument
 Electrostatic instrument
 Induction instrument
What is the Luminous Flux?
It is the rate of energy radiation in the form of light
waves
Luminous flux = energy radiated/sec
Unit = Lumen
What is the Lumen?
It is defined as the candle power as the luminous flux
emitted in a unit solid angle by a source of candle power
Lumen = candle power x solid angle
What is Illumination?
It is the luminous flux received by a surface per unit area
What is the Transformer?
It is an electrostatic device which transfers electricity
from one AC circuit to another AC circuit at a constant frequency
Why transformer is an electrostatic device?
During the operation of the transformer since it remains
stationary and no rotating part, therefore, it is known as an electrostatic device.
Principle of operation of the transformer
The principle of transformer is based on Faraday's law of
mutual induction
What is the Machine?
The elements which have moving part or rotating part is known
as machine  motor
What is the Device?
The element having no rotating part is known as a device 
transformer
What is the Electromagnetic Induction?
Whenever a conductor cuts magnetic flux a dynamically
induced EMF induced in it. The magnetic of induced EMF is directly proportional
to the rate of flux linkages.
What is the Flux?
The amount of magnetic field around the magnet is represented through the lines of force is called flux. Units are webers represented by 0
What is the Flux Linkages?
The extent of interaction between flux and the conductor or
conductor and flux
What is the Difference between AC and DC?
ALTERNATING CURRENT AC

DIRECT CURRENT DC

It is the current of magnitude varying with time

It is the current of constant magnitude

It's reverse its direction while following in a circuit

It flows in one direction in the circuit

Electrons keep switching directionsforward and backward

Electrons move steadily in one direction

It is obtained from AC generator

It is obtained from a cell or battery or rectifier

The frequency of AC is 50 Hz or 60 Hz

The frequency of DC is zero

The passive parameter is the impedance

The passive parameter is the resistance only

Power factor lies between 0 to 1

Power factor is always 1

Types: sinusoidal, triangular, square

Types: pure and pulsating

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