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Basic Electrical Engineering

15ELE15/25

BASIC ELECTRICAL ENGINEERING :
MODULE - 1
I
...


Ohm's law : " The potential difference between the two ends of a conductor is directly
proportional to the current flowing through it, provided its temperature & other
parameters remain unchanged "
...
Their v-i relationship
is given by ,
[ V= K Im ] - Here the relation between V & I is non linear
...

- It is not applicable to 'arc lamps', because arc produced exhibits non-linear characteristics
...
Kirchhoff's current law [ KCL ] " Algebraic sum of all currents meeting at a node is zero in any electric circuit"
OR
" Sum of all currents entering a node is equal to sum of all currents leaving a node in any
electrical circuit
...


II
...
"
or
" In any electrical network, the algebraic sum of voltage drops of all branches and emf's
forming a closed loop is zero
...
(1)

as per KCL

I = I1 + ( I1R1 / R2 )


...
ELECTROMAGNETISM & ELECTROMAGNETIC INDUCTION :
Syllabus : Review of field around a conductor & coil, magnetic flux & flux density, mmf ,
magnetic field intensity, reluctance & permeability, definition of magnetic circuit
& analogy between electric & magnetic circuit
...
Self inductance, mutual
inductance and coefficient of coupling
...
Force on
current carrying conductor placed in a magnetic field, Fleming's left hand rule
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Magnetic field :The space around a magnet in which the magnetic effects are felt is known as magnetic
field
...
Magnetic flux :- [Ø]
The magnetic lines of force originate from north pole N & go into south pole S
...
It is expressed in
[WB]
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3
...
It is
expressed in (Wb/m2) or Tesla (T)
...
Magneto motive force (mmf) :mmf is the force that drives flux through a magnetic circuit
...
It is analogous to emf
...


5
...
Reluctance:Opposition offered to the production of magnetic flux
...

It is expressed in (AT/Wb)
It is analogous to resistance
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Permeability:It is the property of a magnetic material by virtue of which magnetic flux can be easily
created in it
...


a) Absolute permeability (µ)
b) Relative permeability (µr)

[µ = B / H]
[µr = B / B0] B0 - flux induced in free space

8
...

Mean circumference of the ring is taken as length of magnetic circuit
...
mmf creates magnetic flux
...
Reluctance is opposition offered
magnetic flux
...
Magnetic flux Ø (Wb)

Electric Current I, (A)

4
...
Permeance, G (Wb/A)

Conductance, G (S)

6
...
Magnetic field intensity H (At/m)

Electric field intensity E (V/m)

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

Differences Between Magnetic Circuit And Electric Circuit

Magnetic circuit

Electric circuit

1
...


Energy must be continuously
supplied to maintain current flow
...
It stores energy

It dissipates energy in the form of
heat
...
Saturation exists in magnetic circuits
( B
...


ELECTROMAGNETIC INDUCTION :
Faraday's laws of electromagnetic induction I law :- Whenever magnetic flux linking a coil changes, emf is induced
...


Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

II law:- The magnitude of induced emf is equal to rate of change of flux linking the coil
...

dØ/dt
e e==- -NNdØ
/ dt

Property of electromagnetism :
" Every current carrying conductor produces its own flux around it "
...


Right hand thumb rule :
When a conductor is held in the palm - Thumb points towards direction of current
Curled fingers represent direction of flux

Types of induced emf :
1
...

Example - Generators

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

2
...
(flux and conductor remain
stationary)
a) Self induced emf - Current is passed through a coil, flux develops around it
...

b) Mutually induced emf - Emf induced when varying flux in a coil links with the
neighbouring coil and induces emf in neighbouring coil
...

Or
When current is increased through a coil, it is opposed by instantaneous production of emf
(self induced / counter emf) or when current is decreased , it is also opposed by self induced
emf [delayed]
...

Self inductance is measured in terms of co efficient of self induction
...

Work done to overcome the opposition due to induced emf for an increase in current is given
by
Total energy W absorbed is given byW=

ʃe i dt = ʃL (di/dt) i dt = ʃLi di = L i / 2 = (1/2) LI
2

2

Mutual inductance :
The ability of a coil to induce emf in the neighbouring coil by induction due to change in
current in 1st coil
...

Let V1 be the applied voltage in coil1
...
emf induced in coil 2 is given
by ,
e12 = - N2 dØ12/dt

e12 = - N2 (dØ12/di1) X (di1/dt)

e12 = - M12 di1/dt

where M12 is the mutual inductance given by ,

M12 = N2 dØ12/di1

Coefficient Of Coupling :- [ Relation between L1 , L2 & M ]
It is a measure of proximity between two coils
...

Consider two magnetically coupled coils A & B with turns N1 & N2
...
c
...
c
...
"
Direction given by Flemings left hand rule
Thumb represents direction of motion (force)
forefinger represents direction of flux
second finger represents direction of current carrying
conductor

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

QUESTION BANK :
1(a) D
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State and explain Kirchhoff’s laws as applied to DC Circuits
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What are the advantages of parallel circuit over series circuit?(Jan 2010,5M)
3
...
(Jan 2013,6M)
4
...
The total power dissipation in the circuit is 70W when the applied
voltage is 20V
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(June 2014,6M)
5
...
Find the value
of R & the total current
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Obtain the potential difference Vxy in the circuit shown in figure (b)
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Find the currents in all the resistors of the network shown in the figure (c)
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(June 2013,6M)(Jan 2015,6M)
8
...
The potential difference
across A is 0
...
3V
...
(Jan 2012,6M)(June 2014,6M)(Jan 2015,6M)
9
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If the current through 15Ω resistor is 3A find, (a)
the currents in 20Ω & 30Ω resistors, (b) the voltage across whole circuit, & (c) the total
power consumed in allresistor
...
Using Kirchhoff’s laws, determine R1, R2, I1,I2& I3 in the circuit shown in figure (d)
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For the network shown in figure (e), calculate the currents Ix&Iy
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Three 60W, 120V light bulbs are connected across a 120V power line as shown in the
figure (f)
...
(Jan 2011,6M)(June 2012,6M)(June 2013,6M)
13
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(Jan 2015,5M)

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

14
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5A
...


1(b) ELECTROMAGNETISM
1
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(Jan 2013,6M)(June 2014,5M)
2
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(Jan 2015,6M)
3
...
(Jan 2011,7M)(June 2014,8M)(June 2015,6M)

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

4
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(Jan 2015,5M)(June 2009,7M)
5
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(Jan 2010,5M)(June
2013,5M)(Jan 2015,5M)(June 2014,4M)(Jan 2014,5M)
6
...
(June 2014,6M)(June 2013,6M)
7
...
It is found that a current of 5A in coil A
produces flux of 0
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15mWb
...
(Jan
2013,8M)(June 2015,8M)(Jan 2012,8M)(June 2014,8M)
8
...
Calculate self-inductance, the emf induced & the energy stored when the current is
reversed in 0
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(Jan 2015,4M)(June 2014,4M)(Jan 2013,6M)
9
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1mWb
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The coil is moved in 0
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3mWb
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(Jan 2011,5M)(June 2012,5M)(Jan 2013,7M)
10
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Calculate the inductance &
energy stored in the magnetic field when a current of 2A flows in a solenoid
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A coil of 750 turns & a current of 10A gives rise to a magnetic flux of 1200µWb
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01 second
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Two identical coils of 1200 turns each, are placed side by side such that 60% of flux
produced by one coil links with the other
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12mWb
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(Jan 2015,8M)
13
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A current of 8A in coil A
produces a flux of 0
...
If the coefficient of coupling is 0
...
(b)flux linkage with coil B
...
02sec
...

14
...
If a current of 10A flowing in the first coil

Dept of EEE, SVIT

Basic Electrical Engineering

15ELE15/25

produces a flux of 0
...
Find the inductance of the second coil
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An air cored solenoid with length 30cm & internal diameter 1
...
Estimate its inductance & amount of energy stored in it when the current
through the coil rises from 0A to 5A

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