BASIC ELECTRICAL ENGINEERING [BET-101]
MODULE-I
CH-1 [FUNDAMENTALS]
Q1.The unit of charge is__________
Ans. The unit of charge is “Coulomb”.
Q2.Define current and what is its unit?
Ans. The flow of free electrons in a definite direction in any
conductor or semiconductor
material is called electric current. Its unit is “Amper”(Amp. Or
A))
Q3.What is the unit of potential difference?
Ans. The unit of potential difference is “Volt”
Q4. What is resistance and what is its unit?
Ans. Resistance is the property of the material, by virtue of
which it opposes the flow of
electrons through it. Its unit is Ohm (Ω)
Q5. State Ohm’s law.
Ans. Ohm’s law states that at constant temperature the potential
difference between two ends of a conductor is directly proportional
to the current flowing between the two ends of that conductor.
Mathematically Vα I
V=RI (R is the constant of proportionality known as
resistance)
Q6. Define resistivity.
Ans. Resistivity is defined as the resistance offered by a
material of unit length and unit area
of cross section.
R=
==Ωm (Ohm-meter)
Unit is Ω-m or Ω-Cm
Q7. State conductivity.
Ans. Conductivity is the reciprocal of resistivity.
Mathematically conductivity σ = unit is Ω-1m-1
Q8. State Kirchhoff’s current law.
Ans. In any electrical network the algebraic sum of the currents
meeting at a point is zero.
∑ I =0
Q9. State Kirchhoff’s voltage law.
Ans. It states that the algebraic sum of all branch voltages
around any closed path of
a circuit is always zero.
∑IR + ∑e.m.f. = 0
Q10. State Superposition Theorem.
Ans. This theorem states that in any linear network containing
two or more sources, the resultant current in any element is equal
to the algebraic sum of the currents caused by individual sources
acting alone, while the other sources are non operative
That is while considering the effect of individual sources other
ideal voltage sources and ideal current sources in the network are
replaced by short circuit and open circuit across their
terminals.
Q11. State Thevenin’s theorem.
Ans. This theorem states that any two terminal linear network
having number of voltage, current sources and resistances can be
replaced by a simple equivalent circuit consisting of a single
voltage source in series with a resistance.
Where the value of voltage source is equal to the open circuit
voltage across the two terminals of the network and resistance is
equal to the equivalent resistance measured between the terminals
with all voltage sources are replaced by short circuit and current
sources by open circuit.
Q12. State maximum power transfer theorem.
Ans. A resistance load being connected to a DC network receives
maximum power when the load resistance is equal to the source
resistance (Thevenin’s equivalent resistance) of the source network
as seen from the load terminals.
Q13. State faraday’s laws of electromagnetic induction.
Ans. 1st Law: Whenever a conductor cuts the magnetic flux, an
e.m.f is induced in that
Conductor.
2nd Law: The magnitude of induced e.m.f is equal to the rate of
change of flux
Linkages.
Mathematically, e=-N volt.
Q14. State Fleming’s left hand rule.
Ans. According to Fleming’s left hand rule states that if the
thumb, the fore-finger & the middle finger of the left hand are
stretched to be perpendicular to each other. If the fore-finger
represents the direction of magnetic field, the middle finger
represents the direction of current, then the thumb represents the
direction motion of conductor. This rule is applicable for
motor.
CHAPTER-2
MAGNETIC CIRCUITS
Q1. What is absolute permeability and relative permeability?
Ans. Absolute permeability (µ) of a medium is given by the ratio
as follows
µ = =
Relative permeability (µr) of that medium is given by the ratio
as follows
µr = =
Q2. What is the value of µ0
Ans. The value of µ0 for free space is 4π X 10-7 H/m.
Q3. What is mmf?
Ans. It drives or tends to drive flux through a magnetic circuit
and corresponds to
electromotive force (e.m.f) in an electric circuit. It’s unit is
(AT)(Amper-Turn).
Q4. What is the relation between flux density (B), Magnetising
force(H) and absolute
permeability(µ)?
Ans. B=µH
Q5. Define Reluctance.
Ans. It is the property of the material which opposes the
creation of magnetic flux in it
Reluctance (S)= it’s unit is
Q6. What is permeance?
Ans. It is the reciprocal of reluctance.
Q7. What is the unit of ∅, B, H and S?
Ans. The unit of flux (∅) is weber(wb), Unit of flux density(B)
is wb/m2, Unit of Magnetising
force (H) is N/wb or AT/m and unit of Reluctance (S) is
Q8. Give two examples of ferromagnetic materials.
Ans. The examples of ferromagnetic materials are Iron, steel,
cobalt, Nickel
Q9.What is magnetic flux? What is it’s unit
Ans. A unit N-pole is supposed to radiate out flux of 1 weber.
It ‘symbol is ∅. It’s unit is weber.
CHAPTER-3
A.C THEORY
Q1.State two differences between AC &DC
Ans.
AC
DC
Alternating current is that current
in which magnitude as well as
the direction varies w.r.t time.
Direct current is that current in which the current flows at
constant magnitude either ‘+ve” (or) ‘-ve’ w.r.t time.
A.c. has certain frequency.
D.C has no frequency (or) Zero frequency.
Q2. Define Amplitude and frequency
Ans. Amplitude:- The maximum value (Positive or negative)
attained by an alternating quantity is called its amplitude or peak
value the amplitude of an alternating voltage or curve is denoted
by Vn (or Em) or Im.
Frequency:-The number of cycles that occur on one second is
called the frequency (f) of the alternating quantity. It is
measured in cycles/Sec. (c/sec) or Hertz(Hz) one Hertz is equal to
1c/sec.
Q3. Define Time period.
Ans. Time period:- The time taken in seconds to complete one
cycle of an alternating
quantity is called its time period. It is generally represented
by T.
Q4. What do you mean by phase angle and power factor?
Ans. Phase Angle:- Phase angle means the angle between the zero
position of reference and
the alternating quantity under consideration.
Power factor:- It is defined as the cosine of the angle of lead
& lag between the r.m.s
value of supply voltage and the r.m.s value of resultant
current.
It is also defined as the ratio of resistance &
impendance
Power factor= =
Q5. What is phase difference?
Ans. The difference in phase between two alternating quantities
is called phase difference.
Q6. State R.M.S Value.
Ans. The R.M.S value of an alternating current is defined as
that DC current which when flowing through a given circuit for a
given time produces the same heat as produced by the alternating
current when flowing through the same ckt for the same time. It is
also said to be the effective (or) virtual value of a.c.
Q7. What is form factor?
Ans. form factor is defined as the ratio
KF= = = 1.11
KF=1.11 (For sinusoidal only)
Q8.What is active Power?
Ans. Active power (P): It is the power which is actually
dissipated in the circuit resistance
i.e P=I2R = VI cos∅ Unit is in Watt or KWatt.
Q9. Explain Power Triangle
Ans. Suppose a series R-L circuit draws a current I when an
alternating voltage of r.m.s value V is applied to it. So the
current lags behind the applied by. Then three powers drawn by the
circuit is as follows:
(a)Apparent power(S) :
It is the product of r.m.s value of applied voltage and circuit
current
S=VI= (IZ)I=I2Z (Volt Amperes or Kilo Volt Amper)( VA or
KVA)
(b)Active power (P ) : It is the power which is actually
dissipated in the
circuit resistance i.e P=I2R = VI cos∅ (Watt or KWatt)
(c)Reactive power (Q) : It is the power developed in the
inductance
of the circuit Q = I2XL= VI sin∅ (Volt Ampere Reactive) (VAR or
KVAR)
10. Determine the impedance if resistance R=3Ω and inductive
reactance XL=4Ω
Ans. Impedance Z= = =5Ω
11. Determine the impedance if resistance R = 5Ω and capacitive
reactance
XC = 12Ω
Ans. Impedance Z= = =13Ω
Q12.. Form factor value in pure AC 50Hz sinusoidal
is__________
Ans. Form factor value in pure AC 50Hz sinusoidal is 1.11
Q13. Draw the waveform / phasor diagram of voltage & current
in the purely
resistive circuit.
Ans. Wave form Phasor Diagram
I
VR
Q14. Draw the phasor diagram of voltage & current for a.c
Through purely
inductive and capacitive ckt.
Ans. Phasor diagram of voltage & current for AC through
purely inductive ckt.
Phasor diagram of voltage & current for AC through purely
capacitive ckt.
Q15. Determine the impedance it resistance of 20Ω, an Inductance
of 0.2H and a
capacitance of 100µF are connected in series across 220 v, 50 Hz
mains ?
Ans. Inductive Reactance XL=2πfL=2xπx50x0.2=62.83Ω
Capacitive Reactance XC= = =31.83Ω
Impedance Z=
=
= 36.89Ω
Q16. Why power factor has no unit?
Ans. Power factor (Cos∅)= , The unit of resistance is Ω and also
impedance is Ω , So its ratio has no unit. Hence power factor has
no unit.
Q17. What is average value?
Ans. The average value of an alternating current is defined as
that steady current which transfers across any circuit the same
charge as is transferred by that alternating current during the
same time.
CHAPTER-4
GENERATION OF ELECTRIC POWER
Q1. Name one place where you will find a hydroelectric power
station in Orissa.
Ans:- Hirakud
Q2. Name any two radioactive elements.
Ans:- The radioactive elements are Uranium (U235), Thorium
(Th232) & Plutonium (Pu239) .
Q3. __________ is the main fuel used in Atomic Power plant.
Ans:- Uranium (U235)
Q4. What is the function of moderator in a nuclear plant?
Ans:- The function of moderator is to slow down the neutrons
before they bombard the fuel
rods. For moderator Carbon, Heavy water or Ordinary water are
used.
Q5. Reactor is used in which power station?
Ans:- Reactor is used in nuclear power station.
CHAPTER-5
CONVERSION OF ELECTRICAL ENERGY
Q1. Write main parts of DC machine.
Ans:- Main parts of DC machine are
i. Field magnets
ii. Armature
iii. Commutator
iv. Brush and Bearings
Q2. What are the functions of a commutator?
Ans:- The function of commutator in DC generator are
i. It facilitate the collection of current from armature
conductors
ii. It also converts AC current induced in the armature into
DC.
Q3. Sate back e.m.f.
Ans:- When the motor armature rotates an e.m.f is induced in
them by the law of electromagnetic induction whose direction is
found by Fleming’s right hand rule, is in opposite direction to the
applied voltage , because of its opposing direction it is referred
as back e.m.f (Eb )
Q4. Why starter is used to start DC motor?
Ans: In dc motors the armature is generally designed to have the
least resistance possible. So when starting a dc motor starter is
connected such that it limits the current value by being in series
with armature and later separates from the circuit. But by then
back emf develops in the armature.
Q5. Which motor is used for traction purpose and why?
Ans: DC series motor is used for traction purpose because it has
high starting torque which is important in traction system.
Q6. Write down the relationship between line current and phase
current in both star and delta connection.
Ans:- Star Connection: Iph=IL
Delta Connection: Iph=IL/√3
Q7. Explain the principle of operation of 3-phase induction
motor.
Ans:- It works on the principle that when a current carrying
conductor is placed within a magnetic field it experiences a
mechanical force.
Q8. Why capacitor is used in fan?
Ans:- Capacitor is used in fan to produce a phase shift . Which
enable it to produce a rotating magnetic field and make the motor
self starting.
Q9. Write down two uses of shaded pole induction motor.
Ans:- Shaded pole induction motors are used for hair dryers ,
Record players,
Tape recorders, projectors, photocopying machines
Q10. What is the function of brush in a DC generator?
Ans:- The function of brush is to collect the current from the
commutator and supply it to the
external load circuit.
Q11. Write down the principle of operation of a DC
generator.
Ans:- The principle of operation of DC generator based upon the
principle of dynamically induced e.m.f , according to Faraday’s
laws of electromagnetic induction whenever a conductor cuts
magnetic flux an e.m.f is induced in the conductor.
Q12. Write down the principle of operation of a dc motor.
Ans:- DC motor works on the principle that when a current
carrying conductor placed in a magnetic field it experiences a
force whose direction is given by Flemings left hand rule.
Q13. State the basic difference between a DC generator and a DC
motor.
Ans:- The basic difference between DC generator and DC motor is
that the DC generator converts mechanical energy to electrical
energy and DC motor converts electrical energy to mechanical
energy.
Q14. What a commutator does in a d.c. motor and in case of a d.c
generator?
Ans:- In DC motor commutator converts DC to AC and in DC
generator it converts AC to DC
Q15. Write down the different uses of a DC series motor.
Ans:-DC Series motors are used for i) Cranes ii) Trolley Cars
iii) Electric Locomotives
Q16. Line and phase relation of electrical quantities in star
connection.
Ans:- Vph=VL/√3
Iph=IL
Q17. Which type of motor is basically used for ceiling fan?
Ans:-Capacitor start and run single phase induction motor is
used for ceiling fan.
CHAPTER-6
WIRING AND POWER BILLING
Q1.Name types of wiring.
Ans. 1. Cleat wiring
2.Wooden casing and capping wiring
3.C.T.S. or batton wiring
4.Lead sheathed or metal sheathed wiring
5.Surface conduit wiring
6. Concealed conduit wiring
Q2. Which wiring is used for temporary purpose?
Ans:- Cleat wiring is used for temporary purpose
Q3. Use of fuse.
Ans:- A fuse is a short piece of metal, inserted in the circuit
, which melts when excessive current flows through it and thus
breaks the circuit.
Q4. List out the basic protective devices used in house hold
wiring.
Ans. The basic protective devices used in house hold wiring are
fuse and Miniature Circuit Breaker
Q5. Define power and its unit.
Ans. Power is the rate of doing work its unit is Watt or
Kwatt.
Q6. Define Energy.
Ans. Energy is the capacity of doing work. The amount of power
consumed for a certain period
of time
Q7. 1Kwhr is how much unit?
Ans. 1Kwhr is one unit.
Q8. Write down the advantages of conceal wiring.
Ans.1. There is no risk of mechanical injury
2. This wiring seems good and beautiful
3. There is no risk of electric shock
4. Durable and have a long life
5. The is no risk of fire
CHAPTER-7
MEASURING INSTRUMENT
GROUP-A
Q1. What is damping torque?
Ans:- The function of the damping device is to produce a damping
force while the moving system is in motion. The damping force
should be such that the pointer of the moving system comes to its
final steady state value quickly without any oscillation.
Q2. What is creeping?
Ans:- It is the phenomenon in which the energy meter still shows
some minimal energy consumption when there is no load attached to
the meter.
Q3. Draw the connection diagram of single phase wattmeter.
Ans.
Q4. Draw the connection diagram of energy meter.
Ans.
Q5. What is the function of controlling torque in indicating
instrument?
Ans. The function of controlling torque is to produces a force
equal and opposite to the deflecting force, so that pointer
deflects to a definite position of a particular magnitude of
current.
Q6. What are the methods of damping used in measuring
instrument?
Ans. The damping methods are Air friction damping, Eddy current
damping, Fluid friction damping.
CHAPTER-8
INTRODUCTION OF RENEWABLE POWER GENERATION
GROUP-A
Q1. What is renewable source of energy & what are they?
Ans. Renewable energy sources are those which are renewed at
least as quickly as they are consumed. They are solar energy, Wind
energy and Tidal energy etc.
Q2. What are the two methods of generation in solar power
plant?
Ans. 1. Conventional boiler method
2. Direct conversion method.
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