CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY
Question Bank
3 MARK --- QUESTION
4/5 MARK ----QUESTION
Course: DPMT
Semester: I Sem
Subject: Electrical & Electronics Engineering
2 Marks – Questions
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1. Define Voltage?
Ans: We define voltage as the amount of potential energy between two points
on a circuit. One point has more charge than another. This difference in charge
between the two points is called voltage. It is measured in Volts and denoted
with letter V
2. Define Current?
Ans: Current is the flow of charged particles through a conducting medium,
such as a wire.Its unit is Ampere and denoted with letter A
3. State ohm’s law
Ans: At constant temperature, the current through a conductor between two
points is directly proportional to the potential difference across the two
points and inversely proportional to the resistance,
The usual mathematical equation that describes this relationship:
4. Define Resistance?
Ans: Resistance: Resistance is the opposition that a substance offers to
the flow of electric current. It is represented by the uppercase letter R. The
unit of resistance is the ohm and denoted with the greek letter “Ω”
5. State Kirchhoff’s Current Law (KCL)
Ans: At any node (junction) in an electrical circuit, the sum of currents
flowing into that node is equal to the sum of currents
flowing out of that node or equivalently.
i2 + i3 = i1 + i4
6. Define Magnetic flux
Ans: The number of magnetic lines of forces set up in a magnetic circuit is
called Magnetic Flux.Magnetic flux is given the symbol Φ and is measured in
units called Weber (Wb).
7. Define MMF & Magnetic field intensity?
Ans: MMF: The force that produces magnetic flux is called Magneto Motive
Force(MMF)Magnetic field intensity: Force acting on a unit length of a
conductor carrying unit current placed perpendicularly inside the
magnetic field.
8. Define DC power?
Ans: The DC power is defined as the product of the voltage and current. It
is produced by the fuel cell, battery and generator.
It is measured in Watts.
P= V X I
9. Define Electromagnetism?
Ans: The phenomena associated with Electric and Magnetic fields and their
interactions with each other and with electric
charges and currents.
10. Define Time period & Power factor?
Ans: Time period: The time taken to complete one full cycle is called the
time period (T). A cycle consists of one complete
positive and one complete negative alternation.
Power factor: The power factor of an AC electrical power system is defined
as the ratio of the real power flowing to
the load, to the apparent power in the circuit
11. Explain the principle of DC generator?
Ans: It is based on Faraday's law of Electromagnetic Induction i.e whenever
a conductor cuts magnetic lines of force, an
emf is induced in the conductor.
12. What is back EMF in DC motor?
Ans: When the armature is rotated in a Magnetic field, then its conductors
cut the lines of force and an EMF is induced in them.
The induced EMF always opposes the applied EMF, hence it is called a back or counter EMF
13. Why starter is for DC motors?
Ans: Starters are used in DC motors to limit the high starting current
within about 2 to 3 times the rated current by adding
resistance in series with the armature circuit. Apart from starting resistances, starters are invariably fitted with protective devices such as
no voltage protection and over-load protection.
14. Give some applications of DC motors?
Ans: Shunt motors: Lathes, Centrifugal pumps, Blowers and Fans etc.
Series motors: Electric locomotives,
Trolley cars, Cranes and Hoists etc.
Compound motors: Elevators, Air
compressors, Rolling mills & Heavy planners etc.
15. Mention the two types of winding used in the DC machines?
Ans: Lap winding used for low voltage, high current machine Wave winding used for high voltage, low current machine
16. What do you mean by residual flux in DC generator?
Ans: The magnetic flux retained in the poles of the machine even without
field supplies called the residual flux.
17. What is the principle of operation of a DC Motor?
Ans: The operation of a D.C Motor based on the principle that when a
current carrying conductor is placed in a magnetic field,
the conductor experiences a mechanical force.
18. Define Torque?
Ans: Torque: The turning or twisting moment of a force about an axis is
called the torque, In the motor, it rotates the
armature abou the shaft.
19. Why starting current is high in a DC motor?
Ans: The absence of back emf at the time at starting causes the armature
current to shoot up to about 20 times the normal
current, if no limiting resistance is included.
20. What is the role of a Commutator?
Ans: The function of commutator is to facilitate the collection of current
from armature conductors. It converts the alternating
current induce in the armature conductors into unidirectional current in the external load circuit.
21. What is meant by a Transformer?
Ans: A transformer is a static device which transforms of electric power in
one circuit to another circuit without change in frequency.
22. What are the losses in Transformers, Explain?
Ans: Iron loss: Iron loss occurs in the transformers Iron core due to
hysteresis and eddy currents taking place. They are
almost fixed irrespective of loading of transformers.
Copper Losses: Copper losses are I2
R losses in the primary and the secondary windings of the transformer which
with the loading of transformer.
23. What is Auto-transformer?
Ans: In these transformer only one winding is used as primary and
secondary. Also, primary and secondary are conductively
coupled.
24. What is Current transformer?
Ans: They are protective devices used to measure very high value of current
in power system. The Current Transformer ( C.T.
), is a type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to
the current being measured in its primary
25. What is Buchholz relay?
Ans: It protects the transformer from their internal faults like earth
faults, winding short circuit, short circuit between phases,
Puncture of bushing etc..
26. What are the types of three phase induction motor?
Ans: 1. Squirrel cage induction motor
2. Slip ring induction motor
27. What is the SLIP?
Ans: This difference between the speed of the rotor and speed of the
rotating magnetic field in the stator is called slip. It is
the ratio between the relative speed of the magnetic field as seen by the rotor to the speed of the rotating field.
28. Describe the construction of a three phase motor?
Ans: A 3-phase induction motor has two main parts (i) stator and (ii)
rotor. The rotor is separated from the stator by a small
air-gap which ranges from 0.4 mm to 4 mm, depending on the power of the motor.
29. What is a Stator?
Ans: The stator consists of wound 'poles' that carry the supply current
that induces a magnetic field in the conductor. The number of
'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 6, etc.).
30. Why an Induction motor sometimes called Rotating Transformer?
Ans: An induction motor is sometimes called a rotating transformer because
the stator (stationary part) is essentially the
primary side of the transformer and the rotor (rotating part) is the secondary side.
31. Define Electrical Earthing?
Ans: The process of transferring the immediate discharge of the electrical
energy directly to the earth by the help of the low
resistance wire is known as the electrical earthing.
32. What is Fuse?
Ans: Fuse is used to protect an electric circuit when the rated current
exceeds in the circuit the fuse wire melts and opens the
circuit.
33. What is meant by Voltage Stabilization?
Ans: In order to obtain a stable voltage, the neutral point of a
transformer or an alternator is always earthed
34. What is meant by Earthed supply?
Ans: A neutral point is not a good earth point unless it is not connected
to earth. The conductor wire used for joining the neutral
point to the earth electrode is called the earthed supply.
35. What is Corona?
Ans: The phenomenon of violet glow, hissing noise and production of ozone
gas in an overhead transmission line is known
as Corona.
36. What is meant by Lightning arrestors?
Ans: A Lightning Arrestor is a device used in electrical power systems to
protect the insulation on the system from the damaging
effect of lightning
37. What is Skin effect?
Ans: The tendency of alternating current to concentrate near the surface of
a conductor is known as Skin Effect
38. Why do we require protection against lightning?
Ans: The lightning surges may cause serious damage to the expensive
equipments in the power system (e.g. generators,
transformers etc.) either by direct strokes on the equipment or by the strokes on the transmission lines that reach the equipment as travelling
waves.
39. What are advantages of leading power factor in distribution system?
Ans: 1. Losses in the form of heat is reduced
2. Cable becomes less bulky and easy
to carry, and very cheap to afford
3. It also reduces over heating of
transformers.
40. What are the common methods of Earthing?
Ans: 1. Plate Earthing
2. Pipe Earthing
3. Rod Earthing
4. Earthing through a water pipe
41. Define Semiconductor materials?
Ans: Materials having a conductivity of the order of somewhere between that
of conductors and insulators are called
semiconductors. Eg. Germanium and Silicon
42. What is an ideal diode?
Ans: An ideal diode is a two terminal polarity sensitive device that has
zero resistance when it is forward biased and infinite
resistance when reverse biased.
43. What are the types of Transistors?
Ans: Transistors are classified into three types:
1. Bipolar Junction Transistors
(BJTs)
2. Field Effect Transistors (FETs)
3. Insulated-Gate Bipolar
Transistors (IGBTs)
44. Explain about P-type and N-type semiconductors?
Ans: P-type: A P-type material is one in which holes are majority carriers
i.e. they are positively charged materials (++++)
N-type: A N-type material is one in
which electrons are majority charge carriers i.e. they are negatively charged
materials (-----)
45. What is meant by a Transistor?
Ans: Transistor is a semiconductor device capable of transferring the
signal from high resistance to
low resistance or vice versa.
Transistor has three terminals and is used in electronic circuits as
amplifiers and switches.
46. Write the truth table for AND gate
Ans:
47. Write the truth table for NOR gate
Ans:
48. Write the truth table for ENOR gate
Ans:
49. Write the truth table for NOT
gateAns:
50. Write the truth table for NAND gate
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