UPPCL JE Electrical question paper with Explanation Set-2 -2018

Ques.11. Which of the following falls under the category of the three-pin voltage regulator ICs?

  1. Both fixed voltage regulator and variable voltage regulator
  2. Adjustable AC voltage regulator
  3. Fixed voltage regulators
  4. Variable current regulators

A voltage regulator provides a constant dc output voltage that is essentially independent of the input voltage, output had current, and temperature. The voltage regulator is one part of a power supply. Regulator IC units contain the circuitry for reference source, comparator amplifier, control device, and overload protection all in a single IC. Although the internal construction of the IC is somewhat different from that described for discrete voltage regulator circuits, the external operation is much the same. IC units provide regulation of either a fixed positive voltage, a fixed negative voltage or an adjustable set voltage.

The IC voltage regulator is can be classified into three types

  1. Fixed voltage regulator
  2. Variable voltage regulator
  3. Switching regulator IC

Three Terminal Fixed Voltage Regulator

The fixed voltage regulator has an unregulated dc input voltage Vi applied to one input terminal, a regulated output dc voltage VO from a second terminal, and the third terminal connected to ground.

dixed voltage regulator

The capacitor Cin is required if the regulator is located at an appreciable distance, more than 5 cm from a power supply filter. The output capacitor CO may not be needed but if used it improves the transient response of the regulator i.e. regulator response to the transient changes in the load. This capacitor also reduces the noise present at the output. This IC provides a fixed regulated voltage of 5 to 24V.

Three Terminal Variable Voltage Regulator

Voltage regulators are also available in circuit configurations that allow to set the output voltage to a desired regulated value. The LM317 is an example of an adjustable voltage regulator, that can be operated over the range of voltage from 1.2 to 37V.

adjustable voltage regulato

Switching Regulator

The switching regulator is a type of regulator circuit whose efficient transfer of power to the load is greater than series and shunt regulators because the transistor is not always conducting.

  • The switching regulator passes voltage to the load in pulses, which are then filtered to provide a smooth dc voltage.
  • The switching regulator is more efficient than the linear series or shunt type.
  • This type of regulator is ideal for high current applications since less power is dissipated.
  • Voltage regulation in a switching regulator is achieved by the on and off action limiting the amount of current flow based on the varying line and load conditions.
  • With switching regulators 90°h efficiencies can be achieved.


Ques.12. Which of the following is a ferroelectric material?

  1. Barium titanate
  2. Potassium dihydrogen phosphate
  3. Rochelle salt
  4. All of these

Ferroelectricity, the property of certain nonconducting crystals, or dielectrics, that exhibit spontaneous electric polarization (separation of the center of positive and negative electric charge, making one side of the crystal positive and the opposite side negative) that can be reversed in direction by the application of an appropriate electric field.

In certain dielectric materials, polarization is not a linear function of the applied electric field. Such materials exhibit a hysteresis curves similar to that of ferromagnetic materials and are known as ferroelectric material The hysteresis curve exhibited by a ferroelectric material is shown in Fig.

ferroelectric material

Hysteresis Properties:-  When an increasing electric field is applied to a ferroelectric material, it results in an increase in polarisation and it reaches a maximum value for particular field strength. On the other hand, if we decrease the electric field, the polarisation decreases.

When the field strength is zero, i.e., E = 0, a small amount of polarisation exists in the material. This polarisation is known as remanent polarisation. Now the ferroelectric material is said to be spontaneously polarised. In order to reduce the value of polarization to zero, an electric field strength (-Ec) should be applied. This field is known as the coercive field.

Classification of Ferroelectric Crystals

Ferroelectric crystals are classified into three groups name

  1. Rochelle salt
  2. Potassium dihydrogen phosphate,
  3. Barium titanate

Rochelle Salt:- It behaves as a ferroelectric material in the temperature range from 255 to 296 i.e., it possesses two transition temperatures (Curie temperature). The crystal structure is orthorhombic above upper curie temperature. Below this transition temperature, the crystal structure is monoclinic in nature.

Potassium Dihydrogen Phosphate:- It has only one Curie temperature and its value is 123 K. It possesses ferroelectric property below this temperature. Above Curie temperature, its crystal structure is tetragonal. Below Curie temperature, the crystal structure is orthorhombic.

Barium Titanate:- This crystal exhibits three different ferroelectric phases. The transition temperatures of barium titanate are 278 K, 193 K and 393 K. The structure of barium titanate is cubic above 393 K. It has an orthorhombic structure when the temperature lies between 278 K and 193 K. Below 193 K, it has a rhombohedron structure.


Ques.13. Which of the following are cost-effective instruments?

  1. Active instrument
  2. Former is the passive instrument and later is active instrument
  3. Former is active instrument and later is passive instrument
  4. Passive instruments

There are many ways by which the instruments can be classified. Broadly the instruments are classified as,

  1. Active/passive instruments
  2. Null/deflection type instruments
  3. Monitoring/control instruments
  4. Analog/digital instruments
  5. Absolute/secondary instruments

Passive Instrument:- The instruments in which the output is produced entirely by the quantity being measured are called passive instruments.


A component whose output energy is supplied entirely or almost entirely by its input signal is commonly called a passive instrument. The output and input signals may involve energy of the same form (say, both mechanical), or there may be an energy conversion from one form to another (say, mechanical to electrical).

An example of such an instrument is a pressure gauge. As the liquid pressure changes, the piston moves to which pointer is connected. Thus the liquid pressure, due to which piston and hence pointer moves, is solely responsible for the measurement. No other input energy source other than liquid pressure is used in this instrument.

An active instrument, however, has an auxiliary source of power, which supplies a major part of the output power, while the input signal supplies only an insignificant portion. Again, there may or may not be a conversion of energy from one form to another.

An example of an active instrument is a float-type petrol tank level indicator. Here, the change in petrol level moves a potentiometer arm, and the output signal consists of a proportion of the external voltage source applied across the two ends of the potentiometer. The energy in the output signal comes from the external power source.

In the passive instrument, the resolution is less and cannot be increased very easily. In the active instrument, by adjusting the magnitude of the external energy input, control over resolution can be obtained. The passive instruments are simple to design and hence cheaper. The active instruments are complicated to design and hence costly. Depending on the required resolution, the passive or active instrument can be selected for measurement purpose.

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Ques.14. Which of the following is true for 3.9 k resistor using color-coding technique?

  1. Red, white, red, gold
  2. Red, green, orange, silver
  3. Orange, green, orange, silver
  4. Orange, white, red, gold

Resistor values can be known by the color band.

0 black

1 brown

2 red

3 orange

4 yellow

5 green

6 blue

7 violet

8 grey

9 white

First color = digit
Second color=digit
Third color= power of ten
Fourth color =tolerance

Now in the given question, the value of the resistor as 3.9 k i.e 3900 or 39 × 102ohm

3 = orange

9 = white

102 = Red

Hence color code of 3.9 K resistor is orange, white, and Red.


Ques.15. Which of the following generator is used in the thermal power plant?

  1. Turbo generator
  2. Synchronous motor
  3. Non-Salient pole synchronous generator
  4. Salient pole synchronous generator

The steam power plant is also called the thermal power plant. It is an important source to produce the electricity.

In thermal power plants, steam is generated by heating the water and is used to rotate the turbines which are coupled with the synchronous generators (also known as alternators) to produce electricity.

Steam can be generated from coal, gas, or nuclear as the main fuel. Coal, which is the main fuel used in thermal power plants, is fired in the boiler to generate heat for producing steam. The thermal efficiency of a steam power plant mainly depends on the choice of the steam cycle and varies from 28% to 35%.

The principal equipment of steam power plants is the boiler, super-heater, feed water pump, steam reheater, condenser, turbine, and generator. The major components of the steam-generating plants are shown in Figure. In a large thermal power plant unit, several stages of turbines such as high pressure, intermediate pressure and low pressure are used to extract more power from the steam and thus, increase the efficiency of the machine with minimum cost.

Thermal Power plant

For generating electricity using the steam turbine, high-speed synchronous generators are used because the efficiency of steam turbines is high at high speed. Since the speed of the turbo alternator is high, the diameters of the machine are kept minimum so that the centrifugal fort acting on the rotor is minimized. To keep the same electrical loading (which is proportional area x length), the length of the turbo-alternators is increased.


Ques.16. Which of the following is not a reason for undesirability of magnetic leakage in an electric machine?

  1. Produce fringing
  2. Lower the power efficiency
  3. Leads to their increased weight
  4. None of these

Magnetic leakage

ln a magnetic circuit, it is never possible to confine all the fluxes in the direction of the designated path, since a portion of the total flux will follow different paths from the intended path (generally through the air).

The shapes of these paths and the amount of flux in them depend on the geometry of the magnetic circuit and also in the value of the relative permeability, μr.

Therefore the part of the magnetic flux that has its path within the magnetic circuit is known as the useful flux or main flux and that taking other paths is called leakage flux. This phenomenon of wastage of some flux is called magnetic leakage. The sum of the two parts is called the total flux produced.

The ratio of the total flux produced by the magnet to the main flux is called leakage coeflicient or leakage factor.

Magnetic leakage in magnets is undesirable since it increases their weight as well as the cost of manufacturing.

Magnetic Fringing

When flux enters into the air gap, it passes through the air gap in terms of parallel flux lines. There exists a force of repulsion between the magnetic lines of force which are parallel and have the same direction. Due to this repulsive force, there is the tendency of the magnetic flux to  (spread out) at the edge of the air gap. This tendency of flux to spread out at the edges of the air gap is called magnetic fringing.

Magnetic Fringing

In electric machines like motors and generators, magnetic leakage is undesirable, because, although it does not lower their power efficiency, it leads to their increased weight and cost of manufacture. Magnetic leakage can be minimized by placing the exciting coils or windings as close as possible to the air gap or to the points in the magnetic circuit where the flux is to be utilized for useful purposes.


Ques.17. Which of the following is the correct definition of phasor?

  1. An instrument used for measuring phases of an unbalanced 3-phase load
  2. A line representing the magnitude and direction of an alternating quantity
  3. A line that represents the magnitude and phase of an alternating quantity
  4. A color tag or band for the distinction between different phases of a 3 phase system.

A quantity is called phasor if it satisfies the two criteria

it varies sinusoidally with time

It can be represented by the projection of a rotating vector

A phasor is a complex number representing a sinusoidal function whose amplitude (A), angular frequency (ω), and initial phase (θ) are time-invariant.



Ques.18. Which of the following is the correct formula of specific resistance?

  1. R/L
  2. RL/A
  3. RA/L
  4. A/RL

For any given material at a certain given temperature, the resistance is given as



Definition: The resistance of a material having unit length and the unit cross-sectional area is known as Specific Resistance or Resistivity.


where ρ is a constant and known as its specific resistance or resistivity.

l = Length in Meter

a = area of cross-section in m2

R = Resistance in Ohm

Specific Resistance depends only on the temperature and material of the conductor but not on its dimensions of the conductor, on which resistance depends, and mechanical deformation such as stretching etc. As ρ depends only on the material of a conductor at a given temperature, hence it is a characteristic constant.


Ques.19. Which of the following is the most common waveform of AC signals?

  1. Square
  2. Sinusoidal
  3. Saw Tooth
  4. Triangular

A waveform is a representation of how alternating current (AC) varies with time. The most familiar AC waveform is the sine wave or Sinusoidal Waveform, which derives its name from the fact that the current or voltage varies with the sine of the elapsed time. Other common AC waveforms are the square wave, the ramp, the sawtooth wave, and the triangular wave. 


Ques.20. Which of the following symbol represents the absolute permittivity of the dielectric medium correctly?

  1. εr
  2. εo
  3. εrεo
  4. εro

The permittivity of a medium is basically that property of the medium which permits electric flux to pass through it. If the permittivity is more it means that the medium allows more flux to pass through it and hence this medium is more susceptible to the electric field.

Absolute permittivity is the measure of the capacitance that is encountered when forming an electric field in a medium

The absolute permittivity of the material is given as

ε = εoεr

where ε = absolute permittivity of the dielectric material

εo =  permittivity of free space or vacuum

εr = relative permittivity of dielectric material in the capacitor


Absolute permittivity (ε) is the ratio of electric flux density in a dielectric medium to the corresponding electric field strength and is expressed as Farad/meter

ε = δ/E


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