ARUNACHAL PRADESH PUBLIC SERVICE COMMISSION ITANAGAR
SUBJECT: ELECTRICAL ENCINEERINC PAPER
Time: 3 hours Full Marks: 200
Note: Answer Question No.1 and any four from the rest. All questions carry equal marks.
1. Answer any 10 10 x4 40

Define unit step and unit impulse forcing functions.


Current flowing in a series circuit having four equal resistances is I amperes. What is the magnitude ofthe current ifthe four resistances are connected in parallel?


Explain why moving iron instruments can be used to measure both A.C. and D.C.


Two resistors of 40 and 120 are connected in parallel and the combination is connected in series with a 20 resistor. If this circuit is connected across a 100 V supply, find the total current drawn.


Two capacitors of capacitance 32 IlF each are connected in parallel with a third capacitor of capacitance 64 IlF in series. Find the resultant capacitance.


Explain the diffusion and drift currents in a semiconductor.


What is the role of doping of impurities in pure silicon or germanium?


Establish the relation between Z and Y parameters of a two-port network.


What are active and passive transducers? Give examples of each type.


What VTVM stands for? What are the various types ofVTVM used in practice?


A capacitor of 40 IlF is charged to a potential difference of 500 V. Find the energy stored in the electric field between the plates of this capacitor.


Two sinusoidal currents are given by h 10 sin (wt and iz 15 sin What is the phase difference between them?


2. Attempt any 8 8x5=40

State Norton's theorem, and then write down the steps necessary to nortonize a given circuit.


State and prove maximum power transfer theorem.


What is s an lVDT? With the help of a neat sketch, explain its working principle.


What is Hall Effect? "Hall co-efficient of a p-type semiconductor is positive"-what is the significance of the statement?


What is meant by superconductivity? How is it affected by the application of a magnetic field?


What is a spectrum analyzer? Draw its simplified block diagram.


What do you understand by 'resonance in an A.C. circuit'? Distinguish between resonance in series circuit and resonance in parallel circuit.


What is a tQ-meter'? Explain its working principle.


Draw the block diagram of a general telemetering system, and state the function of each block.


Explain the 'Piezoelectric effect' observed in crystals, and state its applications.


1
A.E.(Elect)-2012/Electrical Engg. P-1
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3. Attempt any 5 5x8=40

A current of 120-j50 A flows through a circuit when the applied voltage is 8+j2 Determine


impedance, Power factor, power consumed, and reactive power.


A coil of power factor 0.6 is in series with a 100 capacitor. When connected to a 50 Hz supply, the p.d. across the coil is equal to the p.d. across the capacitor. Find the resistance and inductance ofthe coil.


Find the diffusion coefficients of electrons and holes of a single silicon crystal at 2rC, if the mobilities of the electrons and holes are 0.17 and 0.025 m2volrlsec-l respectively at 27°C.


What are the various ways of obtaining controlling torque in indicating instruments? Explain· each of them.


Draw the block diagram of a CRO, and state the function of each component.


Out of five batteries having internal resistance of 0.5 0 each, four are connected in parallel, and the remaining one is connected in series with them. Determine the resistance of a load that will draw maximum power from the source.


Write down the Maxwell's equations in differential and integral form for general case of time varying fields static fields


4. Answer any 4 4x 10 =40
In the circuit of the figure below, the switch s has been inthe position 1 fora long time. It is
thrown to position 2 at t find the current for t 0 and plot the variation of with t and
240
1

s
40
1
24V
....d 2HT 12V

I
A.E.(Elect)-2012JElectrical Engg. P·1
Use nodal analysis to find the voltage across and current through 4 0 resistor of the following network.
40


20
200

2A
2V

In a Wheatstone bridge three out of four resistors have a value of 1 KO each, and the fourth resistor equals 1010 O. If the battery voltage is 100 what is the approximate value of the open circuit voltage? If the output of the bridge is connected to a 4 KO resistor, how much current would flow through the resistor?


Derive the balance equations for an Anderson bridge.


What are n-type and p-type semiconductors? Explain with the help of energy diagram..


5. Answer any 2 2 x 20 =40
The 2-port network of the figure below is driven by a current source with Rs =2000 and is loaded with RL 20 O. The network parameters are: Yll 15X 10'3 mho, Y12 X10'3 mho, Y21 100 X 10'3 mho, and Yn 10 X 10'3 mho. Find the input resistance Vl/ll, the current gain 12/111 voltage gain V2/Vl/ the output resistance (Thevenin's resistance) presented to RL, and the power gain PG PJPs; where PL power loss in RL and Ps power supplied by the source.
11 12
2-port network

Rs



A uniform plane wave travelling in air is incident normally on an interface between air and dielectric. Dielectric has permeability of 110 and relative permittivity of €r =9. Calculate the reflection coefficient


the transmission coefficient


average incident power

average reflected power


average transmitted power


An inductance of 0.22 and 20 resistance is measured by comparison with a fixed standard inductance of 0.1 H and40 0 resistance. They are connected as shown in the figure below. A resistance of 750 0 is connected in arm CD and a resistance whose value is not known is in arm DA. Find the resistance of. arm DA, and show any necessary addition required to achieve both resistive and inductive balance.


B

o

6. Answer any 4 4xlO=40
Using Thevenin's theorem, find the current through the resistance R and the voltage across it, for the network shown in the following figure.
s!1 30


100 R=10Q
30V
•

A 50 Hz. Transmission line has a total series impedance of 40 +j125 n and a total capacitive shunt admittance of 10-3 U (mho). The receiving end load is 16.67 MW at 127 KV with 0.8

lagging power factor. Find the sending end voltage, current, power and power factor using nominal-n approximation.


Explain what is meant by network synthesis? Describe a method to achieve it.


Construct signal flow graph for the electrical network shown in the figure below:


R1L R2

i
Vi R3 C Vo
t0 t

A permanent magnet moving coil instrument gives full-scale reading of 25 mA when the p.d. across its terminals is 75 mV. Show how it can be used as an ammeter to for a range of 0-100 as a voltmeter for a range of 0-750 V.
7. Answer any 2 40

A coil of resistance 2 0 and an inductance 0.02 H is connected in series with a capacitor across 200 V mains. What capacitance must the capacitor have in order that the maximum current occurs at 25, 50, 100 Hz? Find also the current and the voltage across the capacitor in each case.


A voltage source delivers 4 A when the load resistance connected to it is 5 0 and 2 A when RL is 20 OJ calculate: the maximum power which the source can supply the power transfer efficiency of the source with RL 20 and the power transfer efficiency when the source delivers 60 W.


A 0.3 GHz plane wave is propagating in free space. The wave is incident normally on an infinite copper slab. For the transmitted wave in the copper slab, calculate the followings:


Attenuation constant


Phase constant




Skin depth

Phase velocity


Group velocity
Take cr 5.8 X 107 mho/m, Ilo and E Eo