VTU First Year Engineering (P Cycle) (Semester 2)
Basic Electrical Engg.
June 2014
Total marks: --
Total time: --
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Choose the correct answer for the following :-
1 (a) (i) The resistance of a conductor is directly proportional to its ______ and inversly proportional to its _____
(A) Length & Area
(B) Area & Length
(C) Length & Current
(D) Length & Voltage
1 M
1 (a) (ii) When the conductor moves perpendicular to the lines of flux, the emf induced is _____
(A) Minimum
(B) Maximum
(C) Zero
(D) None of these
1 M
1 (a) (iii) The mutual inductance between two coils of self inductance 0.8 H and 0.2 H, have a co-efficient of coupling 0.9 is _____
(A) 0.36 H
(B) 0.4 H
(C) 0.16 H
(D) 0.144 H
1 M
1 (a) (iv) An electric heater is rated to 2 kW, 200 V. the resistance of the heater coil is _____
(A) 10 ?
(B) 0.1 ?
(C) 20 ?
(D) 200 ?
1 M
1 (b) Show that the equivalent resistance of two resistors connected in parallel in the ratio of the product of these two resistances divided by the sum of those two resistance values.
4 M
1 (c) Derive an expression for dynamically induced emf.
6 M
1 (d) Two coils having 1000 turns and 1600 turns respectively are placed close to each other such that 60% of the flux produced by one coil. If a current of 10 A, flowing in the first coil, produces a flux of 0.5 mwb. Find the inductances of the second coil.
6 M

Choose the correct answer for the following :-
2 (a) (i) An alternating current is given by \[ i=14.14 \sin \left ( \omega t+ \dfrac {\pi}{6} \right) \] has an rms values of _____ amperes.
(A) 10 A
(B) 14.14
(C) 20 A
(D) 0.707
1 M
2 (a) (ii) In an a.c. circuit, the ratio of kW.KVA represents _____
(A) Power factor
(B) Load factor
(C) Form factor
(D) Peak factor
1 M
2 (a) (iii) A current drawn by a capacitor of 20 ?F is 1.382 A from a 220 V A.C. supply. The supply frequency is ______
(A) 25 Hz
(B) 60 Hz
(C) 50 Hz
40 Hz
1 M
2 (a) (iv) The unit of apparent power is _____
(A) kW
(D) Joules
1 M
2 (b) Define :-
(i) Instantaneous value
(ii) Amplitude
(iii) Cycle
(iv) Period with
4 M
2 (c) Two impedances (150-j157) ? and (100 + j110) ? are connected in parallel across 200 V, 50 Hz supply. Find branch currents, total current and total power consumed in the circuit. Draw the phasor diagram.
6 M
2 (d) Show that the power consumed in an R-C series circuit is VIcos?. Draw the waveform for voltage, current and power.
6 M

Choose the correct answer for the following :-
3 (a) (i) The phase sequence of a three phase system is RYB. The other possible phase sequence is _____
(D) None of these
1 M
3 (a) (ii) When the two wattmeters used to measure three phase power gives equal readings, then the p.f. of the circuit is given by _____
(A) 0
(B) 0.5
(C) 1
(D) 0.866
1 M
3 (a) (iii) The power consumed by a 3-? load is given by the expression _____
\[ (A)\ 3V_LI_L\cos \phi \\(B)\ V_LI_L\cos \phi \\(C)\ \sqrt{3}V_LI_L\cos \phi \\(D)\ \sqrt{3}V_L\cos \phi \]
1 M
3 (a) (iv) A 3-? apparatus is _____ efficeint than a 1-? apparatus,
(A) More
(B) Less
(C) Both A and B
None of these
1 M
3 (b) What are the advantages of 3-? system over a single phase system?
6 M
3 (c) A 3-?, 400 V, motor takes an input of 40 kW at 0.45 p.f. lag. Find the reading of each of the two single phase wattmeters connected to measure the input.
5 M
3 (d) Obtain the relationship between line current and phase current in a balanced 3-? delta connected system.
5 M

Choose the correct answer for the following :-
4 (a) (i) The totating disc of the energy meter is made of _____
(A) Copper
(B) Silver
(C) Aluminium
(D) Platinum
1 M
4 (a) (ii) One unit of electrical energy is equivalent to _____
(A) 3.6 kWs
(B) 3600 W.S
(C) 1 kWH
(D) 10 WH
1 M
4 (a) (iii) An intermediate switch is used in _____ of lamps.
(A) Three way control
(B) Two way control
(C) One way control
(D) Four way control
1 M
4 (a) (iv) The value of Fusing Factor is always _____
(A) Less than 1
(B) Equal to 1
(C) Zero
(D) More than 1
1 M
4 (b) With the help of neat diagram, explain the construction and principle of operation of a single phase induction type energy meter.
8 M
4 (c) Write the circuit diagram and switching table for two-way and three-way control of lamp. Where is it used?
8 M

Choose the correct answer for the following :-
5 (a) (i) The purpose of commutator in a d.c. genrator is to _____
(A) Increases output voltage
(B) Convert emf from AC to DC
(C) Reduce sparking at brushes
(D) Increases the speed
1 M
5 (a) (ii) In a lap winding, the number of parallel paths is equal to _____
(A) P/2
(B) 2P
(C) P
(D) 4P
1 M
5 (a) (iii) The speed of a d.c. _____ motor is almost constant.
(A) Shunt
(B) Series
(C) Compound
(D) None of these
1 M
5 (a) (iv) The torque produced by DC motor is directly proportional to _____
(A) VIa
(B) IaRa
(C) ?Ia
(D) EbIa
1 M
5 (b) Derive the expression for the e.m.f. of a DC generator.
4 M
5 (c) Sketch the various characteristics of DC shunt motor and mention its applications.
6 M
5 (d) A DC shunt motor takes an armature current of 110 A at 480 V. The armature resistance is 0.2 ?. The machine has 6 poles and armature is lap connected with 864 conductors. The flux per pole is 0.05 Wb. Calculate :-
(i) speed
(ii) the torque developed by the armature.
6 M

Choose the correct answer for the following :-
6 (a) (i) The transformation ratio in a transformer is equal to _____
\[ (A)\ \dfrac {E_1}{E_2}\\(B)\ \dfrac {N_1}{N_2}\\(C)\ \dfrac {N_2}{N_1}\\(D)\ \dfrac {I_2}{I_1}\]
1 M
6 (a) (ii) The effficiency of a transformer is maximum when _____
(A) Iron loss is more than copper loss
(B) Iron loss is equal to copper loss
(C) Iron loss is less than copper loss
(D) None of these
1 M
6 (a) (iii) Core type of transformers are used to handle ______ and _____ voltages.
(A) Low and High
(B) Low and Medium
(C) High and Medium
(D) None of these
1 M
6 (a) (iv) Copper loss in a transformer is a ______ loss.
(A) Constant loss
(B) Variable loss
(C) Friction loss
(D) None of these
1 M
6 (b) Explain the construction and working of a transformer.
6 M
6 (c) Find the number of turns on the primary and secondary side of a 440/230 V, 50 Hz single phase transformer, if the net area of cross section of the core is 30 cm2 and the maximum flux density is 1Wb/m2.
4 M
6 (d) A single phase transformer working at 0.8 pf has an efficiency 94% at both three fourth full load and full load of 600 kW. Determine the efficiency at half full-load unity power factor.
6 M

Choose the correct answer for the following :-
7 (a) (i) A non salient pole rotor is used in ______ alternator.
(A) Low speed
(B) High speed
(C) Medium speed
(D) A and B
1 M
7 (a) (ii) The speed at which a 4-pole alternator has to be derive to generate a voltage at 50 Hz is ______
(A) 1000 rpm
(B) 1500 rpm
(C) 2000 rpm
(D) 1440 rpm
1 M
7 (a) (iii) The E.M.F. induced in an alternator is given by the equation ______
(A) 4.44 f ? z kp kd
(B) 2.22 kp f ? z
(C) 2.22 f ? z kp kd
(D) 4.44 f ? z
1 M
7 (a) (iv) The field winding of an alternator is ______ excited.
(A) DC
(B) AC
(C) Both DC and AC
(D) None of these
1 M
7 (b) How are alternators classified? With a neat diagram, show the difference between them.
8 M
7 (c) A 2-pole, 3-phase alternator running at 3000 rpm has armature slots with 2 conductors in each slot. Calculate the flux per pole required to generate a line voltage of 2300 V. Distribution factor is 0.952 and pitch factor is 0.956.
6 M
7 (d) Define regulation of an alternator.
2 M

Choose the correct answer for the following :-
8 (a) (i) The frequency of the rotor current is _____
(A) s/f
(B) sf
(C) sf2
(D) None of these
1 M
8 (a) (ii) In a 3-phase induction motor, the slip speed is given by _____
(A) Ns
(B) N
(C) Ns-N
(D) N-Ns
1 M
8 (a) (iii) The synchronous speed of three phase induction motor is given by _____
\[ (A)\ N_S=\dfrac {120 \ f}{P}\\(B)\ N_S=120 \ fP\\(C)\ \dfrac {120P}{f}=N_S\\(D)\ N_S=\dfrac {Pf}{120}\]
1 M
8 (a) (iv) A 3-? induction motor having 4-poles, 50 Hz runs at 1440 rpm, the slip is _____
(A) 3%
(B) 5%
(C) 4%
(D) 1%
1 M
8 (b) With a neat diagram, explain the working principle of 3-? induction motor.
6 M
8 (c) A 10 pole induction motor is supplied by a 6-pole alternator which is driven at 1200 rpm. If the motor runs with a slip of 3% what is its speed?
6 M
8 (d) Why does an induction motor need a starter?
4 M

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