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BASIC ELECTRICAL ENGINEERING, exam papers, Exams of Network Theory

Jamia Millia IslamiaNetwork Theory

B.Tech Semester Regular Examinations, June 2009 BASIC ELECTRICAL ENGINEERING Exams on network theory, Kirchoffs laws, mutual induction, series circuit,parallel circuit, Root Mean Square, RMS i. Slip speed ii. Slip iii. Synchronous Speed iv. Torque.

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Code No: R07A1EC07 Set No. 1
I B.Tech Semester Regular Examinations, June 2009
BASIC ELECTRICAL ENGINEERING
( Common to Computer Science & Engineering, Information Technology
and Computer Science & Systems Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
⋆⋆⋆⋆⋆
1. Use Kirchoffs laws to determine the magnitude and polarity of the source S if the
current through the branch BD is 0.2A from D to B in the circuit as shown in figure
1. [16]
Figure 1
2. (a) Give a detailed comparison of series and parallel circuit.
(b) What are the applications, merits and demerits of a series circuit?
(c) What are the applications and advantages of a parallel circuit? [6+5+5]
3. (a) Explain self induction and mutual induction in detail. Also derive the expres-
sion for dynamically induced emf.
(b) Two identical 2000 turns coil X and Y lie in parallel planes, such that 60% of
the magnetic flux produced by one coil links the other. A current of 5A in the
coil X produces a magnetic flux of 0.07mwb in it. If the current in X changes
from 7A to -7A in 0.03 sec, what will be the magnitude of the emf induced in
X? Also calculate the self inductance of each coil and mutual inductance.
[6+10]
4. (a) Why are the Root Mean square values of alternating quantities more important
than their average values?
(b) Find the Root Mean Square of the resultant current in a conductor which
carries simultaneously sinusoidal alternating current with a maximum value
of 10A and direct current of 10A.
(c) A current wave is represented by the equation i = 20 Sin251t. Calculate the
maximum and RMS value of current and its frequency. [4+6+6]
5. (a) Explain the construction of a single phase transformer.
1 of 2
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I B.Tech Semester Regular Examinations, June 2009 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆ ⋆ ⋆ ⋆ ⋆

  1. Use Kirchoffs laws to determine the magnitude and polarity of the source S if the current through the branch BD is 0.2A from D to B in the circuit as shown in figure
    1. [16]

Figure 1

  1. (a) Give a detailed comparison of series and parallel circuit. (b) What are the applications, merits and demerits of a series circuit? (c) What are the applications and advantages of a parallel circuit? [6+5+5]
  2. (a) Explain self induction and mutual induction in detail. Also derive the expres- sion for dynamically induced emf. (b) Two identical 2000 turns coil X and Y lie in parallel planes, such that 60% of the magnetic flux produced by one coil links the other. A current of 5A in the coil X produces a magnetic flux of 0.07mwb in it. If the current in X changes from 7A to -7A in 0.03 sec, what will be the magnitude of the emf induced in X? Also calculate the self inductance of each coil and mutual inductance. [6+10]
  3. (a) Why are the Root Mean square values of alternating quantities more important than their average values? (b) Find the Root Mean Square of the resultant current in a conductor which carries simultaneously sinusoidal alternating current with a maximum value of 10A and direct current of 10A. (c) A current wave is represented by the equation i = 20 Sin251t. Calculate the maximum and RMS value of current and its frequency. [4+6+6]
  4. (a) Explain the construction of a single phase transformer.

(b) Discuss in detail the difference between a core type and a shell type trans- former. [10+6]

  1. (a) Give the reasons for the following

i. A series motor should not be connected to a load through a belt ii. A series motor develops a high starting torque iii. A differential compound motor is very rarely used iv. A shunt motor runs at almost constant speed irrespective of load current. (b) How may the direction of rotation of dc shunt motor be reversed? What is the effect of reversing the line terminals? [12+4]

  1. (a) Define:

i. Slip speed ii. Slip iii. Synchronous Speed iv. Torque. (b) Why is an induction motor called a rotating transformer? Justify. (c) A three phase induction motor is wound for 4 poles and is supplied from 50 Hz system. Calculate synchronous speed , rotor sped when slip is 4% and rotor frequency when rotor runs at 600 rpm. [8+2+6]

  1. Explain with neat sketch the construction and working of a MI ammeter and MC ammeter. [8+8]
  1. Three impedances Z1=10+j31.4 Ω, Z2 = 6+j8 Ω, and Z3 = 3-j4 Ω are connected in parallel across a 200V AC supply. Calculate

(a) Total admittance, conductance and susceptance of the whole circuit. (b) Total current, power factor and power. [8+8]

  1. (a) Explain the principle of working of a single phase transformer.

(b) Derive from the first principles, the emf equation of a single phase transformer. [8+8]

  1. (a) How is the efficiency of the dc motor determined by the direct loading method? Derive the equation for efficiency. (b) In a brake test on a dc shunt motor full load readings are as follows. Tension on tight side is 9.1 Kg, tension on slack side is 0.8 Kg. Total current is 10 A, supply voltage is 110V, speed is 132 rpm, effective radius of the pulley is 7. cm. Calculate its full load efficiency. [8+8]
  2. Explain in detail the construction of a three phase induction motor specifying in detail the squirrel cage and slip ring rotor construction. [8+8]
  3. (a) Bring out the advantages and disadvantages of MI and MC instrument.

(b) Bring out the differences between various methods of producing controlling torque. [8+8]

I B.Tech Semester Regular Examinations, June 2009 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆ ⋆ ⋆ ⋆ ⋆

  1. (a) Six resistors are connected as shown in figure 1a. If a battery having an emf of 30V and an internal resistance of 2Ω is connected to terminals A and B. Find i. current from battery ii. potential difference across 10Ω and 12Ω.

Figure 1a (b) Find the effective resistance of the following combination of resistances and the voltage drop across each resistance when the applied voltage is 70V across P and Q as shown in figure 1b. [8+8]

Figure 1b

  1. Determine the power loss in the 10Ω resistor by using thevenins theorem as shown in figure 2. [16]

(c) A 3 phase star connected 8 pole, 750 rpm alternator has 3 slots per pole per phase. The conductors per slot are 8, while flux per pole is 0.62 Wb. Calculate the induced emf per phase. [6+5+5]

  1. (a) Give a comparison of spring control and gravity control.

(b) Explain the errors occurring in a moving iron instrument. [8+8]

I B.Tech Semester Regular Examinations, June 2009 BASIC ELECTRICAL ENGINEERING ( Common to Computer Science & Engineering, Information Technology and Computer Science & Systems Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆ ⋆ ⋆ ⋆ ⋆

  1. (a) State i. Flemings right hand rule ii. Flemings left hand rule iii. Kirchoff’s laws iv. Lenz’s law. (b) A cable has a resistance of 12Ω. What will be the resistance of another cable of the same material twice as long as and half the cross sectional area? (c) If the piece of certain wire of 40m length and 0.07cm in radius has a resistance of 15Ω, find the specific resistance of the material. [8+4+4]
  2. (a) Give a detailed comparison of series and parallel circuit. (b) What are the applications, merits and demerits of a series circuit? (c) What are the applications and advantages of a parallel circuit? [6+5+5]
  3. (a) Write short notes on : i. Magnetic leakage ii. Retentivity (b) A conductor 12cm in length with a uniform velocity of 2m/s at right angles to itself and to a uniform magnetic field having a flux density of 1wb/sq.m. Calculate the induced emf between the ends of the conductor. (c) Find the reluctance of path given relative permeability = 800, length = 75cm and diameter = 2.5cm. [4+6+6]
  4. (a) Explain the terms i. In-phase vectors ii. Lead-Lag vectors. (b) Calculate the current, power, power factor and voltage across the resistor of 8 Ω in series with a inductor of 20H and a capacitor of 14 μF excited by an AC supply of 110 V. [6+10]
  5. (a) What is the difference between an ideal transformer and a practical trans- former? (b) Derive the approximate equivalent circuit of a 1 phase transformer. [4+12]