Lingaya's University Previous Year Papers

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Q-1. Part – A
Select the correct answer of the following multiple choice questions. [10x1=10]
(i) To determine the polarity of voltage drop across a resistor, it is necessary to know the
(a) Value of resistance
(b) Direction of current in the resistance
(c) Value of current in the resistance
(d) Value of resistance & direction of current
(ii) The peak value of sine wave is 100. The rms value is
(a) 70.7 (b) 50 (c) 35.35 (d) 100
(iii) The internal resistance of a circuit is 16 ohm. For maximum power transfer, the load resistance should be
(a) 4 ohm (b) 6 ohm (c) 16 ohm (d) 20 ohm
(iv) Open circuit test of a transformer provides
(a) Copper loss (b) Core loss
(c) Copper & core loss (d) None of these
(v) Value of slip in an induction motor is
(a) N-Ns (b) Ns-N (c) Ns (d) N
(vi) Reluctance in a magnetic circuit is analogous to
(a) Conductance (b) Inductance
(c) Capacitance (d) Resistance
(vii) A moving coil ammeter is used to measure
(a) A.C. & D.C. current (b) Only A.C. current
(c) Only D.C. current (d) None of these
(viii) The maximum value of power factor in A.C. circuit is
(a) 0 (b) 1 (c) Between 0 & 1 (d) -1
(ix) A material for permanent magnet should have
(a) High retentivity (b) High permeability
(c) Low hysteresis loss (d) High hysteresis loss
(x) Core of a transformer is laminated to reduce
(a) Hysteresis loss (b) Eddy current loss
(c) Hysteresis & eddy current loss (d) Copper loss

Part – B

(a) State & explain Norton’s theorem. [5]
(b) Derive emf equation of a transformer. [5]

Section – B

Q-2. (a) Draw and explain equivalent circuit of a transformer. [6]
(b) Explain principle, construction & working of a transformer. [7]
(c) Explain efficiency of a transformer. Derive the condition for maximum efficiency. [7]

Q-3. (a) Explain the principle of operation of three phase induction motor.
(b) Explain various methods of speed control of D.C. motor. [2x10=20]

Q-4. (a) Explain principle, construction & working of energy meter.
(b) Explain principle, construction & working of moving coil ammeter. [2x10=20
Q-5. (a) A 4700  resistor and 2 micro-farad capacitor are connected in parallel across a 240V, 60 Hertz source. Determine circuit impedance and line current. [10]
(b) Determine Thevenin’s equivalent circuit which may be used to represent the given network at the terminal AB (figure – 1) and find the current in branch AB. [10]

Q-6. (a) Define following:-
(i) Permeance (ii) Reluctance (iii) Permeability
(iii) Reluctivity (v) Magnetic field intensity [5]
(b) Explain hysteresis phenomenon. [6]
(c) An iron ring is composed of three sections. The cross-sectional area is 0.001 sq. m. for each section. The mean arc length are La = 0.3 m, Lb = 0.2, Lc = 0.1 m. An air gap of 0.1 mm is cut in the ring. Relative permeability for section a, b and c are 5000, 1000 and 10000 respectively. Given 0 = 4 x 10-7. Find reluctances of sections including air-gap. [9]