Gujarat Technological University 2009 B.E Elements of electrical engineering, - Question Paper
GUJARAT TECHNOLOGICAL UNIVERSITY
B.E. Sem-II Remedial Examination September 2009
Seat No. Enrolment No.
Subject code: 110005 Subject Name: Elements of Electrical Engineering Date: 10/09/2009 Time: 03:00pm-5:30pm
Total Marks: 70
Instructions:
1. Write seat no. and enrolment no. at given location on question paper.
2. Attempt all questions.
3. Make suitable assumptions wherever necessary.
4. Figures to the right indicate full marks.
(a) State and explain Kirchhoffs laws.
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(b) Compare magnetic and electric circuits.
(c) Explain self induced e.m.f. and mutually induced e.m.f.
Q.2
(a) What is capacitor? Derive the expression for the equivalent capacitance of capacitors connected (i) in parallel (ii) in series.
(b) A 2 |iF capacitor is connected by closing a switch to a supply of 100 volts through 1 MQ series resistance. Calculate (i) time constant (ii) initial charging current (iii) the initial rate of rise of voltage across capacitor (iv) voltage across the capacitor 6 seconds after the switch has been closed.
(b) An iron ring of cross sectional area 6 cm2 is wound with a wire of 100 turns and has a saw cut of 2 mm. Calculate the magnetizing current required to produce a flux of 0.1 mWb if the mean length of magnetic path is 30 cm and relative permeability of iron is 470. Neglect leakage.
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Q.3
(a) What is coefficient of coupling? Derive expression for the same between two magnetically coupled coils.
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(b) The field winding of a generator has a resistance of 12.7 Q at 18oC and 14.3Q at 50oC. Find:
(i) temperature coefficient of resistance at 0oC
(ii) resistance at 0oC
(iii) temperature coefficient at 18oC
Q.3
(a) Prove that in a purely capacitive circuit power consumed is zero when a.c. voltage is applied. Draw relavent phasor diagram and waveforms.
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(b) An alternating current varying sinusoidally with a frequency of 50 Hz has r.m.s. value of 10A. Write down the equation for instantaneous value and find this value (i) 0.0025 second and (ii)
0.0125 second after passing through a positive maximum value.
(a) An inductive coil of resistance R and inductance L is connected in 08 parallel with a capacitor of C. Derive an expression for resonant
frequency and Q factor.
(b) A resistor of 40Q and an inductor of 0.2 H and capacitor of 120 |iF 06 are connected in parallel across 230V,50 Hz supply.
Find:
(i) the current of each branch (ii) the resultant current (iii) power factor of the circuit.
(a) Establish relationship between line and phase voltages and currents 08 in balanced delta connection. Draw complete phasor diagram of voltages and currents.
(b) Three identical coil each having resistance of 10 Q and reactance of 06 10 Q are connected in (i) star and (ii) delta across 400V, 3 phase supply. Find in each case line current and the reading of each of the two watt meters connected to measure the power.
(i) Cleat wiring (ii) conduit wring
(i) Ampere hour efficiency and (ii) Watt-hour efficiency of a battery
OR Q.5
(b) Explain construction and working of high pressure mercury vapor 04 lamp.
(c) Explain the working of a miniature circuit breaker. 04
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| Earning: Approval pending. |
