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Elements of Electrical Engineering : Question Paper May 2016 - First Year Engineering (Semester 1) | Gujarat Technological University (GTU)

## Elements of Electrical Engineering - May 2016

### First Year Engineering (Semester 1)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
1(a)(i) The unit of current is _______
(a) Volt/sec   (b) coulomb/sec   (c) amp/sec   (d) none of these
(1 marks)
1(a)(ii) Coulomb's second law is called as _______ law
(a) Inverse square   (b) charge   (c) induction
(1 marks)
1(a)(iii) If the length of conductor is doubled and its cross sectional area is reduced to 50% then its resistance will be _______
(a) Same   (b) doubled   (c) increased by 4 times   (d) reduced to a magnetic
(1 marks)
1(a)(iv) A conductor carries 10A in a direction perpendicular to a magnetic field of density 0.3T. If the length of conductor is 10 cm the force on the conductor F= _______
(a) 3N   (b) 0.3N   (c) 30N
(1 marks)
1(a)(v) Amount of light produced by a lamp or the amount of heat produced by an iron is proportional to the
(a) Square of RMS value   (b) RMS value   (c) square of average value   (d) average value
(1 marks)
1(a)(vi) The three phase voltages are displaced by _______ radians from each other.
(a) π/2   (b) π/3   (c) 2π/3   (d) π
(1 marks)
1(a)(vii) Define Lumens.(1 marks) 1(b)(i) The resistance of a thin conductor is _______ as compared to that of a thick conductor.
(a) Same   (b) lower   (c) higher
(1 marks)
1(b)(ii) The value of relative permittivity for Air is _______ .(1 marks) 1(b)(iii) A magnetic circuit has mean length of 20 cm and cross sectional area of 1 cm2 if the flux density is 2T then ϕ = _______ .
(a) 210-4 mWb   (b) 210-4 Wb   (c) 2*10-2 Wb   (d) none of these
(1 marks)
1(b)(iv) Define RMS value.(1 marks) 1(b)(v) Draw the phasor diagram of R-C series circuit.(1 marks) 1(b)(vi) For a balanced delta load the _______ of all their line currents is zero.
(a) Product   (b) difference   (c) sum   (d) division
(1 marks)
1(b)(vii) Define A-H efficiency.(1 marks) 2(a) Explain the effect of temperature on different metals.(3 marks) 2(b) Explain Current and Voltage divider rule.(4 marks) 2(c) Derive expression for delta to star conversion of resistive network.(7 marks) 3(a) Derive the expression for the equivalent capacitance of capacitors connected in parallel.(3 marks) 3(b) The equivalent capacitance of two capacitors when connected in series is 0.03 μF & when connected in parallel is 0.16 μF. Find the capacitance of both the capacitors.(4 marks) 3(c) Three capacitors having capacitances of 10 μF, 20 μF and 40 μF are connected in series to a 400 V d.c. source. Find (i) Total capacitance (ii) Total charge in circuit (iii) Total energy stored.(7 marks) 4(a) Explain Magnetic Hysteresis phenomena using hysteresis loop.(3 marks) 4(b) State similarities between magnetic circuit and electrical circuit.(4 marks) 4(c) Define co-efficient of coupling. Derive the relation between self and mutual inductance.(7 marks) 5(a) Three currents are represented by i1 = 10sinwt, i2 = 20sin(wt-π/6) ,i3 = 30sin(wt+π/4) . Find magnitude and phase angle of resultant current of their addition.(3 marks) 5(b) An inductive coil draws 10 A current and consume 1 KW power from a 200V, 50Hz, Ac supply determine (1) the impedance in Cartesian and polar form (2) power factor (3) reactive and apparent power.(4 marks) 5(c) Prove the condition of resonance for series R-L-C AC circuit. Also analyze the phenomena with the help of graph.(7 marks) 6(a) Give advantages of Two Wattmeter Method.(3 marks) 6(b) For a balanced delta connected load supplied at 3-phase, 400 V ac supply, the two wattmeter readings are: 7.8kW and ??? 2.55kW. Find out load power factor & line current.(4 marks) 6(c) Establish relation between line voltage & phase voltage and current relation in 3-phase star connection. Draw phasor diagram.(7 marks) 7(a) Classify various types of Lighting scheme and explain any two.(3 marks) 7(b) State types of Fuse and explain any one.(4 marks) 7(c) Explain construction of cable in detail.(7 marks)