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Elements of Electrical Engineering : Dec 2013 - First Year Engineering (Semester 1) | Gujarat Technological University (GTU)

## Elements of Electrical Engineering - Dec 2013

### 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.

### Objective question

1 (a) (i) Define : rms value for alternating circuit.(1 marks) 1 (a) (ii) Three equal resistance of magnitude 5 Ohm each are connected in delta. The resistance between any two pair of terminals of thedelta will be _________ ohms.(1 marks) 1 (a) (iii) Write Lenz law.(1 marks) 1 (a) (iv) Define power factor. (1 marks) 1 (a) (v) The Q factor of coil is given by _________(1 marks) 1 (a) (vi) A 12µ resistor, a 40 µF capacitor, and an 8mH coil are in series across an ac source. The resonant frequency is _______(1 marks) 1 (a) (vii) To tune a parallel resonant circuit to a higher frequency, the capacitance should be(1 marks) 1 (b) (i) Write any one similarity between electric and magnetic circuit(1 marks) 1 (b) (ii) The R.M.S. value of a half wave rectified sinusoidal alternating current with peak value Im is ____________.(1 marks) 1 (b) (iii) Write function of 'fuse' in electrical circuit.(1 marks) 1 (b) (iv) The 'gauss' is unit of __________ .(1 marks) 1 (b) (v) Write ohm's law.(1 marks) 1 (b) (vi) The five 0.050uF capacitors are connected in parallel. The equivalent capacitance is _____________(1 marks) 1 (b) (vii) Define luminance (1 marks) 2 (a) Establish relationship between line and phase voltages and currents in balanced delta connection. Draw complete phasor diagram of voltages and currents.(7 marks) 2 (b) Explain series resonance circuit. Draw resonance curve.(7 marks) 3 (a) An inductive coil of resistance R and inductance L is connected in parallel with capacitor of C. Derive an expression for the resonant frequency and Q factor.(7 marks) 3 (b) An iron ring has mean diameter of 57.3 cm. It carries a coil having 450 turns and the current flowing through coil is 2 A. The relative permeability of the iron is 1200. Calculate the flux density produced.(7 marks) 4 (a) Define temperature co-efficient of resistance. How does the resistance of different materials vary with temperature? Prove that αt=?0/(1+ α0t) and α2=1/[(1/α1)+(t2-t1)](7 marks) 4 (b) Three capacitors having capacitances of 10μF, 20μF and 40μF 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) 5 (a) Derive the expression for the decay of current in an inductive circuit. Define time constant.(7 marks) 5 (b) A coil resistance 15Ω and inductance 0.05 H is connected in parallel with a noninductive resistance of 20 Ω. The circuit is connected across 200 V, 50 Hz supply. Determine (i) current in each branch (ii) total current supplied (ii) power factor of the combination.(7 marks) 6 (a) Prove that current in purely capacitive circuit leads its voltage by 90° and average power consumption in pure capacitor is zero.(7 marks) 6 (b) A delta connected load having branch impedances of (15 +j20)Ω is connected to a220V, 3 phase AC supply. Find
(A) Line Currents
(B) Per phase power consumed
(C) What is the phasor sum of the line currents? Why does it have this value?
(7 marks)
7 (a) Explain construction of cable in detail.(7 marks) 7 (b) Short note on ELCB(7 marks)

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