Elements of Electrical Engineering - Jun 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. 1 (a) Explain effect of temperature on resistance(3 marks) 1 (b) Derive equivalent resistances for delta to star transformation. (6 marks) 1 (c) A 100 V, 100 W lamp is connected in series with a A 100 V, 60 W lamp across 200 V supply. Determine current drawn and power consumed by each lamp.(5 marks) 2 (a) Draw wiring diagram for staircase wiring.(3 marks) 2 (b) Derive expression for voltage across capacitor (vc) during charging of capacitor. (6 marks) 2 (c) Three capacitors having capacitances of 10 μF, 20 μF 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. (5 marks) 3 (a) State similarities between magnetic circuit and electrical circuit(4 marks) 3 (b) Explain self induced emf and mutually induced emf.(6 marks) 3 (c) 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.(4 marks) 4 (a) Define : (i) Frequency (ii) Average value (iii) power factor. (3 marks) 4 (b) Prove that current in pure inductive circuit lags its voltage by 90°(6 marks) 4 (c) Two currents are given by expression: i1=40 sin(314t+30°) and i2=20 sin(314t-60°). Find expression for (i1 - i2).(5 marks) 5 (a) Explain series resonance circuit. Draw resonance curve.(7 marks) 5 (b) A coil resistance 15Ω and inductance 0.05 H is connected in parallel with a non-inductive resistance of 20Ω. 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) Establish relation between line voltage & phase voltage and current relation in 3-phase star connection. Draw phasor diagram. (7 marks) 6 (b) Explain two wattmeter method for 3-phase power measurement(7 marks) 7 (a) State types of fuse and explain any one.(4 marks) 7 (b) Explain different types of lighting schemes.(5 marks) 7 (c) Explain construction of cable.(5 marks)