Basic Electricals & Electronics Engg. - May 2014

First Year Engineering (Set A) (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) Define voltage and current sources(2 marks) 1 (b) Distinguish between Dependent sources and Independent sources.(2 marks) 1 (c) How will you obtain the current through single phase load of 2 kW with PF = 0.8 at 230 Volts. Find active power, reactive power and apparent power for the given load.(3 marks)

Answer any one question from Q1. (d) or Q1. (e)

1 (d) Establish the physical meaning of reactive power with the help of necessary derivations.(7 marks) 1 (e) Distinguish between 3 phase balanced and unbalanced supply. What is the impact of unbalanced load on the power supply. (7 marks)

Answer the following with reference to single phase transformer:

2 (a) Justify with reason the constant flux in the core with variation in load connected to secondary terminal.(2 marks) 2 (b) Draw phasor diagram of single phase transformer for an inductive load. What variation is observed for a capacitive load? (2 marks) 2 (c) Specify the application of equivalent circuit?? (3 marks)

Answer any one question from Q2. (d) or Q2. (e)

2 (d) A 500 KVA transformer has 90% efficiency at full load and at 70% of full load both at upf.
(i) separate out the transformer losses.
(ii) Determine the transformer efficiency at 80% of full load , upf.(7 marks) 2 (e) A coil wound on an iron core is excited from an ac source at voltage V(rms). Derive the expression for maximum flux in the core. Why is it independent of the core reluctance.(7 marks) 3 (a) Draw the construction of 3 phase induction machine and synchronous machine.(2 marks) 3 (b) Develop the emf equation for a 3 phase induction motor.(2 marks) 3 (c) Draw the torque slip characteristics of an induction motor. Develop necessary condition for maximum torque. (3 marks)

Answer any one question from Q3. (d) or Q3. (e)

3 (d) Classify DC machines and explain them briefly.(7 marks) 3 (e) A series motor runs at 600 rpm when taking a current of 110 A from a 230 volt supply. The useful flux per pole for 110 A is 24 mWb and that for 50 A is 16 mWb. The armature resistance and series field resistance are 0.12 ohms and 0.03 ohms respectively. Calculate the speed when the current has fallen to 50 A.(7 marks) 4 (a) Specify Different number systems used in digital electronics. What are floating numbers.(2 marks) 4 (b) State De-Morgan's theorem with example.(2 marks) 4 (c) Draw the truth table of JK flip-flop along with its logic diagram.(3 marks)

Answer any one question from Q4. (d) or Q4 (e)

4 (d) Explain the operation of half adder and full adder along with their logic diagram and truth table. Also deduce a full adder using EX-OR gate.(7 marks) 4 (e) Convert the following indicating the steps involved.
(i) (657)₀=(?)₁₀
(ii) (1D53)₁₆=(?)₁₀
(iii) (131,F2)₁₆=(?)₁₀(7 marks) 5 (a) Which is the transistor configuration for amplifier and why ? (2 marks) 5 (b) Why Silicon is usually preferred over germanium for fabrication semiconductor devices.(2 marks) 5 (c) Explain V-I characteristics and applications of Zener diode.(3 marks)

Answer any one question from Q5. (d) or Q5 (e)

5 (d) Explain the difference between avalanche multiplication and Zener breakdown.(7 marks) 5 (e) What are clipper and circuits. Given one example for each. How p-n junction is used as rectifier.(7 marks)