Basic Electrical and Electronic Engineering - May 2013

AU First Year Engineering (Semester 2)

Total marks: --
Total time: --

INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary.

1 A 120 ? resistor has a specified maximum power dissipation of 1W. Calculate the maximum current level. 2 marks

2 Three inductive coils each with resistance of 15? and an inductance of 0.03 H are connected in star to a 3? 400 V, 50 Hz supply. Calculate the phase voltages. 2 marks

3 A dc shunt generator supplies a load of 10 kW at 220 V through feeders of resistance 0.1?, The resistance of armature and shunt field windings is 0.05? and 100 ? respectively. Calculate the terminal voltage. 2 marks

4 In a single phase transformer, N_p=350 turns, N_s=1050 turns, E_p=400 V. Find E_g. 2 marks

5 Write any two salient points on a p-n junction. 2 marks

6 When should a transistor be biased? Name two common biasing circuits. 2 marks

7 Find the following binary difference:
1011010-0101110 2 marks

8 An active high S-R latch has a '1' on the S-input and 'o' on the 'R' input. What state is the latch in? 2 marks

9 As related to amplitude modulation, what is overmodulation, undermodulation and 100% modulation? 2 marks

10 Why are digital signals said to be noise immune? 2 marks

Answer any one question from Q11 (a) & Q11 (b)

11 (a) (i) A sinusoidal current wave is given by i=50 sin (100 ?t). Determine the root mean square value. 4marks

11 (a) (ii) Write short notes on moving Iron Measuring Instruments under the following headings:
(1) Operating principle
(2) Classification
(3) Advantages and disadvantages. 8 marks

11 (b) (i) 3?, 200 kW, 50 Hz delta connected induction motor is supplied from a 3?, 400 V, 50 Hz supply system. The efficiency and power factor of 3? induction motor are 91% and 0.86 respectively. Calculate:
(1) (A) Current in each motor phse
(B) Line current
(2) Phasor diagram of the circuit 8marks

11 (b) (ii) Find the current in the 8? resistor in the following circuit using Kirchoff's laws.

8 marks

Answer any one question from Q12 (a) & Q12 (b)

12 (a) (ii) With neat diagrams explain the construction and principle of operation of a single phase transformer. What are the characteristics of an ideal transformer? 8 marks

12 (b) (i) Explain the basic nature of the emf induced in the armature of a d.c. machine. 4 marks

12 (b) (i) How can the alternating current waveform in the armature be converted into a dc waveform? 4 marks

12 (b) (ii) A 200 V dc shunt motor takes a total current of 100 A and runs at 750 rpm. The resistance of the armature winding and of shunt field winding is 0.1 and 40? respectively. Find the torque developed by the armature. 8 marks

Answer any one question from Q13 (a) & Q13 (b)

13 (a) (ii) Using the two diode analogy explain why the base-emitter junction has to be forward biased to provide collector current. 4 marks

13 (a) (ii) Sketch a common emitter amplifier circuit with an NPN transistor. 4 marks

13 (b) (i) Explain the avalanche effect that accounts for the reverse breakdown voltage (PIV) of a diode. 4 marks

13 (b) (i) What is the effect on capacitance of a PN junction diode as forward and reverse bias are applied? 4 marks

13 (b) (ii) Explain the amplifying action of a transistor. 6 marks

13 (b) (ii) In a CE I_B changes from 100 ?A to 150 ?A which causes a change in I_C from 5mA to 7.5 mA. If V_CE is held constant at 10 V, find ?_ac (h_fc) 2 marks

Answer any one question from Q14 (a) & Q14 (b)

14 (a) (i) Realise the give expession using only NAND gates and inverters:
xyz+x'y'z 4 marks

14 (a) (ii) Design a full adder, construct the truth table, simplify the output equations and draw the logic diagram. 8 marks

14 (b) (i) Draw the logic diagram for a four bit parallel input parallel output register. Indicate inputs, outputs and a negative edge trigerred clock. 4 marks

14 (b) (i) Draw a simple ring counter and briefly describe its counting action. 4 marks

14 (b) (ii) Give a brief explanation of an A/D conversion and the need for the A/D conversions. 4 marks

14 (b) (ii) Convert 95.0625₁₀ to binary. 4 marks

Answer any one question from Q15 (a) & Q15 (b)

15 (a) (ii) What is the need for modulation? Explain the principles behind amplitude modulation and frequency modulation. Compare and contrast the two types of modulation. 10 marks

15 (b) (i) With neat diagrams explain any one method of amplitude modulation and its corresponding demodulation. 8 marks

15 (b) (ii) Write short notes on the following modes of communication:
(1) Microwave
(2) Optical fibre 8 marks