# 2005 Madras University B Sc Electronics ELECTRICITY AND BASIC ELECTRONICS Question paper

** University Question Papers **

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**2005 Madras University B Sc Electronics ELECTRICITY AND BASIC ELECTRONICS Question paper

ELECTRICITY AND BASIC ELECTRONICS

NOVEMBER 2005 PJ1A

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Time :Three hours Maximum : 100 marks

PART A-(10x3=30 marks)

Answer any Ten questions.

All question carry equal marks.

1. A certain charge Q is divided into two parts q and Q–q. How the charges Q and q must be related so that when experience maximum electrostatic repulsion.

2. Find out the pints where (a) V=0 and (b) E=0 in the following figure:

p +q -3q

r 1m

3. What is the energy of the charged conductor (a) interms of charge and capacitance (b) potential and capacitance and (c) charge and potential ?

4. Find the capacitance of the system of three parallel plates each of area Am2 , separated by d1 and d2 metres. The space between them is filled with dielectricsof relative dielectric constants ?1 and ?2 (The dielectric of free space is ?0 )

A ?1 ?2

d1 d2

5.Show that for maximum current, the cells should be connected in mixed grouping with external resistance is equal to the net internal resistance .

6. What is the principle of potentiometer?

7. Draw circuit diagram of bridge rectifier and what are its advantages and disadvantages.

8. What is the purpose of clipper and clamper? How clipping at two different levels can be made?

9. Compare the performance of common-emitter, common collector and common base transistor amplifiers.

10.State Thevenins theorem and prove it in case of two terminal network.

11. Draw the symbols for (a) AND gate (b) OR gate and (c)NOT gate . Give its truth table.

12. A current of 1 A is flowing in the sides of an equilateral triangle of side 4.5x10-2 m. Find the magnetic field at the centroid of the triangle.

PART B-(5x6=30 marks)

Answer any FIVE questions.

All question carry equal marks.

13. Derive a relation for the potential at any point P due to an uniformly charged disc.

14. Describe the quadrant electrometer. How ionization current can be measured with it.

15. Derive a relation for torque on a current loop in a uniform magnetic field.

16. Compare the L-section or inductor input filter with that of the p-section or capacitor input filter.

17. Explain the response of high pass RC circuit to (a) sinusoidal input (b) square wave input and (c) exponential input.

18. Using the method of electrical images, determine the surface density of induced or polarized charge on a dielectric slab of infinite face in front of a point charge.

19. Calculate the voltage gain of a CE amplifier from the following data :

hf =100, RL =15K?, hi=60 K?, and ?h=12.

PART C-(4x10=40 marks)

Answer any FOUR questions.

All question carry equal marks.

20. Derive a relation for the electrostatic energy of a charged sphere.

21. Show that there is always a loss of energy on charges between two condensers.

22. Describe with necessary theory the method of measuring the low resistance using a Carey Foster’s bridge.

23. Describe a P-N junction full wave rectifier. Derive relation for its efficiency. What is its ripple factor?

24. Obtain expressions for the current gain, voltage gain, input impedance and output impedance and output impedance in terms of hybrid parameters for Ce amplifier.

25. The mid frequency gain of an RC coupled amplifier is 200. The value of the lower and upper cut-off frequencies are fL =50Hz and fH =100kHz.Find the frequencies at which the gain is reduced to 150.