# Electric Circuit and Electron Devices 2nd MJ12 EC2151

Question paper code:99550
B.E./B.Tech. DEGREE EXAMINATION, MAY/JUNE 2012.
Second Semester
Electronics and Communication Engineering
EC 2151/147201/EC 25/10144 EC 205/080290007/EE 1152 ELECTRIC CIRCUITS AND ELECTRON DEVICES
(Common to Computer Science and Engineering, Information Technology, Biomedical Engineering and Medical Electronics branches)
(Regulation 2008)

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PART A(10*2 = 20 marks)

1. What is the equivalent capacitance when several capacitances C1, C2,...are connected (a) in series and (b) in parallel ?
2. State Thevenins theorem.
3. Find the time constant of a RL circuit having R = 10 ohms and L = 1 milli Henry.
4. What are tuned circuits? Give an application.
5. Define barrier potential in a PN junction diode.
6. What is avalanche breakdown?
7. Why collector region of a transistor is larger in area than emitter region?
8. What is pinch off voltage of a JFET?
9. Write the expression for intrinsic stand off ratio for UJT.
10. What are the materials used in LEDs?

PART B(5*16 = 80 marks)

11. (a) (i) Write the mesh equations for the circuit shown below. (6 marks)
(ii) Determine the output voltage Vout in the circuit shown below. (10 marks)

OR

(b) (i) What are called Dual Networks? Obtain the Dual Network of the following circuit. (6 marks)
(ii) Obtain Thevenins equivalent of network shown below. (10 marks)

12. (a) A resistance R, a capacitance C and an inductance L of 0.5 H are connected in series. When a voltage of V = 350 cos (3000t-20degree) volts is applied to this circuit, the current flowing is 15 cos (3000t-60degree) ampere. Find the values of R and C. (16 marks)

OR

(b) (i) The signal voltage in the circuit shown below is
what should be the value of C in order that the circuit would resonate at this signal frequency? At this condition, find the values of I, Vc, Q and bandwidth of the circuit. (10 marks)
(ii) (RL + j20)ohm and (20-j10)ohm are connected in parallel. Determine the value of RL for resonance. (6 marks)

13. (a) (i) With neat sketches, describe the construction and working of PN junction semiconductor. What is depletion layer? Explain the motion of electrons or holes of PN junction in forward and reverse biased mode. Also explain the V-I characteristics for these bias conditions. (12 marks)
(ii) Differentiate between intrinsic and extrinsic semiconductors. (4 marks)

OR

(b) (i) Explain what are means by transition capacitance and diffusion capacitance in diode. (6 marks)
(ii) What is the speciality of Zener diode? (4 marks)
(iii) Discuss the V-I characteristics of Zener diode with a suitable diagram. (6 marks)

14. (a) (i) Draw the circuits for the CE, CB and CC configurations of a bipolar junction transistor. (6 marks)
(ii) For the common emitter configuration, draw the circuit and explain the input and output characteristics. (10 marks)

OR

(b) (i) Sketch and explain the construction of N-channel enhancement type MOSFET. Give also its symbol. (4 marks)
(ii) Describe, with suitable sketches, the operation and characteristics (transfer, drain) of the N-channel enhancement-type MOSFET. (8 marks)
(iii) Explain briefly the effect of temperature on MOSFET. (4 marks)

15. (a) (i) Describe the construction, the symbol, V-I characteristics and applications for Tunnel diode. (8 marks)
(ii) With the help of two transistor equivalent model, explain the working of SCR. Also explain the regenerative action that takes place in SCR. (8 marks)

OR

(b) Explain the construction symbol and characteristics of
(i) photovoltaic cell. (8 marks)
(ii) phototransistor. (8 marks