Ex/FP/2/XIV/78/2012

BACHELOR OF SCIENCE FINAL EXAMINATION, 2012( 2nd Semester )

PHYSICS (HONOURS)PAPER : H-14

Time : Two Hours Full Marks - 50

Use Separate Answer-Script for each Group

(25 marks for each Group)

Group - A

Answer any Five questions

1. a) Draw a common collector amplifier circuit with

potential divider biasing network and explain its

operation.

b) For a small-signal equivalent circuit of a common

collector amplifier ie Lh R 4k= = Ω and feh 100= .

Find the input resistance and voltage gain.

( )re oeh h O≈; . 2+3

2. a) What is a Darlington pair? Describe the function of a

Darlington pair in CC-CC configuration.

b) Explain briefly the function of a simple series voltage

regulator using a transistor and a zener diode. 3+2

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b) Can we describe a photon in the framework of

relativity?

c) A particle of mass 'M' decays into two pieces, each of

mass 'm' what is the speed of each piece as it flies off?

Discuss the threshold of the process. 5+2+3

11. Write short notes : (any two) 5+5

i) Neutrino oscillation.

ii) The Two fluid model for superfluidity.

iii) Landou theory of phase transition.

iv) Quark model for hadrons.

- 4 -

- 2 - - 3 -

3. a) Draw a circuit diagram of a class-B push-pull amplifier

and deduce its maximum efficiency.

b) What is cross-over distortion? 4+1

4. a) Obtain expression for the voltage gain of on RC-

coupled amplifier in low frequency range?

b) The mid-frequency gain of an RC-coupled amplifier is

100. Its 3 dB frequencies are 50Hz and 200 KHz. At

what frequencies is the gain 80? 3+2

5. a) What is pinch off voltage in a JFET? Explain how it

can be found out from (i) output characteristic curve

and (ii) mutual characteristic curve.

b) An n-channel JFET has IDSS = 12 mA. If the

transconductance gm at VGS = 0 is 4 millimho, find the

'pinch off' voltage. 3+2

6. a) State and explain Barkhavsen's criteria for sustained

oscillation.

b) Draw a schematic circuit diagram of a colpitt oscillator

and calculate its frequencies of oscillation. 1+4

7. a) How is the bandwidth of an RC-coupled amplifier

modified when negative feedback is used?

b) A RC-coupled amplifier has mid-frequency gain of

100 and a bandwidth of 20 KHz. If the amplifier is

now provided with a negative feedback network with

|B| = 0.02, what would be the new bandwidth? 3+2

Group - B

Answer Q. No.8 and any Two from the rest.

8. a) Draw Feynman diagram for Bhaba scattering.

b) How does a neutrino differ from an antineutrino.

c) Deuteron cannot exist in 3D1 state - explain.

d) Write down the quark structure for P, n, ∧ particles.

e) What is Josephson effect? 1+1+1+1+1

9. a) Discuss the BCS theory of superconductivity. What is

Meissner effect? 5+5

b) Deduce London equation for a superconductor and

discuss the physical interpretion of the equation.

10. a) Distinguish between classical collision and relativistic

collisions of different type stating the relevant

conservation laws.

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