Physics (Honours) (H 14)
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Transcript of Physics (Honours) (H 14)
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
[ Turn over
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.
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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.
[ Turn over