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Posted By: Manav Member Level: Gold Posted Date: 10 Jan 2008
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2007 Guru Nanak Dev University B.Sc Chemistry MODERN PHYSICS (CHEM-205) 2nd Sem (MAY-2k7) Question paper
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2057
B.Sc. (H.S.) in Chemistry, IInd Semester
MODERN PHYSICS
Paper : Chem-205
Time allowed : Three Hours
Maximum Marks : 75
Note : The question paper is having FIVE sections namely A, B, C, D and E. Section A is compulsory. Sections B, C, D and E have TWO questions each and candidates are required to attempt ONE from each Section.
SECTION - A
(1½ x 10 = 15)
1.
(a) What do you mean by wave group velocity ?
(b) What are photographic emulsions ?
(c) What is meant by the half-life time of a radioactive substance ?
(d) Define one Curie radioactivity.
(e) What are radiation doses and their units ?
(f) What do you mean by the stable elementary particles ane their resonances ?
(g) What is the practical importance of voltage regulation in power supplies ?
(h) What is modulation factor ?
(i) An audio signal of 1KHz is used to modulate a carrier of frequency 500 KHz. What are the sideband frquenncies ?
(j) Define the barrier potential and barrier energy in jubction diode.
SECTION - B
2. (a) Deduce the Bragg's condition for diffracted X-Rays from a set of crystal planes.
(b) Show that wavelength associated with electrons accelerated through a potential difference of V volts is given by : h/v2meV
where h is the Planck's constant, m is the rest mass of electron and e its charge.
(c) Apply uncertainty principle to investigate whether electrons are present in atomic nuclei ? Assume an atomic nucleus is about 5 x 10-15 (10 raised to power -15) m in radius and the energy of a ß-particle emitted from nucleus is of the order of 1 meV. (Given Planck's constant h = 6.6 x 10-36 Js). (4+5+6)
3. (a) Explain Planck's hypothesis of quantum theory of radiation and obtain the Planck's radiation formula.
(b) X-rays of wavelength 0.80 Å fall on a metal plate. Find the wavelength associated with the emitted photoelectrons. Assume negligible work function.
SECTION - C
4. (a) Explain the mean-life of a radioactive substanc. Show that the mean life of an atom of a radioactive substance is reciprocal of its decay constant.
(b) A nucleus 'A' decays into 'B' with half life T1 and 'B' decays into 'C' with half life T2. Discuss the composite decay process and obtain the expressions for numbers of atoms present in the mixture at a specific time. (8+7)
5. Explain the principle, working, construction and applications of mass spectrograph. (15)
SECTION - D
6. (a) Describe the principle, construction and working of cloud chamber. How it can be used to measure the energy of a charged particle ?
(b) An a-particle of energy 4.2 MeV is completely stopped in an ionization chamber. What is the pulse voltage and current in an external resistance of 10nO (n=6), if energy required to produce one ion-pair is 35 eV and chamber capacitance is 25 pF. (10+5)
7. (a) Describe the various intrinsic quantum numbers associated with elementary particles.
(b) refer to attachment. (10+5)
SECTION - E
8. (a) What are voltage regulators ? Explain the action of a Zener voltage regulator with the help of a neat circuit diagram and discuss its limitations.
(b) Two power supplies (say 'A' and 'B') are available. No-load voltage and full-load voltage of 'A' are 30V and 25V respectively, whereas for 'B' these values are 30V and 29V. Which is better power supply and why ? (10+5)
9. (a) What is modulation ? Why is modulatiom necessary in communication system ?
(b) Explain amplitude modulation and discuss its limitations.
(c) In CRO 200V, 50Hz signal produces a deflection of 2cm corresponding to a certain setting of vertical gain control. If another voltage produces 3cm deflection, what is the value of this voltage ? (5+6+4)
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