Guru Nanak Dev University 2007-2nd Sem B.Sc Chemistry MODERN PHYSICS (CHEM-205) (-2k7) - Question Paper

2057

B.Sc. (H.S.) in Chemistry, IInd Semester

MODERN PHYSICS

Paper : Chem-205

Time allowed : 3 Hours
Maximum Marks : 75

Note : The ques. paper is having 5 parts namely A, B, C, D and E. part A is compulsory. parts B, C, D and E have 2 ques. every and candidates are needed to attempt 1 from every part.


part - A
(1½ x 10 = 15)

1.

(a) What do you mean by wave group velocity ?

(b) elaborate photographic emulsions ?

(c) What is meant by the half-life time of a radioactive substance ?

(d) describe 1 Curie radioactivity.

(e) elaborate 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. elaborate the sideband frquenncies ?

(j) describe the barrier potential and barrier energy in jubction diode.


part - 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 provided 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 current in atomic nuclei ? presume an atomic nucleus is about five 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 one meV. (Given Planck's constant h = 6.6 x 10-36 Js). (4+5+6)

3. (a) discuss Planck's hypothesis of quantum theory of radiation and find the Planck's radiation formula.
(b) X-rays of wavelength 0.80 Å fall on a metal plate. obtain the wavelength associated with the emitted photoelectrons. presume negligible work function.


part - C

4. (a) discuss 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. explain the composite decay process and find the expressions for numbers of atoms current in the mixture at a specific time. (8+7)

5. discuss the principle, working, construction and applications of mass spectrograph. (15)


part - D

6. (a) define 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 needed to produce 1 ion-pair is 35 eV and chamber capacitance is 25 pF. (10+5)

7. (a) define the different intrinsic quantum numbers associated with elementary particles.
(b) refer to attachment. (10+5)


part - E

8. (a) elaborate voltage regulators ? discuss the action of a Zener voltage regulator with the help of a neat circuit diagram and explain its limitations.
(b) 2 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) discuss amplitude modulation and explain its limitations.
(c) In CRO 200V, 50Hz signal produces a deflection of 2cm corresponding to a certain setting of vertical gain control. If a different voltage produces 3cm deflection, what is the value of this voltage ? (5+6+4)

Earning:   Approval pending.