Subject Code QDB-43
PHYSICS (Main Examination) (English Medium)
Time 3 Hours Total Marks 200
Instructions The question paper has been divided into three parts, B and C. The number of questions to be attempted and their marks are indicated in each part.

Answers of all the questions of each part should be written continuously in the answer sheet and should not be mixed with other parts' Answer. In the event of answer found, which are belongs to other part, such answers will not be assessed by examiner.


The candidate should write the answer within the limit of words prescribed in the parts B and C.


If there is any difference in English language question and its Gujarati Translation, then English language question will be considered as valid.


Answer should be written in one of the two languages. Write in the language (English or Gujarati) preference given by you. Answer should not be written in both the languages in the same paper.


Part-A Instructions Question No. 1 to 20.

Attempt all 20 questions.


Each question carries 2 marks.


Answer should be given approximately in 20 to 30 words.


1. What do the magnitude and direction of a gradient of a scalar field represent

2. Give the conditions for a vector field V to be irrotational solenoidal.

3. In two body problem, what is reduced mass of the system What is its importance Why

is it called reduced mass

4.
One mole of a gas at 27 °C expands isothermally to a volume four times that of its initial

volume. Find the change in its entropy.

5.
Write Clausius and Kelvin-Planck's statements of second law of thermodynamics.

6.
When does the Hamiltonian of the system become equal to the total energy of the system

7.
In free expansion of an ideal gas the temperature of the ideal gas does not change and heat

is not added to the system. What happens to entropy of the system Explain.

8.
What is the condition for an ensemble to be stationary What can be said about average value of any physical quantity for such ensemble

9.
Explain ergodic hypothesis.

10.
Calculate the time required by a charged particle of mass m and charge q to travel a semicircle inside a dee in a cyclotron.

11.
In the photoelectric effect, when will the stopping potential be zero

12.
What are the admissibility conditions or requirements on the wave function

13.
What is the general condition for the eigenvalues of an operator to be real

14.
Calculate the resonance frequency of an LCR parallel resonant circuit with L 10 mH, C 1µF and R 1 O.

15.
What is the importance of the Poynting vector Give its expression in terms of electric field and magnetic field.

16.
Mention the special characteristics of a LASER.

17.
Find the minimum number of lines in a plane diffraction grating required to just resolve the sodium doublet. (5800 Å and 5895.9 in the second order.

18.
What is Skin Effect

19.
Give the statements of De Morgan's two theorems in context of boolean algebra and verify them using truth tables.

20.
Define Young modulus and bulk modulus. Write their formulae and SI units.


Part-B Instructions Question No. 21 to 32.

Attempt all 12 questions.


Each question carries 5 marks.


Answer should be given approximately in 50 to 60 words.


.
.
21.
Calculate the curl of the vector function V x2 .x 3xz2y . -2xzz .

22.
What are holonomic and non-holonomic constraints

23.
Normalize the one dimensional wave function . defined as


. Ae-ax for x 0
Aeax for x 0
24.
Describe the construction and working of Geiger-Muller counter.

25.
An archeologist excavates a piece of wood of mass 100 gm from an excavation site. The wood shows a 14C activity of 750 disintegration per minute. Assuming that a living tree shows a 14C activity of 15 disintegration per gram per minute, estimate the age of the piece of wood. Half-life of 14C is 5730 years and ln 2 0.693.

26.
What were the problems with beta decay that led Pauli to propose neutrino

27.
Find the kinetic energy of an electron whose de Broglie wavelength is the same as wavelength of a 100 keV X-ray.

28.
What is the limit of resolution of optical instrument Explain Rayleigh criterion of resolution.

29.
A capacitor C and resistor R are connected in series to a battery having emf e 12 V. If C 5.00 µF and R 8.00 × 105O, find the time constant of the circuit, the maximum charge on the capacitor, the maximum current in the circuit and the charge as functions of time.

30.
The distance between adjacent atomic planes in a crystal is 1.2 nm. Find the angle of diffraction for fourth order for 0.3 nm X-rays.

31.
Explain the gain of negative voltage feedback amplifier with a neat diagram.

32.
What are conditions for Coulomb gauge and Lorentz gauge What are their advantages


Part-C Instructions Question No. 33 to 39.

Attempt any 5 out of 7 questions.


Each question carries 20 marks.


Answer should be given approximately in 200 words.


33.
What was the aim of Michelson-Morley experiment What was the ultimate result found out Describe the experiment with necessary steps.

34.
Obtain Schrodinger wave equation for a simple harmonic oscillator. Solve the equation and discuss the results.

35.
What are the problems with Ampere's law How did Maxwell correct it

36.
Discuss in detail Fermi theory and Gamow's explanation of ß-decay.

37.
Explain Joule-Thomson process of cooling. Derive the expression for Joule-Thomson cooling.

38.
Draw the circuit of Maxwell's bridge and describe how it can be used to measure inductance.

39.
Derive expressions for Einstein coefficients and the relation among them.