BALOCHISTAN PUBLIC SERVICE COMMISSION
COMPETITIVE EXAMINATION 2021
FOR RECRUITMENT TO THE POSTS OF
ASSISTANT COMMISSIONER/SECTION OFFICER (B-17)
IN THE SERVICES & GENERAL ADMINISTRATION DEPARTMENT
PHYSICS
Total Marks: 150 July 02, 2021 Time Allowed: 03 Hours
NOTE: i Attempt any five questions. All questions carry equal marks.
ii All the parts (if any) of each Question must be attempted at one place instead of at different places.
iii Candidate must write Q No in the Answer Book in accordance with Q No in the Q Paper.
iv No Page/Space be left blank between the answers. All the blank pages of Answer Book must be crossed.
v Extra attempt of any question or any part of the attempted question will not be considered.
Q No 1 a) Explain curl and divergence of vector fields with their physical significance? Is divergence theorem applicable for each surface integrals? (10)
b) Vectors A and B have magnitudes of 5 units and 4 units, respectively. What is the angle between the directions of A and B if A.B is equal to (i) zero (ii) 12 units and (iii) -20 units? (10)
c) Find the angle between: (10)
(i) A = 2i + 2j – 4k and B = 2i – j + k
(ii) A = 4i – 2j + 4k and B = 3i – 6j – 2k
Q No 2 a) Describe Maxwell’s equations in differential and integral form. Explain significance of each equation. (10)
b) Describe power in A.C circuit. What is maximum power transfer theorem in AC? (10)
c) RLC series circuit connected to an AC voltage source with rms value of 50 volt. At half the resonant frequency, the phase angle is 28 degree, the inductive reactance is 50 Ohm. What is the average dissipated power at twice the resonant frequency in Watt? (10)
Q No 3 a) Distinguish between linear and angular momentum. Explain the law of conservation angular momentum with suitable examples. (10)
b) What is moment of inertia? State and prove parallel axis theorem. (10)
c) What is vector triple product? Show that A × (B × C) = (A . C) B – (A . B) C. (10)
Q No 4 a) What are adiabatic and isothermal changes? Explain with volume pressure diagram. Why is the curve of an isothermal process above that of an adiabatic process during compression? (10)
b) How do you find the internal energy of a state equation? How to solve constants out of the internal energy equation? (10)
c) Calculate the volume of 1 mole of an ideal gas at STP. (10)
Q No 5 a) What is Compton Effect? Derive an expression for Compton shift. How it depends upon the scattering angle? What do you mean by free limit? (10)
b) How can photons have no mass and yet still have energy given that E=mc²? Also Derive the relation between relativistic energy with momentum. (10)
c) Why is speed of light independent of frame of reference? Show that speed of light is independent of the relative motion between frames of reference. (10)
Q No 6 a) Derive an expression for capacitance of cylindrical and spherical capacitor. (10)
b) Describe phenomenon of diffraction of X-rays through crystals also explain their applications. (10)
c) In a double-slit experiment, the distance between slits is 5.0 mm and the slits are 1.0 m from the screen. Two interference patterns can be seen on the screen: one due to light of wavelength 480 nm, and the other due to light of wavelength 600 nm. What is the separation on the screen between the third-order (m = 3) bright fringes of the two interference patterns? (10)
Q No 7 a) Define Entropy. State second law of thermodynamics in terms of entropy. (10)
b) What is a steady flow? Describe What is the Poiseuille method? How steady flow of fluid through a capillary tube was studied by Poiseuille. (10)
c) How do you calculate the mass of the Sun using Kepler’s third law? Using Kepler’s law calculate mass of the sun if the earth period is 3.16 × 10^7 s and its orbital radius is 1.5 × 10^11 m. (10)
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