Federal Public Service Commission (FPSC)
Competitive Examination for Recruitment to BPS-17 Posts under the Federal Government
Paper: Physics
Time Allowed: 3 Hours
PAPER-I (Subjective) 80 Marks
PART-II
Attempt ONLY FOUR questions from PART-II, ALL Questions carry EQUAL marks.
Q. No. 2. (a) Define a Scalar Field. Obtain an expression for the Gradient of a Scalar Field. Why is the Gradient of a Scalar Field a Vector? (11)
(b) Given ϕ(x, y, z) = x²yz³, find grad ϕ at (1, 2, 1). (5)
(c) For what value of ‘a’ are the vectors
A = 2i + aj + k
and
B = 4i − 2j − 2k
perpendicular? (4)
Q. No. 3.
(a) Distinguish between Linear and Angular Momentum. Explain the Law of Conservation of Angular Momentum. Prove that Angular Momentum remains constant in the absence of external torque. (13)
(b) The angular momentum of a particle is given by:
J = 8t⁴i − 2t²j + 12t³k
Find the torque τ at t = 1. (7)
Q. No. 4.
(a) Show that the work done by a constant force is equal to the difference between the initial and final kinetic energies of a body. (10)
(b) Prove that the total work done by a conservative force around a closed path is ZERO and is independent of the path. (10)
Q. No. 5.
(a) Describe Einstein’s Postulates of the Special Theory of Relativity. (10)
(b) Establish the Mass–Energy relationship. (6)
(c) What is the speed of an aircraft whose clock runs one second slow per hour relative to a clock on the Earth?
[Given: c = 3 × 10⁸ m/s] (4)
Q. No. 6.
(a) Distinguish between Streamline and Turbulent Motion of a Liquid. (3)
(b) What is Coefficient of Viscosity? Explain in detail Stoke’s Law applicable in determining the coefficient of viscosity of a viscous liquid experimentally. (14)
(c) Why do automobile manufacturers recommend using different viscosities of engine oil in cold and hot climates? (3)
Q. No. 7.
(a) Define Entropy. State the Second Law of Thermodynamics in terms of entropy. (13)
(b) Show that entropy remains constant in a reversible process but increases in an irreversible one. (3)
(c) Distinguish between Isothermal and Adiabatic Processes. (4)
Q. No. 8.
(a) Explain the phenomenon of diffraction from a Single Slit and a Diffraction Grating. Discuss the conditions for maxima and minima in both cases. (14)
(b) Differentiate between Fresnel and Fraunhofer Diffraction. (6)
PAPER-II (Subjective) 80 Marks
PART-II
Attempt ONLY FOUR questions from PART-II, ALL Questions carry EQUAL marks.
Q. No. 2.
(a) A non-conducting disk of radius R has a uniform positive surface charge density σ. Find the electric field at a point along the axis of the disk at a distance x from its center. Assume that x is positive. (9)
(b) Explain the use of dielectric materials between the conducting plates of a capacitor. (6)
(c) The parallel plates of a 1.0 F capacitor are 1.0 mm apart. What is their area? (5)
Q. No. 3.
(a) Explain the working mechanism of the Moving Coil Microphone and Electric Guitar. (3+3)
(b) Explain the working mechanism of the Ground Fault Circuit Interrupter (GFCI) and Walk-through Metal Detector. (3+3)
(c) An observer is 1.8 m from a light source (whose dimensions are much smaller than 1.8 m) with a power output of 250 W. Calculate the RMS value of the electric field at the observer’s position. Assume the source radiates uniformly in all directions. (8)
Q. No. 4.
(a) Enlist the practical applications of the diode. (5)
(b) Explain the Volt–Ampere characteristics of the diode. (6)
(c) Differentiate between Insulators, Conductors, and Semiconductors using the Energy Band Gap approach. (9)
Q. No. 5.
(a) State and explain Amplitude Modulation (AM) in communication systems. (8)
(b) Explain the construction of a PNP transistor and describe one of its practical applications in detail. (4+4)
(c) What are the advantages of digital signals over analog signals? (4)
Q. No. 6.
(a) Explain the Lyman, Balmer, and Paschen series of atomic hydrogen. (3+3+3)
(b) State and explain the Photoelectric Effect. (5)
(c) Some major features of the Photoelectric Effect cannot be explained by the classical wave theory of light. Discuss in detail. (6)
Q. No. 7.
(a) Explain the Zeeman Effect with the help of an energy level diagram. (8)
(b) Explain the dual nature of light. (4)
(c) State and explain Heisenberg’s Uncertainty Principle. (8)
Q. No. 8.
(a) Explain the working mechanism of the Scintillation Counter and Bubble Chamber in detail. (4+4)
(b) State and explain Nuclear Fission, giving at least three examples. (6)
(c) A small cyclotron of maximum radius R = 0.25 m accelerates protons in a magnetic field of 1.7 T. Calculate:
(i) The frequency required for the applied alternating voltage.
(ii) The kinetic energy of the protons when they leave the cyclotron. (6)
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