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) What is the cross product of two vectors? Why is the cross product called a pseudo vector? (b) What is divergence of a vector field? What is its physical significance? (c) What is line integral? Under what condition is it used to calculate the work done? (d) Consider three vectors:
Q. No. 3.
(a) What do you mean by circular motion? What is centrifugal force? Explain your answer by taking an example from daily life.
(b) What is projectile motion? Why does a cricket player lower his hand while catching a ball?
(c) What do you mean by work done by the system and work done on the system? Explain by taking an example of each.
(d) A batsman hits a cricket ball at an angle with respect to the horizontal. The ball would strike the ground at a distance of 60 m from the batsman if it is not stopped. But a fielder at a distance of 55 m catches the ball at a height of 1.5 m. Calculate the angle of projection and the velocity of projection.
Q. No. 4.
(a) What do you mean by phase velocity and group velocity? Derive the relation between group velocity and phase velocity.
(b) What is the superposition of waves? Show that standing waves are produced by the superposition of two waves of equal amplitudes moving in opposite directions.
(c) A medium is disturbed by an oscillation described by:
Y = 3.0 cm sin(πx/10 cm) cos(50πt)
Determine the amplitude, frequency, wavelength, speed and direction of the component waves whose superposition produces this result.
(d) If light of wavelength λ = 660 nm has a wave train of 20λ, what are its coherence length and coherence time?
Q. No. 5.
(a) What is unique about light from a laser source, and why should you never look directly into a laser beam? Explain briefly.
(b) What is plasma? What do you mean by plasma frequency? Briefly discuss.
(c) How is the blue laser useful in storing a large amount of data on a CD as compared to a red laser?
(d) For the He-Ne laser, at distances of 2 m and 4 m from the laser, the output beam spot diameters are 2 mm and 3 mm. Calculate the angle of divergence.
Q. No. 6.
(a) What is viscosity? Discuss the effect of temperature on the viscosity of liquids and gases.
(b) Differentiate between streamline flow and turbulent flow. Establish the equation of continuity.
(c) Explain why the level of mercury falls in a capillary tube placed in a container of mercury, while it rises in a capillary tube placed in water.
(d) A garden hose has an inside diameter of 2 cm and water flows through it at 3 m/s.
(i) What nozzle diameter is required for the water to emerge at 10 m/s?
(ii) At what rate does the water leave the nozzle?
Q. No. 7.
(a) What do you understand by classical statistical mechanics and quantum statistical mechanics?
(b) Differentiate between Fermi-Dirac, Bose-Einstein and Maxwell-Boltzmann statistics.
(c) What is the equipartition of energy? Explain.
(d) A 0.5 m³ vessel is filled with air at atmospheric pressure. The air is churned by a paddle wheel attached to a shaft of 0.1 m diameter, rotating at a speed of 1800 rpm. A force of 5.0 N acts on the rim of the shaft. What would be the pressure in the vessel after 10 seconds of operation?
Q. No. 8.
Write notes on any FOUR of the following:
(a) Polarization of light and its application in determining the specific rotation of a liquid.
(b) Wave equation on a string.
(c) Normal and anomalous dispersion of light.
(d) Kinetic theory of gases.
(e) Scalar Triple Product.
PAPER-II (Subjective) 80 Marks
PART-II
Attempt ONLY FOUR questions from PART-II, ALL Questions carry EQUAL marks.
Q. No. 2
(a) What is dipole moment? Obtain the expression for the potential and field due to an electric dipole. (10)
(b) Calculate the potential at a point on the axis of a circular plastic disk of radius R, one surface of which carries a uniform charge density σ. (8)
(c) Why do we use the unit “electron volt”? (2) (20)
Q. No. 3.
(a) State and explain the Biot-Savart law. (4)
(b) State and prove Ampere’s law. Apply it to calculate the magnetic field due to a solenoid. (10)
(c) A long straight wire carries a current of 20 amperes. An electron at 2.0 cm from the wire is travelling at a speed of 10⁷ m/sec. What force acts on the electron if its motion is directed: (i) Towards the wire (ii) Parallel to the wire (iii) At right angles to the direction given in (i) and (ii). (6) (20)
Q. No. 4.
(a) Write Maxwell’s equations and explain the significance of each equation. (6)
(b) Deduce Maxwell’s equations for free space and also prove that electromagnetic waves are transverse. (12)
(c) What is index of refraction? (2) (20)
Q. No. 5.
(a) Describe the Stern-Gerlach experiment that provided experimental evidence of the space quantization of atomic magnetic moments. (10)
(b) What is the physical significance of the three quantum numbers n, l, and m in the labelling of the hydrogenic wave functions? (6)
(c) What do you understand by strange particles? (4) (20)
Q. No. 6.
(a) What is the liquid drop model of the nucleus? Write down its essential features. (8)
(b) What are magic numbers? How can they be generated on the basis of shell model? (8)
(c) What is nuclear fusion? (4) (20)
Q. No. 7.
(a) Differentiate Metals, Semiconductors and Insulators on the basis of Energy Band Theory. (6)
(b) What is a rectifier? How can we use a diode as a rectifier? Explain half-wave rectification in detail with diagrams. (14) (20)
Q. No. 8.
Write short notes on any TWO of the following: (10 each)
