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 (Objective) 20 Marks
PART-I
Q. No. 1.
Q. No. 1. Select the best option/answer and fill in the appropriate box on the Answer Sheet. (20)
(i) If A = 6i – 8j, then 4A has the magnitude:
(a) 40
(b) 10
(c) 20
(d) None of these
(ii) Let A = 2i + 6j – 3k and B = 4i + 2j + k, then A.B equals:
(a) 8i + 12j – 3k
(b) 17
(c) 23
(d) None of these
(iii) If ∇ is an operator, then ∇.V means:
(a) Gradient of a Scalar Field
(b) Curl of a Vector Field
(c) Divergence of a Vector Field
(d) None of these
(iv) The volume of a parallelepiped bounded by vectors A, B and C can be obtained from the expression:
(a) (A × B) . C
(b) (A . B) × C
(c) (A × B) × C
(d) None of these
(v) A force acting on a particle is conservative if:
(a) It obeys Newton’s Third Law
(b) It obeys Newton’s Second Law
(c) Its work equals the change in Kinetic Energy
(d) None of these
(vi) A torque applied to a rigid object always tends to produce:
(a) A rotational acceleration
(b) A linear acceleration
(c) Precession
(d) None of these
(vii) When the velocity of a body is constant, its acceleration is:
(a) Maximum
(b) Zero
(c) Infinity
(d) None of these
(viii) In the absence of external torque, the total angular momentum is:
(a) Constant
(b) Zero
(c) Infinity
(d) None of these
(ix) The rate of change of momentum of a particle is:
(a) Energy
(b) Force
(c) Impulse
(d) None of these
(x) Constructive and destructive superposition of waves is observed in:
(a) Polarization
(b) Interference
(c) Diffraction
(d) None of these
(xi) The intensity of a wave is proportional to the square of:
(a) Amplitude
(b) Time
(c) Intensity
(d) None of these
(xii) The colours in soap bubbles, oil slicks, etc. in a thin film are due to:
(a) Diffraction
(b) Polarization
(c) Interference
(d) None of these
(xiii) For higher resolution in a diffraction grating, one needs to have:
(a) Large number of rulings
(b) Small number of rulings
(c) No rulings at all
(d) None of these
(xiv) To produce interference, the sources must be:
(a) Intense
(b) Incoherent
(c) Coherent
(d) None of these
(xv) Interference fringes are of:
(a) Unequal width
(b) Equal width
(c) Variable width
(d) None of these
(xvi) A Carnot Cycle is:
(a) A rectangle on a P-V graph
(b) Bounded by two isotherms and two adiabatic curves
(c) Any four-sided process on a P-V graph
(d) None of these
(xvii) In an Adiabatic process:
(a) The temperature of the system remains constant
(b) The temperature of the system must change
(c) The internal energy of the system remains constant
(d) None of these
(xviii) A Carnot Cycle heat engine operates between 227°C and 127°C. Its efficiency is:
(a) 44%
(b) 20%
(c) 79%
(d) None of these
(xix) Metal pipes carrying water sometimes burst in winter because:
(a) Water expands
(b) Ice expands when it melts
(c) Metal contracts more than water
(d) None of these
(xx) A Fahrenheit thermometer and Celsius thermometer show the same reading at:
(a) 200°
(b) –40°
(c) 100°
(d) None of these
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). (05)
(c) For what value of ‘a’ are the vectors A = 2i + aj + k and B = 4i – 2j – 2k perpendicular? (04)
Q. No. 3.
(a) Distinguish between Linear and Angular Momentum. Explain the Law of Conservation of Angular Momentum. Prove that the Angular Momentum is constant in the absence of external torque. (14)
(b) The angular momentum J of a particle is given as:
J = 8t⁴i – 2t²j + 12t³k
Find the torque τ at t = 1. (06)
Q. No. 4.
(a) Discuss in detail the relativity of mass, time and length. (05)
(b) What is Time Dilation? Explain with example. (11)
(c) When we say that a clock in a moving frame runs slower than a clock in a stationary frame, what does it mean? (04)
Q. No. 5.
(a) Differentiate between Streamline and Turbulent Motion of a liquid. (03)
(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? (03)
Q. No. 6.
(a) What is Polarization of Light? Explain Polarization by Reflection and obtain Brewster’s Law. Also explain the idea of Double Refraction. (13)
(b) We wish to use a Quartz sheet (n = 1.54) in air as a polarizer. Find the polarizing angle and angle of refraction. (05)
(c) Why can’t we polarize sound waves? (02)
Q. No. 7.
(a) Define Internal Energy. State and explain the First and Third Laws of Thermodynamics. (14)
(b) What is a Heat Engine? Determine the efficiency of the engine if it takes 10,000 J of heat and delivers 2,000 J of work per cycle. (06)
Q. No. 8.
Write notes on ANY TWO of the following: (20)
(a) Centre of Mass
(b) Diffraction Grating and Resolving Power
(c) Production of Low Temperature
PAPER-II (Objective) 20 Marks
PART-I
Q. No. 1. Select the best option/answer and fill in the appropriate box on the Answer Sheet. (20)
(i) A Watt – sec is a unit of:
(a) Force
(b) Energy
(c) Power
(d) None of these
(ii) The direction of any magnetic induction effect is such as to oppose the cause of the effect. This is:
(a) Coulomb’s Law
(b) Ampere’s Law
(c) Lenz’s Law
(d) None of these
(iii) A magnetic field cannot:
(a) Accelerate a charge
(b) Exert a force on a charge
(c) Change the kinetic energy of a charge
(d) None of these
(iv) The inverse of resistivity is called Conductivity. Its unit is:
(a) Ohm⁻¹
(b) Ohm-metre
(c) (Ohm-metre)⁻¹
(d) None of these
(v) An LRC Circuit has R = 4 Ω, XC = 3 Ω and XL = 6 Ω. The impedance of the circuit is:
(a) 5 Ω
(b) 7 Ω
(c) 13 Ω
(d) None of these
(vi) A “step-down” transformer is used to:
(a) Increase the power
(b) Decrease the voltage
(c) Increase the voltage
(d) None of these
(vii) Electrical potential is the potential energy per unit:
(a) Charge
(b) Voltage
(c) Force
(d) None of these
(viii) The force on a charge moving with velocity v in a magnetic field B is given by:
(a) F = q/v × B
(b) F = q(v × B)
(c) F = qv + B
(d) None of these
(ix) A changing current “i” in any circuit induces an emf “e” in that circuit, which is equal to:
(a) e = di/dt
(b) e = i(dΦ/dt)
(c) e = −L(di/dt)
(d) None of these
(x) Inductive reactance of an inductor is:
(a) XL = ω²L
(b) XL = ω/L
(c) XL = ωL
(d) None of these
(xi) The resonant frequency of an LC circuit is:
(a) f = 2πLC
(b) f = 1/(2π√LC)
(c) f = 1/(2LC)
(d) None of these
(xii) The deliberate addition of an impurity element in a semiconductor is called:
(a) Doping
(b) Annealing
(c) Mixing
(d) None of these
(xiii) The conversion of AC into DC is called:
(a) Amplification
(b) Rectification
(c) Modulation
(d) None of these
(xiv) The laser light is:
(a) Monochromatic
(b) Coloured
(c) Chromatic
(d) None of these
(xv) The laser light may be obtained from:
(a) Quartz crystal
(b) NaCl crystal
(c) Ruby crystal
(d) None of these
(xvi) The emission of photoelectrons in photoelectric effect is dependent on:
(a) Threshold frequency
(b) Intensity of light
(c) Nature of metal
(d) None of these
(xvii) Which one of the following is NOT needed in a nuclear fission reactor?
(a) Fuel
(b) Accelerator
(c) Moderator
(d) None of these
(xviii) The half-life of a radioactive isotope is 140 days. How many days would it take to lose 3/4 of its initial activity?
(a) 105 days
(b) 280 days
(c) 35 days
(d) None of these
(xix) Most of the energy produced in the Sun is due to:
(a) Nuclear fusion
(b) Chemical reaction
(c) Nuclear fission
(d) None of these
(xx) A U-235 nucleus will split when it captures:
(a) An α-particle
(b) Electromagnetic radiation
(c) Neutron
(d) None of these
PAPER-II (Subjective) 80 Marks
PART-II
Attempt ONLY FOUR questions from PART-II, ALL Questions carry EQUAL marks.
Q.2.
(a) State and prove Gauss’s Law in electrostatics and express the law in differential form. (14)
(b) Find the electric intensity at a point outside a volume distribution of charge confined into a spherical region of radius R. (06)
Q.3.
(a) State and explain Ampere’s Law. Derive an expression for the value of B inside a solenoid. (14)
(b) A thin 10 cm long solenoid has a total of 400 turns of wire and carries a current of 0.20 A. Calculate the magnetic field inside near the centre.
Given: μ₀ = 12.57 × 10⁻⁷ T·m/A. (06)
Q.4.
(a) How is a semiconductor diode used as a half-wave and full-wave rectifier? (08)
(b) What are transistors? Give the construction and symbols of PNP and NPN transistors. (07)
(c) The resistivity of a metal increases with increase in temperature while that of a semiconductor decreases. Explain. (05)
Q.5.
(a) Discuss briefly the wave nature of matter and obtain an expression for de Broglie’s wavelength for matter waves. (14)
(b) Calculate the de Broglie wavelength of a 0.20 kg ball moving with a speed of 15 m/s. (06)
Q.6.
(a) Derive Einstein’s photoelectric equation on the basis of quantum theory. (14)
(b) Calculate the work function of sodium (Na) in electron-volts, given that the threshold wavelength is 6800 Å and h = 6.625 × 10⁻³⁴ J·s. (06)
Q.7.
(a) Define the terms decay constant, half-life and average life as applied to a radioactive substance. Find the relation between them. (11)
(b) The half-life of Radium is 1590 years. In how many years will one gram of pure element:
(i) Lose one centigram?
(ii) Be reduced to one centigram? (07)
(c) When a nucleus emits a γ-ray photon, what happens to its atomic number and its actual mass? (02)
Q.8.
Write notes on ANY TWO of the following: (20)
(a) Self and Mutual Inductance
(b) Pauli’s Exclusion Principle
(c) Compton Scattering
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