CSS past paper

CSS Physics Paper I Past Paper 2026

CSS Physics Paper I 2026 carries 100 marks over 3 hours. It has 7 questions.

Marks: 100
Time: 3 hours
Questions: 7

Years

How to attempt: Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.

Questions

Question 1 (Part I) is the paper's MCQs, which are not reproduced here.

Q. 2
(20)
- (a)
  What is the difference between Divergence, Gradient, and Curl. Give one example of each.
  (10)
- (b)
  A particle moves in the $xy$ plane, starting from the origin at $t$ = 0 with an initial velocity having an $x$ component of 20 m/s and a $y$ component of -15 m/s. The particle experiences an acceleration in the $x$ direction, given by $a_{x}$ = 4 m/s $^{2}$ . Determine the total velocity vector at any time.
  (10)
Q. 3
(20)
- (a)
  What is law of conservation of angular momentum? Give at least one example.
  (8)
- (b)
  A 6 kg block initially at rest is pulled to the right along a horizontal surface by a constant horizontal force of 12N. Find the speed of the block after it has moved 3m if the surfaces in contact have a coefficient of kinetic friction of 0.15.
  (10)
- (c)
  Can a normal force do work? If not, why not? If so, give an example.
  (2)
Q. 4
(20)
- (a)
  What is Kepler’s third law? Prove that the square of the period is proportional to the cube of the semimajor axis.
  (12)
- (b)
  Consider a satellite of mass $m$ moving in a circular orbit around the Earth at a constant speed $v$ and at an altitude $h$ above the Earth’s surface. Determine the speed of satellite in terms of $G$ (Universal Gravitational Constant), $h$ , $R$ (the radius of the Earth), and $M$ (the mass of the Earth).
  (8)
Q. 5
(20)
- (a)
  What is Bernoulli’s Theorem? Show that
  (10)
  $P + \frac{1}{2}\rho \mathrm{v}^{2} + \rho gh = constant$
  Where P is pressure of the fluid, ρ is density of the fluid, v is velocity of the fluid, g is acceleration due to gravity, and $h$ is height above a reference level.
- (b)
  In a car lift used in a service station, compressed air exerts a force on a small piston that has a circular cross section of radius 5 cm. This pressure is transmitted by a liquid to a piston that has a radius of 15 cm. What force must the compressed air exert to lift a car weighing 1000 N?
  (10)
Q. 6
(20)
- (a)
  What is Young’s double-slit experiment? Derive the mathematical formula for constructive and destructive interference of light.
  (12)
- (b)
  A 200g block connected to a light spring for which the force constant is 5 N/m is free to oscillate on a frictionless, horizontal surface. The block is displaced 5cm from equilibrium and released from rest. Find the period of its motion.
  (8)
Q. 7
(20)
- (a)
  What is diffraction of light? Explain diffraction of X-rays by crystals.
  (10)
- (b)
  Monochromatic light from a helium–neon laser ( $\lambda = 632$ nm) is incident normally on a diffraction grating containing 4000 grooves per centimeter. Find the angles at which the second-order maximum is observed.
  (10)
Q. 8
(20)
- (a)
  What is first-law of thermodynamics? Show that work done on the gas during isothermal expansion of an ideal gas is $W = nRT\,\ln\left(\frac{V_{i}}{V_{f}}\right)$ , where $R$ is universal gas constant, $T$ is temperature, $n$ is number of moles. $V_{i}$ and $V_{f}$ is the initial and final volume, respectively.
  (12)
- (b)
  A 1 mole sample of an ideal gas is kept at 0°C during an expansion from 3 L to 10 L. How much work is done on the gas during the expansion?
  (8)

Part-II is to be attempted on the separate Answer Book.
Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.
All the parts (if any) of each Question must be attempted at one place instead of at different places.
Write Q. No. in the Answer Book in accordance with Q. No. in the Q.Paper.
No Page/Space be left blank between the answers. All the blank pages of Answer Book must be crossed.
Extra attempt of any question or any part of the question will not be considered.
Use of Calculator is allowed.