CSS past paper

CSS Physics Paper II Past Paper 2026

CSS Physics Paper II 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)
  State and explain Gauss’ law in dielectrics. Also give its significance.
  (5)
- (b)
  Derive a mathematical expression for an electric field at a point lying outside of a uniformly charged spherical shell.
  (5)
- (c)
  A spherical shell has a total charge $q = 4\mu C$ and radius $0.3\ m$ . Calculate the electric field at a distance of $.5\ m$ from the center of the shell.
  (10)
Q. 3
(20)
- (a)
  What is meant by induced emf? Why is it called induced?
  (10)
- (b)
  Derive an expression for induced emf in a coil with N turns due to changing magnetic flux.
  (5)
- (c)
  Magnetic flux through a 20 turn coil changes from 0.5 to 0.1 Wb in 0.2 s. How much emf would be induced in the coil?
  (5)
Q. 4
(20)
- (a)
  Discuss the time-independent Schrodinger wave equation. Why is it called time independent?
  (5)
- (b)
  Solve the time-independent Schrodinger wave equation for a particle in a one-dimensional potential well of width of L.
  (5)
- (c)
  Find the ground-state energy of electron in a 1-D potential well with L = 1 nm. Mass of electron = m = 9.11 × 10 $^{-31}$ kg.
  (10)
Q. 5
(20)
- (a)
  What is meant by Bravais lattice?
  (5)
- (b)
  Calculate the volume of the base-centered cubic structure of side length 0.4 $nm$ . The volume needs to be in Å $^{3}$ .
  (5)
- (c)
  Clearly elaborate the difference between base-centered and face-centered cubic lattices. Also discuss types of base-centered cubic cell.
  (10)
Q. 6
(20)
- (a)
  Define Fermi sphere. Is this an energy state? Explain.
  (10)
- (b)
  Deduce the Fermi-Dirac distribution function
  (5)
  $f(E,T) = \frac{1}{e^{(E-E_{F})/K_{B}T} + 1}$
  for Fermi energy level ( $E = E_{F}$ )
- (c)
  Calculate the Fermi energy for Cu in $eV$ with number density ( $n$ ) of $8.49 \times 10^{28}\, {}^{atoms}\!/_{m^{3}}$
  (5)
  $\left[E_{F} = \frac{h^{2}}{2m}\left(\frac{3n}{8\pi}\right)^{2/3}, m = 9.11 \times 10^{-31}Kg, h = 6.62 \times 10^{-34}J.s\right]$
Q. 7
(20)
- (a)
  Explain on scientific grounds the difference between alpha, beta and gamma decay.
  (5)
- (b)
  Write the decay equation for the alpha decay of $U_{92}^{238}$ .
  (5)
- (c)
  The charge number and mass number of two nuclei $A$ & $B$ are the same. But their binding energies are such that $(B.E)_{A} > (B.E)_{B}$ . Which nucleus will have more mass and why?
  (10)
Q. 8
(20)
- (a)
  Explain nuclear fission with the help of one practical application.
  (5)
- (b)
  What are elementary and composite particles? Give two examples from each family of elementary particles.
  (5)
- (c)
  What is controlled fusion? Why is it hard to achieve on earth?
  (10)

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.