UPSC Physics 2026

(a) A uniform rod of length L and mass m stands vertically upright on a rough floor and then tips over. What is the rod's angular velocity when it hits the floor? (10 marks) (b) A…

(a) What is meant by achromatic combination of lenses? Derive the condition for achromatization of a pair of lenses separated by a distance x. The two lenses have different disper…

(a) The energy of a photon is expressed as E = hν, where h is the Planck's constant and ν is the frequency of the photon. The momentum of the photon is hν/c, where c is the speed…

(a) (i) In Newton's ring experiment, the space between planoconvex lens and glass plate is filled with a liquid of refractive index μ. Explain how interference pattern changes as…

(a) Calculate the effective resistance of the following combination of resistances as shown in the figure and determine the voltage drop across each resistance when a potential di…

(a) Discuss the origin of hysteresis in ferromagnetic materials on the basis of domain theory. Explain how domain wall motion and pinning lead to energy loss during cyclic magneti…

(a) A gas has only two particles a and b. Show with the help of diagrams how these two particles can be arranged in three energy states 1, 2, 3 using (i) Maxwell-Boltzmann, (ii) F…

(a) The space between the plates of a parallel-plate capacitor is filled with a dielectric material whose susceptibility varies linearly from 0 at the bottom plate (x = 0) to 1 at…

(a) (i) The de Broglie wavelength of a particle in thermal equilibrium at a temperature of 27°C is λ. At what temperature will it be λ/2 ? (ii) The wave function of a spin 1/2 par…

(a) A particle is in the ground state of a 1-D simple harmonic oscillator potential, V(x) = 1/2 mω²x². Calculate the position uncertainty of the particle. (15 marks) (b) (i) A par…

(a) (i) Calculate the number of permitted electrons in a sub-shell and a shell in an atom. (ii) Explain how Pauli's exclusion principle helps in determining the electronic configu…

(a) (i) What are hot bands in vibrational spectroscopy ? Why are they called so ? (8 marks) (ii) The fundamental and 2nd harmonic transitions of ¹⁴N¹⁶O are recorded at 1876·06 cm⁻…

(a) Are the nucleons inside the nucleus governed by the laws of quantum physics ? Justify your answer. (10 marks) (b) Binding energy and rest mass energy of a two-nucleon bound st…

(a) By considering the three-dimensional harmonic oscillator potential, explain the energy levels of nucleons inside the nucleus. Also, derive the zero-point energy of nucleons. W…

(a) (i) What is diamagnetism ? Why do diamagnetic materials have negative magnetic susceptibility ? (ii) Discuss the limitations of the quantum theory of diamagnetism. (iii) Draw…

(a) (i) Discuss the Debye model of lattice specific heat. What are the limitations of the Debye model ? (10 marks) (ii) At very low temperatures, the specific heat of rock salt va…