BPHET-141 · December 2025 · English
IGNOU BPHET-141 December 2025 Previous Year Question Paper
ELEMENTS OF MODERN PHYSICS
Structured previous year question paper for BPHET-141, December 2025 session.
Max marks: 50 · Questions: 5
Verified: 24 Aug 2026
BACHELOR OF SCIENCE (GENERAL)
(B. SC. G)
Term-End Examination
December, 2025
BPHET-141 : ELEMENTS OF
MODERN PHYSICS
Time : 2 Hours Maximum Marks : 50
Note:
(i) Attempt all questions.
(ii) The marks for each question are
indicated against it.
(iii) Symbols have their usual meanings.
(iv) You may use a calculator.
(v) The values of physical constants are
given at the end.
Q1.Answer any five parts : 5x2=10
(a) Distinguish between Galilean and Einsteinian principles of relativity.
(b) The mean life time of a free neutron at rest is measured to be 900 s. What is its mean life time measured by an observer with respect to whom the neutron travels at a speed of 0.9 c?
(c) Calculate the de Broglie’s wavelength of a 1.0 MeV electron.
(d) What is the probabilistic interpretation of the wave function ?
(e) Define and draw a step potential of step Vo>Oat x=0.
(f) Explain briefly how quantum tunneling enables alpha decay from the atomic nucleus.
(g) What is secular equilibrium in radioactivity ?
(h) Write the functions of slim rods and safety rods in a nuclear reactor.
Q2.Answer any two parts: 2x5=10
(a) Show that simultaneous events that occur in an inertial frame of reference S at different positions are not simultaneous in another inertial frame of reference S' moving uniformly with respect to S. 5
(b) A spaceship is receding from the Earth at a speed of 0.25 c. An observer in the spaceship measures the wavelength of light from a source in it as 500 nm. What is the wavelength of this light as measured by an observer on _ the Earth ? 5
(c) The rest energy of a _ particle is 1000 MeV. Calculate its linear momentum and total energy (in MeV) given that it travels at a speed of 0.6 c.
Q3.Answer any two parts : 2x5=10
(a) The wave function of a particle of mass m and zero energy is given by : w(x) = Nee, where N is a constant. Write down the time-independent Schrédinger equation for the particle and determine its potential energy.
(b) Use the uncertainty principle to explain the concept of zero-point energy.
(c) Calculate (x) for the wave function vie) = |Peos(%), O<x<L
Q4.Answer any one part: 1x10=10
(a) Write down the time-independent Schrédinger equation for a particle of mass m in a one-dimensional potential barrier of height Vy and width a. Obtain the general solutions of the equation when the energy of the particle E > Vo. Write down the boundary conditions for the problem.
(b) Show that for a symmetric potential function [V(x) = V(-x)], the parity operator commutes with the Hamiltonian.
Q5.Answer any two parts: 2x5=10
(a) Define ‘activity’ of a radioactive substance. The half life of an element is