The Indian Forest Service Examination is One of the Civil Service Examination that is Conducted by UPSC Every year

the Questions paper of the IFS Physics Examination is as follow


Discuss that the motion of a particle in a central field gets restricted to a plane
provided its angular momentum is nonzero. What will happen if the angular
momentum is zero?

Find the velocity and momentum of a particle having rest mass m0
and kinetic energy equal to two times of its rest mass energy.

In Young's double-slit experiment, a thin mica sheet (refractive index= 1• 5) is
introduced in the path of one of the beams. If the central fringe gets shifted by
0•2 em, calculate the thickness of the mica sheet.
Assume separation between
the two slits (d) and between slit and source (D) as d = 0 • 1 em and D = 50 em.

Explain physically why dispersion is diminished in multimode parabolic-index
fiber than in step-index fiber .

Obtain the equation of motion of a simple pendulum using Lagrangian
formalism. Hence, obtain expression for the angular frequency of a simple
harmonic oscillator.

With a planoconvex lens of radius of curvature R resting on a plane glass
surface, Newton's rings are observed with incident light of wavelength A. Find
the radii of mth order dark rings. What will be the colour of the innermost ring
with white light illumination?

Deduce an expression for resolving power of a diffraction grating, explaining its
meaning. What will be the value of the number of slits in the grating to resolve
D1 and D2 lines of sodium in the first order, assuming A and t.A respectively as
600 nm and 0•6 nm?


Using Ampere's law, derive the magnetic field of a toroid (N turns each carrying
current I) of inner radius a and outer radius bat a distance r midway between
a and b.

Question paper of the IFS Physics Paper