SET-2 free surface current density at the
Central University of Jharkhand CUJ/ PHY/621010/2021 interface, C) contribution of volume
Department of Physics charge density, D) none of these.
2nd Semester (2 Years M. Sc. in Physics) Examination-2021 3. Which statement is most correct? 2
Paper Name: Classical Electrodynamics
(Code: PHY/621010) A) the electromagnetic fields not only
Full Marks: 60 Time: 2 Hrs. carry energy, but also carry momentum,
B) the radiation pressure is proportional to
INSTRUCTIONS:
intensity of incident electromagnetic wave,
1. Question paper is divided into two Sections A and B. Attempt the
required number of questions as per the instruction mentioned in C) the energy flux density transported by
each Section. the fields is along the direction of
2. Numbers showing in right side indicating marks.
propagation and which is energy density
Section: A (Answer all questions) (Total 20 marks) times the velocity of waves,
S. No Question Marks D) All the above.
4. When the electromagnetic waves 2
1. Maxwell`s equations provide A) existence 2 propagate through a linear homogeneous
of magnetic charge would explain why media at a speed v, the refractive index of
electric charge is quantized, B) there is
the media n r , where r is dielectric
symmetry between the electric and
magnetic field, C) how charges produce constant of the media. As r for water is
the fields; reciprocally the force law tells 80, so, n 9. But, from the measured
how fields affect the charges, D) all of value is 1.33. Therefore, the fact may be
these. understood as
2. The parallel components of magnetic field 2 A) because of phenomena of dispersion,
intensity are discontinuous because of A)
contribution of volume current density, B) B) the refractive index is 9 for the
1
experiment is done in the radio frequency media),
region,
D) sin B n (refractive index of the
C) the refractive index is 1.33 for the
experiment is carried out in the optical media).
frequency region,
7. Which one is correct? 2
D) All of the above.
A) to get retarded potentials, the time
5. The Rayleigh scattering cross section 2 dependent generalization of electric and
depends upon the frequency of incident magnetic potentials one must replace
photon as A) 2 , B) 4 , C) , D) none current time by retarded time in the
of the above. magnetostatic and electrostatic formulas,
6. The Brewster`s angle informs that 2 B) the Coulomb Gauge is very simple to
calculate the vector potential, whereas it is
A) the intermediate angle between the very difficult to calculate scalar potential,
normal incidence and grazing angle of
C) the Gauge transformation provides
incidence, at which the reflected wave is there is no effect on electric and magnetic
completely extinguished, field in such a way the new scalar potential
comes after addition of time variation
B) the intermediate angle between the scalar function with old scalar potential
and new vector potential comes after
normal incidence and grazing angle of
addition of space variation scalar function
incidence, at which the transmitted wave is with old vector potential,
completely extinguished,
D) None of these.
C) tan B n (refractive index of the
2
8. The electric dipole radiation provides that 2 10. The Newton`s 3rd law in electrodynamics 2
informs that A) there is a violation of
A) there is no radiation along the axis of Newton`s 3rd law, B) electric force obeys
the dipole, the Newton`s 3rd law, but magnetic force
B) the intensity profile takes the form of does not, C) whatever momentum is lost to
donut; with its maximum in the equatorial the particles is gained by the particles,
plane, thus, field momentum is added to
mechanical momentum of the charges and
C) the total radiated power is constant and hence, total momentum is conserved, D)
is varying with w4 ( w is the frequency of None of these.
monochromatic waves travelling along
radial direction).
D) All of above. Section: B (Answer any eight questions) (Total 40 marks)
9. Choose the correct one. 2 S. No Question Marks
A) For a moving point charge, vector
11. What is the utility of retarded potential? 5
potential is not related scalar potential of
How can you confirm your consideration
it,
for retarded potentials of non-static
B) The magnetic field of a point charge is sources is right? -justify your answer.
always perpendicular to the electric field 12. Find out time-dependent configurations of 5
and to the vector from the retarded point, scalar and vector potentials using
Maxwell’s equations.
C)The radiated power may be calculated
from the time independent fields, 13. Find out the expression of intensity when 5
monochromatic plane wave propagates in
D) For magnetic dipole radiation, the a linear media.
scalar potential is not zero.
3
14. Show that total energy is conserved for 5
reflection and transmission at normal
incidence of the boundary between two
linear media.
15. A) Find out the differential form of 5
conservation of momentum. What is the
meaning of it? B) Find out the wave
equation of an electromagnetic wave in
vacuum.
16. Find out the expression of momentum 5
density and intensity transported by
electromagnetic wave.
17. Find out the expression of Fresnel’s 5
equations, for the case of polarization in
the plane of incidence. What is Brewster’s
angle?
18. Prove that excellent conductors make 5
good mirrors.
19. Why cannot TEM waves occur in a 5
hollow wave guide? How does coaxial
transmission line support the TEM
waves?
20. Prove that electromagnetic wave is 5
transverse in nature.
