M. Sc. Physics (Materials Science) (Semester II)
(CBCS) Examination, 2017
ELECTRODYNAMICS
Day Date: Friday, 21-04-2017 Max. Marks: 70
Time: 10.30 AM to 01.00 PM
N.B. Q.1 and Q.2 is compulsory.
Attempt any three questions from Q. 3 to 7.
Figures to the right indicate full marks.
Q.1 Choose correct alternatives: 08
When a potential difference is applied across human heart, its
behavior can be modeled as that of electric dipole. Abnormal
hearts can be detected by mapping.
Equipotential surfaces Electric flux lines
Electric fields All of the above
The electric flux density D is
normal tangential
opposite unrelated
to the electric flux lines
The electric field E is
normal b tangential opposite d unrelated
If a dipole is displaced through a small distance and the
original dipole is then replaced by one of the same magnitude
but of opposite sign
a monopole is formed multipoles are formed
octupole is formed quadrupole is formed
The depth of penetration is defined as that depth in which the
wave attenuates to
.50% of its strength before penetration
20% of its strength before penetration
70% of its strength before penetration
I/e times of its strength before penetration
The formulae relating the amplitude of the reflected and
transmitted waves with that of incident wave are known as
.Fresnel formulae .Fraunhofer formulae
.Kirchhoff formulae .Maxwell formulae
An electromagnetic wave has electric field component along ydirection
and magnetic field cpmmponent along x-direction.
The electromagnetic wave is propagating along
Page 2 of 2
.z direction b . direction c . x direction y direction
In a good conductor, for electromagnetic wave operating at 1
GHz, the E and H will be out of phase at a distance
by
45o 30o 60o 90o
True or False: 06
Even if Poynting vector is zero, some electromagnetic energy
can flow across a closed surface-
Maxwell's equations are viewed as a unification of magnetic
and electric forces.
The field vectors E and H are attenuate exponentially as the
wave penetrates the conducting medium.
Theory of steady current is called a Magnetostatics.
In electrostatics and magnetostatics, Newton's third law holds,
but in electrodynamics it does not.
The distance it takes to reduce the amplitude of
electromagnetic wave by a factor of I/e is called as skin depth.
Q.2 Write short answers on the following:
Write the boundary conditions for a linear media in terms of E and
B alone.
04
Write the Maxwell's equation for free space in differential form. 04
Write Maxwell's equation for a moving media. 04
Write the word statements of the Maxwell's equation written in
integral form.
02
Q.3 By considering the reflection and refraction of electromagnetic
waves at oblique incidence, derive three fundamental laws of
geometrical optics.
08
Obtain Poynting theorem for the conservation of energy for the
electromagnetic field.
06
Q.4 Write a note on Coulomb and Lorentz guage. 08
Obtain Wave equations in terms of electromagnetic potentials. 06
Q.5 Using the theory of electric dipole radiation explain the blueness
of the sky and redness of the sunset.
08
Find out the power radiated by an oscillating electric dipole and
describe its angular distribution.
06
Q.6 Find the directivity (maximum) of a half wave dipole. 08
Write a note on Gauge transformations. 06
Q.7 A plane electromagnetic wave is incident on a plane boundary
between the two non-conducting media. Specify the boundary
conditions and hence derive Fresnel's formulae for the reflected
and transmitted intensities.
08
Describe the use of Hertz potential in computation of radiation
fields.