IISER Physics - Electromagnetic Waves
Exam Duration: 45 Mins Total Questions : 30
What is the progation velocity of an electromagnetic wave in a medium for which relative permittivity, \({ \epsilon }_{ r }\) = 3.1, and relative permeability, \({ \mu }_{ r }\) = 200 ?
- (a)
3.0 \(\times\) 1010 ms-1
- (b)
1.20 \(\times\) 107 ms-1
- (c)
3.60 \(\times\) 107 ms-1
- (d)
1.5 \(\times\) 108 ms-1
A viberating electric charge radiates
- (a)
electric waves
- (b)
magnetic waves
- (c)
both (a) and (b)
- (d)
light waves
In an electromagnetic wave, light vector is
- (a)
electric vector
- (b)
magnetic vector
- (c)
electromagnetic vector
Displacement current
- (a)
is same as conduction due to flow of electrons
- (b)
is same as conduction due to flow of positive ions
- (c)
is same as conduction due to flow of negative ions and positive ions
- (d)
is not same as conduction due to flow of time varying electric field.
The law which states that time varying electric field produces magnetic field is
- (a)
Gauss law of magnetism
- (b)
Biot savart law
- (c)
Faraday's law of electromagnetic induction
- (d)
Ampere's law in its modified form
T.V. signals cannot be transmitted
- (a)
by ground wave propagation because they are absorbed by the atmosphere
- (b)
by ground wave propagation because they have low frequency
- (c)
by sky wave propagation because they penetrate ionosphere and die in the upper part of atmosphere
- (d)
by sky wave propagation because they have low frequency
If \({ \mu }_{ 0 }\) and \({ \epsilon }_{ 0 }\) represent the permeability and permittivity of vacuum and \(\mu\) and \(\epsilon\) represent the permeability and permittivity of the medium, then the refractive index of the medium is :
- (a)
\(\sqrt { \frac { { \mu }_{ 0 }{ \epsilon }_{ 0 } }{ { \mu \epsilon } } } \)
- (b)
\(\sqrt { \frac { \mu }{ { \mu }_{ 0 }{ \epsilon }_{ 0 } } } \)
- (c)
\(\sqrt { \frac { { \epsilon } }{ { \mu }_{ 0 }{ \epsilon }_{ 0 } } } \)
- (d)
\(\sqrt { \frac { \mu \epsilon }{ { \mu }_{ 0 }{ \epsilon }_{ 0 } } } \)
The relation between refractive index n and dielectric constant \(\epsilon_r\) of a medium is
- (a)
\(n\equiv { \epsilon }_{ r }\)
- (b)
\(n\equiv \sqrt { { \epsilon }_{ r } } \)
- (c)
\(\sqrt { n } \equiv { \epsilon }_{ r }\)
- (d)
\(n\equiv { \left( { \epsilon }_{ r } \right) }^{ -1/2 }\)
An electronic wave is propagating along z-axis. Which of the following pairs of space and time varying fields would generate such a wave?
- (a)
Ex, By
- (b)
Ez, Bx
- (c)
Ez, Bx
- (d)
Ey, Bz
Electromagnetic theory was established because of the discovery of
A. Concept of displacement currrent
B. Gauss's law of electrostatics and that of magnetism
C. A,pere's law of electricity
D. Faraday's law of electromegnatic induction
Mark
- (a)
If A is correct only
- (b)
If B, C are correct only
- (c)
If C, D are correct only
- (d)
if B, C, D are correct only
Expression \({ \epsilon }_{ 0 }\oint { \overset { \rightarrow }{ E } .d\overset { \rightarrow }{ s } } \) represents
- (a)
charge
- (b)
current
- (c)
electric flux
- (d)
electified
Microwaves are better carriers of signals for long range transmission then radiowaves because
- (a)
microwaves have much shorter wavelength
- (b)
microwaves travel at a faster speed
- (c)
microwaves suffer minimum dispersion
- (d)
microwaves suffer minimum deviation
Which of the following laws asserts that the electric field lines cannot form closed loops
- (a)
Gauss's law
- (b)
Faraday's law
- (c)
Unmodified Ampere's law
- (d)
Modified Ampere's law
The structure of solids is investigated by using
- (a)
cosmic rays
- (b)
x-rays
- (c)
\(\gamma\)-ray
- (d)
infra-red radiation
Electromagnetic waves travel only through
- (a)
material medium such as air, water
- (b)
electric or magnetic fields
- (c)
electric and magnetic fields whose directions are perpendicular
- (d)
in space wher ther is no electric or magnatic fields
The energy of visible light is of the order of
- (a)
a few eV
- (b)
a few MeV
- (c)
a few keV
- (d)
\(\frac{1}{1000}\)eV
According to Maxwell's hypothesis, a changeing electric field vector gives rise to
- (a)
an electric current
- (b)
a magnetic field
- (c)
an induced e.m.f
- (d)
radiation pressure
The frequency of x-rays, \(\gamma\)-rays and ultraviolet rays are respectively a, b and c. Then
- (a)
a < b, b > c
- (b)
a > b, b > c
- (c)
a > b, b < c
- (d)
a < b, b < c
A certain e.m. wave has a maximum electric field vector of 0.5 Vm-1. What is the maximum magnetic field vector?
- (a)
1.67 \(\times\) 10-9 N/Am
- (b)
1.67 \(\times\) 10-8 N/Am
- (c)
1.67 \(\times\) 109 N/Am
- (d)
NONE OF THESE
A certain e.m. wave the electric field was found to oscillate with an amplitude of 0.5 Vm-1. The intensity of the wave is
- (a)
3.314 \(\times\) 10-4 Wm-2
- (b)
3.14 \(\times\) 10-4 Wm-2
- (c)
33.14 \(\times\) 10-14 Wm-2
- (d)
331.4 \(\times\) 10-4 Wm-2
An L-C oscillator has a capacitor of 400 pF and an inductor of 100 \(\mu H\). It is used in an antenna radiating electromagnetic wave of wavelength
- (a)
375 m
- (b)
257 m
- (c)
189 m
- (d)
405 m
The dimension of \({ \varepsilon }_{ 0 }\frac { d{ \phi }_{ E } }{ dt } \) is same as the dimension of
- (a)
charge
- (b)
capacitance
- (c)
potential
- (d)
current
A parallel plate capacitor has plate area 0.32 m2 and the distance between its plates is 5 mm. The voltage between the plates of the capacitor is raised to 1200 V. The average value of displacement current, when it is charged for one microsecond, is
- (a)
3.80 A
- (b)
6.80 A
- (c)
0.38 A
- (d)
0.68 A
A plane of electromagnetic wave travel in free space along X-axis. At a particular point in space, the electric field along Y-axis is 9.3 V/m. The magnetic induction is
- (a)
3.1 x 10-8 T
- (b)
3 x 10-5 T
- (c)
3 x 10-6 T
- (d)
9.3 x 10-6 T
The energy stored in 40 cm length of laser beam operated at 3 mW, is
- (a)
6 x 10-12 J
- (b)
9 x 10-12 J
- (c)
6 x 10-10 J
- (d)
9 x 10-15 J
The wavelength of X-rays lies between
- (a)
maximum to infinite limits
- (b)
minimum to certain limits
- (c)
minimum to infinite limits
- (d)
infinite to infinite limits
The wavelength of infrared rays is of the order of
- (a)
5 x 10-7 m
- (b)
10-3 m
- (c)
10-7 to 10-3 m
- (d)
1011 to 109 m
During the propagation of electromagnetic waves in a medium
- (a)
Electric energy density is equal to the magnetic energy density
- (b)
Both electric and magnetic energy densities are zero
- (c)
Electric energy density is double of the magnetic energy density
- (d)
Electric energy density is half of the magnetic energy density
Match List-I (electromagnetic wave type) with List-II (its association/application) and select the correct option from the choices given below the lists
List-I | List-II |
A. Infrared waves | (i) To treat muscular strain |
B. Radio waves | (ii) For broadcasting |
C. X-rays | (iii) To detect fracture of bones |
D. Ultraviolet rays | (iv) Absorbed by the ozone layer of the atmosphere |
- (a)
A B C D (iii) (ii) (i) (iv) - (b)
A B C D (i) (ii) (iii) (iv) - (c)
A B C D (iv) (iii) (ii) (i) - (d)
A B C D (i) (ii) (iv) (iii)
Electromagnetic waves are transverse in nature is evident by
- (a)
polarisation
- (b)
interference
- (c)
reflection
- (d)
diffraction