JEE Main Physics - Electromagnetic Waves
Exam Duration: 60 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
For electomagnetic waves propagating along x-axis, the wave must have the components
- (a)
(Ex, Hy)
- (b)
(Ey, Ez)
- (c)
(Ey, Hy)
- (d)
(Hy, Ez)
Choose CORRECT statement :
- (a)
Hertz discovered eectromagnetic waves
- (b)
Maxwell discovered eectromagnetic waves
- (c)
Electromagnetic wave equations are four Maxwell's equations. They are called Maxwell's equations because they were discovered by Maxwell
- (d)
Marconi for the first time discovered eectromagnetic waves
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
A capacitor consists of two circular plates each of radius 12 cm and distance of separations is 5.0 mm. A constant current of 0.15 A charges the plates. Due to theis charging, the potential difference of 1.87 \(\times\) 109 V is developed in one second. The displacement current across the plates will be
- (a)
0.15 A
- (b)
0.015 A
- (c)
0.0015 A
- (d)
NONE OF THESE
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
Which of the following e.m. radiations has the smallest wavelength?
- (a)
U-V waves
- (b)
microwaves
- (c)
x-rays
- (d)
\(\gamma\)-ray
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
Which one of the following electromagnetic radiation has the smallest wavelength?
- (a)
ultraviolex waves
- (b)
x-rays
- (c)
\(\gamma\)-rays
- (d)
microwave
Radiowaves differact around builing although light waves do not. The reason is that radio waves
- (a)
travel with speed larger than c
- (b)
have much larger wavelength than light
- (c)
carry news
- (d)
are not electromagnetic waves
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
An electromagnetic wave crossing through vacuum is given by \(E={ E }_{ 0 }\sin { \left( kX-\omega t \right) } \) . The quantity independent from the wavelength of radiation is
- (a)
\(k\omega \)
- (b)
\(\frac { k }{ \omega } \)
- (c)
\({ \omega } \)
- (d)
k
The poynting vector for an electromagnetic wave is given by \(S=\hat { i } +\hat { j } +\hat { 2k } \). The value of cosine of the angle of direction of propagation with Y-axis would be
- (a)
\(\frac { 1 }{ \sqrt { 6 } } \)
- (b)
\(\frac{1}{6}\)
- (c)
\(\frac{1}{0.6}\)
- (d)
\(\frac{1}{2}\)
The charge on the plate of a parallel plate capacitor is given by \(q={ q }_{ 0 }\sin { \omega t } \). The separation between the two large plates of the capacitor having area A is d. The displacement current through the capacitor would be
- (a)
\(\frac { \omega }{ { \varepsilon }_{ 0 } } { q }_{ 0 }\cos { \omega t } \)
- (b)
\({ q }_{ 0 }\omega \cos { \omega t }\)
- (c)
\(\frac { d }{ A{ \omega }_{ 0 } } \)
- (d)
\(\frac { { \omega }^{ 2 } }{ { \varepsilon }_{ 0 } } { q }_{ 0 }\cos { \omega t } \)
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 intensity of an electromagnetic wave is 1.5 x 10-3 Wm-2. The wave falls on a surface and is completely absorbed by it. The pressure exerted by the wave on the surface is
- (a)
5 x 1012 Nm-2
- (b)
5 x 10-12 Nm-2
- (c)
6 x 10-12 Nm-2
- (d)
6 x 1012 Nm-2
Energy associated with electromagnetic wave is due to
- (a)
its wavelength
- (b)
its electric and magnetic vibrations
- (c)
its frequency
- (d)
its speed
In a parallel beam of light of intensity 2.0 Wm-2 , the amplitude of electric vibrations would be approximately
- (a)
40 NC-1
- (b)
20 NC-1
- (c)
50 NC-1
- (d)
60 NC-1
The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance would be
- (a)
\(\frac{E}{2}\)
- (b)
2E
- (c)
\(E\sqrt{2}\)
- (d)
\(\sqrt{2}E\)
A satellite is arbitrary around the earth. Solar energy is collected by a panel of area 5m2 . If solar radiations fall normally on the surface and completely absorbed by it. The value of average force imparted, will be (solar constant = 1.4 kWm-2)
- (a)
2.33 x 10-4 N
- (b)
2.33 N
- (c)
1.33 x 10-5 N
- (d)
2.33 x 10-5 N
The correct sequence of the increasing wavelength of the given radiation sources is
- (a)
radioactive sources, X-ray tube, crystal oscillator, sodium vapour lamp
- (b)
radio active source, X-ray tube, sodium vapour lamp, crystal oscillator
- (c)
X-ray tube, radioactive source, crystal oscillator, sodium vapour lamp
- (d)
X-ray tube, crystal oscillator, radioactive source, sodium vapour lamp
For an electromagnetic wave moving along X-axis \({ E }_{ y }=600\sin { \omega } \left( t-X/c \right) \). An electron is set to be in motion along Y-direction with a speed of 3 x 106 m/s. The sum of maximum electric force and magnetic force on the electron is (all the units are SI)
- (a)
\(\left( 9.6\times { 10 }^{ -17 }+9.6\times { 10 }^{ -19 } \right) N\)
- (b)
\(\left( 9.6\times { 10 }^{ -17 }+9.6\times { 10 }^{ -18 } \right) N\)
- (c)
\(\left( 9.6\times { 10 }^{ -19 }+9.6\times { 10 }^{ 21 } \right) N\)
- (d)
\(\left( 9.9\times { 10 }^{ -17 }+5.4\times { 10 }^{ -19 } \right) N\)
The plane electromagnetic wave having intensity 6 Wm-2 falls on mirror having area 20 cm2. The wave falls on the mirror normally. The momentum (in SI unit) imparted per second would be
- (a)
8 x 1011
- (b)
9 x 10-12
- (c)
10 x 10-12
- (d)
None of these
A source has radiating power P uniformly in all the directions. The strength of the electrical vibration at a distance d from the source is
- (a)
\(\sqrt { \frac { P }{ 2\pi { \varepsilon }_{ 0 }{ d }^{ 2 }c } } \)
- (b)
\(\sqrt { \frac { P }{ 2\pi { \varepsilon }_{ 0 }{ d }c } } \)
- (c)
\(\sqrt { \frac { P }{ \pi { \varepsilon }_{ 0 }{ d } c } } \)
- (d)
\(\sqrt { \frac { \pi }{ { \pi }^{ 2 }{ \varepsilon }_{ 0 }^{ 2 }{ d }c } } \)
Light with flux 18 W cm2. is normally incident on a non-reflecting surface having area 20 cm2. The average force exerted on the surface in 30 min is
- (a)
1.2 x 10-4 N
- (b)
1.2 x 10-7 N
- (c)
1.2 x 10-6 N
- (d)
1.2 x 10-5 N
An electromagnetic radiation falls normally on a reflecting surface. If energy of the radiation in 10 s is U, the magnitude of average force imparted to the surface is (c is speed of light)
- (a)
\(\frac{Uc}{50}\)
- (b)
\(\frac{U}{10c}\)
- (c)
\(\frac{U}{5c}\)
- (d)
\(\frac{5U}{c}\)
The rms value of the electric field of the light coming from the sun is 720 NC-1. The average total energy density of the electromagnetic wave is
- (a)
4.58 x 10-6 Jm-3
- (b)
6.37 x 10-9 Jm-3
- (c)
81.35 x 10-12 Jm-3
- (d)
3.3 x 10-3 Jm-3
Which of the following are not electromagnetic waves?
- (a)
Cosmic rays
- (b)
\(\gamma -rays\)
- (c)
\(\beta -rays\)
- (d)
X-rays