Physics - Electromagnetic Waves
Exam Duration: 45 Mins Total Questions : 30
A broadcasting station transmits radio waves of wavelength 300 m. What is the inductance of an inductor that could be connected with a 2.40-\(\mu\)F capacitor to be in resonance with these waves?
- (a)
3.3 \(\times\) 10-2 H
- (b)
3.3 \(\times\) 10-8 H
- (c)
3.3 \(\times\) 10-5 H
- (d)
1.04 \(\times\) 10-8 H
A viberating electric charge radiates
- (a)
electric waves
- (b)
magnetic waves
- (c)
both (a) and (b)
- (d)
light waves
Choose INCORRECT statement :
- (a)
Optics is the branet of electromagnetism
- (b)
The speed of electomagnetic waves depends only on electric and magnetic properties of the medium they travel in, and not on the amplitudes of field variations.
- (c)
Displacement current is NOT a current in the real sense.
- (d)
Without displacement current, the electromagnetic radiation would have been possible.
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.
Temperature required for infrared radiation is of the order of
- (a)
3000 K
- (b)
6000 K
- (c)
9000 K
- (d)
12000 K
Energy of 14.4 keV corresponds to which part of the electromagnetic spectrum
- (a)
Microwaves
- (b)
Radiowaves
- (c)
Gamma ray
- (d)
X-ray
An electric charge in uniform motion produces
- (a)
an electric field only
- (b)
a magnetic field only
- (c)
both electric and magnetic fields
- (d)
electromagnetic waves
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 waves are
- (a)
affected by electric field
- (b)
affected by magnetic field
- (c)
not affected by electric and magnetic field
- (d)
both (a) and (b).
The ratio \(\frac { { E }_{ 0 } }{ { B }_{ 0 } } \) is
- (a)
\(\sqrt { \frac { { \mu }_{ 0 } }{ { \epsilon }_{ 0 } } } \)
- (b)
\(\sqrt { \frac { { \epsilon }_{ 0 } }{ { \mu }_{ 0 } } } \)
- (c)
\(\sqrt { { \mu }_{ 0 }{ \epsilon }_{ 0 } } \)
- (d)
\(\frac { 1 }{ \sqrt { { \mu }_{ 0 }{ \epsilon }_{ 0 } } } \)
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)
\(\sqrt { \frac { \mu \epsilon }{ { \mu }_{ 0 }{ \epsilon }_{ 0 } } } \)
Which of the following elecromagnetic waves has the largest frequency?
- (a)
X-rays
- (b)
ultraviolet rays
- (c)
microwaves
- (d)
gamma rays
The elecromagnetic waves used in telecommunication are
- (a)
U.V. rays
- (b)
Infrared rays
- (c)
Microwaves
- (d)
Visible light rays
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
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
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 phase of velocity (vp) of travelling wave is
- (a)
\({ v }_{ p }=\frac { \omega }{ k } \)
- (b)
\({ v }_{ p }=\frac { d\omega }{ dk } \)
- (c)
\({ v }_{ p }=c\)
- (d)
\({ v }_{ p }=\frac { c }{ { v }_{ g } } \)
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 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 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
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
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
One requires 11 eV of energy to dissociate a carbon monoxide molecule into carbon and oxygen atoms. The minimum frequency of the appropriate electromagnetic radiation to achieve the dissociation lies in
- (a)
visible
- (b)
infrared region
- (c)
ultraviolet region
- (d)
microwave region
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)
\(\frac{5U}{c}\)
An electromagnetic wave propagating along X-direction having wavelength 12 nm. The electric vibration has its maximum amplitude 66 Vm -1. The equation representing the electromagnetic wave is
- (a)
\(66\sin { 5\pi \times { 10 }^{ 16 }\left( t-\frac { x }{ c } \right) } \)
- (b)
\(66\sin { 2\pi \times { 10 }^{ 16 }\left( t-\frac { x }{ c } \right) } \)
- (c)
\(66\sin { 5\pi \times { 10 }^{ 7 }\left( t+\frac { x }{ c } \right) } \)
- (d)
\(66\cos { 5\pi \times { 10 }^{ 7 }\left( t-\frac { x }{ c } \right) } \)
Match the laws given in column I with their exact formula given in column II and select the correct options from the choices given below
Column I | Column II |
A. Gauss's law for magnetism | 1. \(\oint { B.dI={ \mu }_{ 0 }i+{ \varepsilon }_{ 0 }{ \mu }_{ 0 }\frac { d\phi }{ dt } } \) |
B. Ampere's law | 2. \(\oint { E.dI= } -\frac { d\phi }{ dt } \) |
C. Faraday's law | 3. \(\oint { B.ds } =0\) |
- (a)
A B C 2 1 3 - (b)
A B C 3 2 1 - (c)
A B C 1 2 3 - (d)
A B C 3 1 2
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)
The magnetic field in a travelling electromagnetic wave has a peak value of 20nT. The peak value of electric field strength is
- (a)
3 V/m
- (b)
6 V/m
- (c)
9 V/m
- (d)
12 V/m