In 1895, Sir Jagdish Chandra Bose produced electromagnetic waves between 5mm and 25mm in wavelength, but his work remained confined to the laboratory. In 1896, G. Marconi became the first to establish wireless communication across the English Channel at a distance of 48km. In 1901, Marconi succeeded in transmitting signals across the Atlantic Ocean between Newfoundland and Cornwall. He was awarded the 1909 Nobel Prize in Physics for his pioneering work developing wireless telegraphy, telephony, and broadcasting.

9. In 1895, an Indian physicist, Sir Jagdish
Chandara Bose, produced electromagnetic
waves, ranging in wavelengths from 5mm to
25mm. His work, however, remained confined
to laboratory only. In 1896, an Italian
physicist, G. Marconi, became the first to
establish wireless communication when he
transmitted & received signals across English
channel, a distance of about 48km. Later, in
1901, Marconi succeeded in establishing
wireless communication between
Newfoundland & Cornwall, across the Atlantic
ocean. He was awarded the Nobel prize in
Physics in 1909, for his work in developing
wireless telegraphy, telephony &
broadcasting.

10. c= vλ.

11. 5. The velocity (c) of electromagnetic waves in vacuum (i.e. free
space) is given
where μο is the permeability & ο is the permittivity of free
space.
c = 1 = 3 × 108 m/s
√μο ο
6. In a given material medium, the velocity (vm) of
electromagnetic waves is given by
Where μ is the permeability & is the permittivity of
the given medium.
vm = 1
√μ

14. K= 2
λ

16. Most sources of light are classified as incoherent and
unpolarized (or only "partially polarized") because they
consist of a random mixture of waves having different
spatial characteristics, frequencies (wavelengths),
phases, and polarization states. However for
understanding electromagnetic waves and polarization
in particular, it is easiest to just consider coherent
plane waves; these are sinusoidal waves of one
particular direction (or wave vector), frequency,
phase, and polarization state. Characterizing an optical
system in relation to a plane wave with those given
parameters can then be used to predict its response
to a more general case, since a wave with any specified
spatial structure can be decomposed into a
combination of plane waves (its so-called angular
spectrum). And incoherent states can be
modeled stochastically as a weighted combination of
such uncorrelated waves with some distribution of
frequencies (its spectrum), phases, and polarizations.

18. The orderly
distribution i.e.
sequential
arrangement of
electromagnetic waves
according to their
wavelengths or
frequencies in the
form of distinct
groups having
different properties is
called
electromagnetic
spectrum.

24. 1) They are used for insect disinfectatins
for wheat & flour.
2) The γ rays are used for the preservation
of food.
3) The γ rays are used in radiotherapy for
the treatment of cancer & tumor.
4) They are used to produce nuclear
reactions.

25. In 1895, German physicist Wilhelm
Conrad Rontgen discovered X-rays while
studying cathode rays. X-rays are also
called Rontgen rays. These are high
energy electromagnetic waves having
very short wavelengths ranging nearly
from 10-11 m to 10-8 m. When cathode rays
(i.e. fast moving electrons) are suddenly
stopped by an obstacle, X-rays are
produced. X-rays are produced by using
Coolidge X-ray tube in laboratory.

27. 1) X-rays are used to study the structures of
crystals.
2) They are used to distinguish real diamonds, gems
from artificial ones.
3) In surgery, X-rays photographs are useful to
detect bone facture or the presence of foreign
objects like bullets or hidden metal in human
body.
4) X-rays are used to cure skin diseases & to
destroy tumours in the body of patient.
5) They are used to detect flaws or cracks in
metals.
6) They are used for detection of explosives, opium
etc.

30. 1) Ultraviolet rays destroy bacteria & hence they
are used for sterling surgical instruments.
2) Being invisible, ultraviolet rays are used in
burglar alarms.
3) They are used in high resolving power
microscopes.
4) Ultraviolet rays are used in the study of
molecular structure.
5) They are used to distinguish real & false
germs.
6) They are used in the analysis of chemical
compounds.

31. It is the most familiar form of electromagnetic waves. It is the
part of electromagnetic spectrum that is detected by human eye.
These waves are having wavelengths ranging from 4×10-7 m to
8×10-7 m (i.e. frequencies 4×1014 Hz to 8×1014 Hz.) Therefore
this wavelength range is called the visible light. The visible light
is emitted due to atomic excitation. The visible light forms a
narrow part of the electromagnetic spectrum. This light consists
of different colors ranging from red to violet. Different
wavelengths of red color are larger, while those of violet colors
are smaller.

32. Color Wavelength range in ‘m’
Violet 4×10-7 to 4.5×10-7
Blue 4.5×10-7 to5×10 -7
Green 5×10-7 to 5.7×10-7
Yellow 5.7×10-7 to 5.9×10-7
Orange 5.9×10-7 to 6.2×10-7
Red 6.2×10-7 to 7.5×10-7

34. 1. Infrared rays obey the laws of reflection &
refraction.
2. When infrared rays are incident on any
object, the object gets heated.
3. They affect photographic plates.
4. They can produce interference & can be
polarized.
5. These rays are strongly absorbed by glass.
6. They can penetrate through thick
columns of fog & mist.

35. 1) Infrared rays are used in long distance photography.
(Photographs can be taken in complete darkness by
using the infrared film.)
2) They are used in diagnosis of superficial tumours &
varicose veins.
3) They are used to cure infantile paralysis & to treat
sprains, dislocations & fractures.
4) They are used in solar water heaters & solar cookers.
5) Infrared rays are used in medicine.
6) Special infrared photographs of the body, called
thermograms, can show up diseased parts because they
radiate less heat than the healthy parts, which is
sensitive to infrared rays.
7) They are used to keep green house warm.
8) They are used in remote controls of TV, V.C.R. etc.

36. The microwaves are the
electromagnetic waves having
frequencies in the range
5×109 Hz to 1×1012 Hz. The
microwaves are produced by
oscillator electric circuits
(containing a capacitor & an
inductor.) They can be
produced by special vacuum
tubes called klystrons,
magnetrons & Gunn diodes.

37. 1. They obey the laws of reflection &
refraction.
2. They heat an object on which they are
incident.

39. Radio waves are electromagnetic waves having very long
wavelengths ranging from few centimeters to few hundred
kilometers. Like microwaves, radio waves are also produced by
oscillator electric circuits containing an inductor & a capacitor.
The frequency of the waves produced by the circuit depends
upon the magnitude of the inductance & the capacitance. So by
choosing suitable values of the inductance & the capacitance,
microwaves or radio waves of any desired frequency can be
produced.

40. 1. They obey the laws of reflection &
refraction.
2. Radio waves get diffracted from obstacles
coming in their path. The size of the
obstacles should be large as radio waves
are having quite larger wavelengths.

42. Name Frequency
range in Hz
Wavelength
range in m
How produced
γ rays 5×1020 to
3×1018
6×10-13 to
1×10-10
The nuclei of radioactive elements
X- rays 3×1019 to
1×1016
1×10-11 to
3×10-8
Collision of fast moving electrons on
a target of high atomic number
Ultraviolet
rays
1×1016 to
8×1014
3×10-8 to
4×10-7
Excitation of atoms & molecules,
spark
Visible light 8×1014 to
4×1014
4×10-7 to
8×10-7
Excitation of atoms, spark & arc
flame
Infrared rays 4×1014 to
1×1012
8×10-7 to
3×10-4
Excitation of atoms & molecules of
hot bodies
Microwaves 1×1012 to
5×109
3×10-4 to
6×10-2
Oscillator electronic circuits
Radio waves 5×1011 to
8×1010
6×10-4 to
1×105
Oscillator electronic circuits

43. The earth is surrounded by the
atmosphere which extends from the
surface of the earth on an altitude of
about 400 km. The density of air is
maximum close to the earth’s surface &
it decreases as the height above the
earth’s surface increases.(The
composition of air is different at
different levels throughout the
atmosphere.) The atmosphere can be
considered to be having different layers
depending upon temperature changes
which occur from layer to layer. These
layers are given different names. These
layers do not have sharp boundaries,
since there is a gradual transition from
one layer to another.

44. A very important part of the lower atmosphere very close to the
earth’s surface is called the troposphere. It extends from the
earth’s surface to a height about 12km. Most of the water vapour
in atmosphere is present in the troposphere. It is source of the air
that we breath. Dust, smoke, pollen grains, organic materials are
present in it. The temperature ranges from 220K to 280K. The
density ranges from 1.0 to 10-1 kg/m3 which decreases as height
increases.

45. The layer above the troposphere is called the stratosphere. The
air is in the stratosphere contains very little moisture & dust. The
density of air in this layer ranges from 10-1 to 10-3 kg /m3 &
temperature ranges from 220K to 280K. The stratosphere extends
to about 50km above the earth’s surface. The part of the
stratosphere extending from 15km to 50km above the earth’s
surface contains ozone along with the other gases. This part is
called the Ozone layer.

46. The layer above the stratosphere is called the mesosphere,
which extends from 50km to 80km above the earth’s surface. In
this layer the temperature begins to decrease as height increases.
At 80km, the temperature is about 290K to 180K.

47. Ionosphere is the part of atmosphere that extends from 80km to
thousands of km. Beyond the mesosphere, the temperature
begins to rise due to the partial absorptions of solar radiations by
the molecules of air. This layer is called thermosphere. When the
molecules of air absorb solar energy, they emit electrons, so that
neutral molecules of air get converted into positively & negatively
charged particles called the ions. The region of atmosphere
extending from 80km to 400km above the earth’s surface contains
these positive & negative ions. This region is called as
Ionosphere. The ionosphere plays an important role in radio &
telecommunications.

48. It has a large concentration of free electrons & positively charged ions, formed
by the absorption of the UV radiations. X-rays from sun & by collision with
cosmic rays, which strip electrons from molecules & atoms. The ionosphere
reflects back radio waves transmitted by the earth & so is important in radio
communication.
The solar radiation contains ultraviolet rays & the rays of lower
wavelengths along with infrared rays & visible light. The ozone layer in the
atmosphere absorbs the ultraviolet rays of higher frequencies & prevents them
from reaching the earth’s surface. The ozone layer protects the life on the earth
by absorbing the harmful, cancer causing UV radiations coming from sun. In
this way, the ozone layer effectively protects us from the dangerous effects of
solar radiation. Nowadays, rapid industrialization all over the world & the
unnecessary use of fossil fuels has resulted in the release of large quantities of
polluting gases in the atmosphere. Due to this, the amount of ozone in ozone
layer is decreasing. The decrease in the ozone layer may allow the ultraviolet
rays & the rays of still higher frequencies to pass through. This is harmful to the
life on the earth. Immediate steps must be taken to protect the ozone layer so
that the life on earth is protected.

49. Electromagnetic waves in the frequency range of few Hz about
1011 Hz are generally called as the radio waves. These waves
are useful for the transmission of information from one place to
another without the help of wires or any material medium between
the two places. The signal to be transmitted is converted into an
electrical signal & then superimposed on a high frequency
oscillating current flowing through a metallic conductor of suitable
shape & size. This conductor, called the transmitting antenna
radiates the corresponding radio waves into the atmosphere. At
the receiving station, there is another metallic conductor of
suitable shape & size, called the receiving antenna. When the
radio waves are intercepted by the receiving antenna, a small
varying e.m.f. is induced in the antenna. This e.m.f. is amplified &
decoded to obtain the information contained in the original signal.

50. When the radio waves from the transmitting
antenna propagate along the surface of the earth so
as to reach the receiving antenna, the wave
propagation is called ground wave or surface
wave propagation.

52. When the radio waves from the transmitting antenna
reach the receiving antenna either directly or after
reflection from the ground or after reflection from
troposphere, the wave propagation is called space
wave propagation. The radio waves reflected from
troposphere are called tropospheric waves.

54. When the radio waves from the transmitting
antenna reach the receiving antenna either
directly or after reflection in the ionosphere,
the wave propagation is called sky wave
propagation.

55. Radio waves having frequency less than 3 MHz (VH)
are absorbed in the ionosphere, frequencies greater
than 30 MHz {very high frequency [VHF] & ultra high
frequency [UHF]}can pass through the ionosphere after
suffering a small deviation. Radio waves in the high
frequency (HF) bands are totally reflected by the
ionosphere. The frequencies of these waves are
between 3 MHz & 30 MHz . These waves are called the
sky waves. These waves can suffer multiple reflections
between the ionosphere & the earth & therefore they
can be transmitted over large distances.

56. It is the maximum value of the frequency of radio
waves reflected back to the earth from the ionosphere,
when the waves are directed normally to the
ionosphere.

58. Nowadays, TV programmes can be transmitted all over the world
with the help of geostationary satellites. An artificial satellite is raised
to a certain height in an equatorial plane which is projected in a
circular orbit round the earth about its own axis & having a period of
24 hours. So the satellite always appears to be stationary with respect
to earth. The speed of this satellite relative to the earth is zero. Such a
satellite is called the geostationary satellite. It is useful for sending
TV signals over large distances on the earth’s surface. The satellite
receives the signals from the transmitting station, amplifies them &
then sends to the receiving stations on the earth. A TV signal from a
transmitting station can be sent to a receiving station situated on the
diametrically opposite side of the earth with the help of two or more
geostationary satellites. The height of the geostationary satellite above
the surface of the earth is about 36000 km. The satellite is also used in
telecommunications for sending signals over large distances, so it is
also called a communication satellite.

59. communications satellite or comsat is an artificial satellite sent to space for the purpose
of telecommunications. Modern communications satellites use a variety of orbits
including both geostationary (GSO) and non-geostationary (NGSO) orbits, the latter
group which includes Molniya, elliptical and (polar and non-polar) low-Earth orbits.
For fixed (point-to-point) services, communications satellites provide a microwave radio
relay technology complementary to that of communication cables. They are also used
for mobile applications such as communications to ships, vehicles, planes and hand-
held terminals, and for TV and radio broadcasting.

60. 1. Maxwell developed the theory of electromagnetic waves. An
accelerating charge produces electromagnetic waves. E.M. waves
are oscillations that travel through space with the velocity of light.
In an E.M. wave, the electric field vector (E), & the magnetic field
vector (B) oscillate at right angles to each other & also to the
direction of propagation of the wave.
2. Electromagnetic waves with wavelength of the order of few meters
were first produced & detected by Hertz in 1887-1888.
3. Electromagnetic waves have the following properties: Reflection,
Refraction, Inverse square law, Interference, Polarization.
4. Electromagnetic waves carry energy, momentum with them. They
exert pressure on the bodies on which they are incident.
5. The transverse nature of Electromagnetic waves is proved from the
polarization of Electromagnetic waves.

61. 6. This atmosphere consists of different layers at different
heights. The ozone layer absorbs the harmful ultraviolet
rays. The ionosphere is useful in the propagation of sky
waves.
7. There are three modes of propagation of the radio waves.
I. Ground waves: The E.M. waves propagate close to the
ground.
II. Space waves: These E.M. waves travel directly from the
transmitter to the receiver, without being influenced by
the ground.
III.Sky waves: These are the E.M. waves, which reach the
receiving antenna after reflection from the ionosphere.