1. Electromagnetic radiation consists of synchronized oscillations of electric and magnetic fields that travel through space as waves. It includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. 2. The history of electromagnetic theory began with studies of lightning and progressed through the work of scientists like Coulomb, Ampère, Faraday and Maxwell. Maxwell unified electric and magnetic field theories and predicted electromagnetic waves. 3. Maxwell postulated displacement current to account for changing electric fields in capacitors. This led to the generalized Ampere's law and understanding that changing electric fields produce magnetic fields, and vice versa, resulting in electromagnetic waves.

1. Introduction
Electromagnetic radiation is one of the many ways that energy
travels through space. The heat from a burning fire, the light from
the sun, the X-rays used by your doctor, as well as the energy used
to cook food in a microwave are all forms of electromagnetic
radiation. While these forms of energy might seem quite different
from one another, they are related in that they all exhibit wavelike
properties.
Electromagnetic radiation consists of electromagnetic waves,
which are synchronized oscillations of electric and magnetic fields.
Electromagnetic radiation or electromagnetic waves are created
due to periodic change of electric or magnetic field. Depending on
how this periodic change occurs and the power generated,
different wavelengths of electromagnetic spectrum are produced.
In a vacuum, electromagnetic waves travel at the speed of light,
commonly denoted c.

2. History
The history of electromagnetic theory begins with ancient
measures to understand atmospheric electricity, in particular
lightning. Scientific understanding into the nature of electricity
grew throughout the eighteenth and nineteenth centuries through
the work of researchers such as Coulomb, Ampère, Faraday and
Maxwell. In the 19th century it had become clear that electricity and
magnetism were related, and their theories were unified: wherever
charges are in motion electric current results, and magnetism is
due to electric current. The source for electric field is electric
charge, whereas that for magnetic field is electric current (charges
in motion). On November 11, 1886, propagation of an
electromagnetic wave was observed for the first time with the help
of a German physicist Heinrich Hertz.
Heinrich Hertz

3. DISPLACEMENT
CURRENT
We know that an electric current produces a magnetic field around
it. J.C. Maxwell showed that for logical consistency, a changing
electric field must also produce a magnetic field. Further, since
magnetic fields have always been associated with currents,
Maxwell postulated that this current was proportional to the rate of
change of the electric field and called it displacement current. To
determine this, let’s look at the process of charging a capacitor.
Further, we will apply Ampere’s circuital law to find a magnetic
point outside the capacitor.
Figure 1
The figure above shows a parallel plate capacitor connected in a
circuit through which a time-dependent current i(t) flows. We will
try to find the magnetic field at a point P, in the region outside the
capacitor.

4. Consider a plane circular loop of radius r centred symmetrically
with the wire. Also, the plane of the loop is perpendicular to the
direction of the current carrying wire. Due to the symmetry, the
magnetic field is directed along the circumference of the loop and
has similar magnitude at all points on the loop.
Figure 2
However, as shown in the Figure(2) above, when the surface is
replaced by a pot-like surface where it doesn’t touch the current
but has its bottom between the capacitor plates or a tiffin-shaped
surface (without the lid) and Ampere’s circuital law is applied,
certain contradictions arise.
These contradictions arise since no current passes through the
surface and Ampere’s law does not take that scenario into
consideration. This leads us to understand that there is something
missing in the Ampere’s circuital law. Also, the missing term is

5. such which enables us to get the same magnetic field at point P
regardless of the surface used.
If we look at the last figure again, we can observe that the common
thing that passes through the surface and between the capacitor
plates is an electric field. This field is perpendicular to the surface,
has the same magnitude over the area of the capacitor plats and
vanishes outside it.
Hence, the electric flux through the surface is Q/ε0 (using Gauss’s
law). Further, since the charge on the capacitor plates changes
with time, for consistency we can calculate the current as follows:
i = ε0 (dQ/dt)
This is the missing term in Ampere’s circuital law. In simple words,
when we add a term which is ε0 times the rate of change of electric
flux to the total current carried by the conductors, through the
same surface, then the total has the same value of current ‘i’ for all
surfaces. Therefore, no contradiction is observed if we use the
Generalized Ampere’s Law.
Hence, the magnitude of B at a point P outside the plates is the
same at a point just inside. Now, the current carried by conductors
due to the flow of charge is called ‘Conduction current’. The new
term added is the current that flows due to the changing electric
field and is called ‘Displacement current’ or Maxwell’s
Displacement current’. By now we understand that there are two
sources of a magnetic field:
1. Conduction electric current due to the flow of charges
2. Displacement current due to the rate of change of the electric
field

6. Hence, the total current (i) is calculated as follows: (where ic –
conduction current and id – displacement current)
i = ic + id = ic + ε0 (dQ/dt)
This means that –
 Outside the capacitor plates: ic = i and id = 0
 Inside the capacitor plates: ic = 0 and id = i
So, the generalized Ampere’s law states:
“The total current passing through any surface of which the closed
loop is the perimeter is the sum of the conduction current and the
displacement current”.
This is also known as – Ampere-Maxwell Law. It is important to
remember that the displacement and conduction currents have the
same physical effects. Here are some points to remember-
 In cases where the electric field does not change with time,
like steady electric fields in a conducting wire, the
displacement current may be zero.
 In cases like the one explained above, both currents are
present in different regions of the space.
 Since a perfectly conducting or insulating medium does not
exist, in most cases both the currents can be present in the
same region.
 In cases where there is no conduction current but a time-
varying electric field, only displacement current is present. In
such a scenario we have a magnetic field even when there is
no conduction current source nearby.

7. Ampere-Maxwell Law-
When electromagnetic waves propagate in space than electric and
magnetic field oscillate in mutual perpendicular direction.
We know that time varying magnetic field produces electric field.
Maxwell explained that time varying electric field also produces
magnetic field Maxwell formulated a set of equations (Maxwell
questions) involving electric and magnetic field.
Ampere law
∮B.dl=μ0i
Maxwell formed the relation of time varying electric and magnetic
field.
∮B.dl=μ0ε0dϕε/dt
So combination of ampere law
∮B.dl=μ0ε0dϕε/dt+μ0i
μ0(id+i)
id=displacement current i=conduction current
id=ε0dϕε/dt ε0=permittivity

8. Characteristics of
Electromagnetic Waves
As you might already know, a wave has a trough (lowest point) and
a crest (highest point). The vertical distance between the tip of a
crest and the wave’s central axis is known as its amplitude. This is
the property associated with the brightness, or intensity, of the
wave. The horizontal distance between two consecutive troughs or
crests is known as the wavelength of the wave. These lengths can
be visualized as follows:
Keep in mind that some waves (including electromagnetic waves)
also oscillate in space, and therefore they are oscillating at a given
position as time passes. The quantity

9. known as the wave’s frequency refers to the number of full
wavelengths that pass by a given point in space every second; the
SI unit for frequency is Hertz.
As you might imagine, wavelength and frequency are inversely
proportional: that is, the shorter the wavelength, the higher the
frequency, and vice versa.
The electric field varies with time, and it will give rise to a magnetic
field, this magnetic field varies with time and it gives rise to the
electric field and the process continues like this. These electric and
magnetic fields vary periodically and are coupled with each other
when concurrently propagating in space giving rise to
electromagnetic waves.
The magnetic field will be a sine wave but in a direction
perpendicular to the electric field. Both of these provide
advancement to the electromagnetic field. However, the magnetic
field along the y-axis, the wave will also propagate in the z-axis if
the electric field is along the x-axis.
The electric and magnetic fields are each distinct and
perpendicular to the direction of surge propagation. Electric and
magnetic fields that are opposite in time and linked to each other
give rise to electromagnetic waves The electric and magnetic fields
are each distinct and perpendicular to the direction of surge
propagation. Electric and magnetic fields that are opposite in time
and linked to each other give rise to electromagnetic waves.

11. Nature of Electromagnetic
Waves
EM waves are transverse waves. The transverse waves are those
in which the direction of disturbance or displacement in the
medium is vertical to that of the propagation of the wave.
The patches of the medium are moving in a direction vertical to the
direction of propagation of the wave. In the case of EM waves, the
propagation of waves takes place along the x-axis, electric and
magnetic fields are vertical to the wave propagation.
This means surge propagation x-axis, electric field y-axis,
magnetic field z- axis. • Because of this EM waves are transverse
waves in nature. The electric field of EM surge is represented as,
Ey = E0 sin(kx– wt)
Where Ey = electric field along the y-axis and x = direction of
propagation of the wave.
Wave number k = (2π/λ)
The magnetic field of the EM wave is represented as
Bz = B0 sin(kx− wt)
Electromagnetic waves have constant velocity in vacuum and it is
nearly equal to 3×10^8 ms−1
which is denoted by v = 1/√μϵ
Electromagnetic wave propagation does not require any material
medium to travel.

12. The inherent characteristic of an electromagnetic wave is its
frequency. Their frequencies remain unchanged but its wavelength
changes when the wave travels from one medium to another.
Electromagnetic wave follows the principle of superposition.
In an electromagnetic wave, the oscillating electric and magnetic
fields are in the same phase and their magnitudes have a constant
ratio. The ratio of the amplitudes of electric and magnetic fields is
equal to the velocity of the electromagnetic wave. C = E0B0

13. Types of
Electromagnetic Waves
Though the sciences generally classify EM waves into seven basic
types, all are manifestations of the same phenomenon.
• Radio Waves: Instant Communication.
• Microwaves: Data and Heat.
• Infrared Waves: Invisible Heat.
• Visible Light Rays: Light.
• Ultraviolet Waves: Energetic Light.
• X-rays: Penetrating Radiation.
• Gamma Rays: Nuclear Energy.

14. Electromagnetic
Spectrum
The electromagnetic spectrum is the range of frequencies (the
spectrum) of electromagnetic radiation and their respective
wavelengths and photon energies. The electromagnetic spectrum
covers electromagnetic waves with frequencies ranging from
below one hertz to above 1025
hertz, corresponding to wavelengths
from thousands of kilometers down to a fraction of the size of an
atomic nucleus.
This frequency range is divided into separate bands, and the
electromagnetic waves within each frequency band are called by
different names; beginning at the low frequency (long wavelength)
end of the spectrum these are: radio waves, microwaves, infrared,
visible light, ultraviolet, X-rays, and gamma rays at the high-
frequency (short wavelength) end.
The electromagnetic waves in each of these bands have different
characteristics, such as how they are produced, how they interact
with matter, and their practical applications.
The types of electromagnetic radiation are broadly classified into
the following classes (regions, bands or types): Gamma radiation

15. X-ray radiation Ultraviolet radiation Visible light Infrared radiation
Microwave radiation Radio waves.
This classification goes in the increasing order of wavelength,
which is characteristic of the type of radiation. There are no
precisely defined boundaries between the bands of the
electromagnetic spectrum; rather they fade into each other like the
bands in a rainbow (which is the sub-spectrum of visible light).
Radiation of each frequency and wavelength (or in each band) has a
mix of properties of the two regions of the spectrum that bound it.
For example, red light resembles infrared radiation in that it can
excite and add energy to some chemical bonds and indeed must do
so to power the chemical mechanisms responsible for
photosynthesis and the working of the visual system.
electromagnetic radiation interacts with matter in different ways
across the spectrum.
These types of interaction are so different that historically different
names have been applied to different parts of the spectrum, as
though these were different types of radiation. Thus, although
these "different kinds" of electromagnetic radiation form a
quantitatively continuous spectrum of frequencies and
wavelengths, the spectrum remains divided for practical reasons
related to these qualitative interaction differences.

17. 1. RADIO WAVES-Radio waves have the lowest frequencies and
longest wavelengths among EM waves. They are used for
communication, broadcasting, and navigation. Radio waves
can be produced using oscillating electric charges or
magnetic fields, and can be detected using antennas,
wavelength range: > 0.1 m.
2. MICROWAVES-Microwaves have higher frequencies and
shorter wavelengths than radio waves. They are used for
heating, cooking, and communication purposes. Microwaves
can be produced using magnetrons, and can be detected using
parabolic reflectors called dishes, wavelength range: 0.1 mm
to 1 mm.

18. 3. INFRARED WAVES-Infrared waves have shorter wavelengths
than microwaves but longer wavelengths than visible light.
They are used for heating, thermal imaging, and remote
sensing. Infrared waves can be produced when objects emit
heat, and can be detected using thermopiles or photodiodes,
wavelength range: 700 nanometers (nm) to 1 millimeter (mm).
4. VISIBLE LIGHT-Visible light has frequencies that are higher
than infrared waves and lower than ultraviolet waves. It is
used for vision and is essential for life on Earth. Visible light
can be produced using various sources such as stars, LEDs,
and fluorescent bulbs, wavelength range: 400 nm (violet) to
700 nm (red).

19. 5. ULTRAVIOLET WAVES-Ultraviolet waves have higher
frequencies and shorter wavelengths than visible light. They
are used for disinfection, curing of inks and coatings, and in
analytical chemistry. Ultraviolet waves can be produced using
special lamps, and can be detected using photodiodes,
wavelength range: 1 nm to 400 nm. Welders wear special
glass goggles or face masks with glass windows to protect
their eyes from large amount of UV produced by welding arcs.
Due to its shorter wavelengths, UV radiations can be focussed
into very narrow beams for high precision applications such
as LASIK (Laser assisted in situ keratomileusis) eye surgery.
UV lamps are used to kill germs in water purifiers. Ozone
layer in the atmosphere plays a protective role, and hence its
depletion by chlorofluorocarbons (CFCs) gas (such as freon)
is a matter of international concern.

20. 6. X-RAYS-X-rays have the highest frequencies and shortest
wavelengths among EM waves. They are used in medical
imaging, security screening, and materials analysis. X-rays
can be produced using special tubes or synchrotron radiation,
and can be detected using detectors such as film or digital
sensors, wavelength range: 0.01 nm to 10 nm.
7. GAMMA RAYS-Gamma rays have the highest frequencies and
shortest wavelengths among all EM waves. They are used in
medicine, scientific research, and sterilization. Gamma rays
can be produced using nuclear reactions or particle
accelerators, and can be detected using special detectors
such as Geiger counters, wavelength range: below 0.01 nm.
TABLE-

21. Conclusion

22. In conclusion, electromagnetic waves (EM waves) play a
fundamental role in our understanding of the universe and have
widespread applications in various fields. From the theoretical
framework of Maxwell's equations to the practical use in
communication, medicine, and technology, EM waves have
revolutionized the way we interact with and perceive our world. The
ability of these waves to propagate through vacuum and various
mediums, their diverse wavelengths, and the speed at which they
travel make them a versatile tool in scientific research and
everyday life. As technology continues to advance, our
comprehension and utilization of electromagnetic waves will likely
deepen, leading to further innovations and discoveries. The study
and application of EM waves are pivotal in shaping the present and
future of science and technology.
Bibliography

23.  Ncert Physics Textbook for Class XII (Part 1)
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 www.toppr.com
 www.kit.edu
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 www.britannica.com
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 Images from Google Images