This document discusses electromagnetic waves and the electromagnetic spectrum. It provides information on the key characteristics of electromagnetic waves including that they do not require a medium, consist of oscillating electric and magnetic fields, and can exhibit properties of both transverse and longitudinal waves. The document also discusses various parts of the electromagnetic spectrum ranging from gamma rays to radio waves and their respective frequency and wavelength ranges. Concepts like wavelength, frequency, speed, intensity, and energy density of electromagnetic waves are defined and their relationships are explained through relevant formulas.

1. Class -12th
PRIYANKA JAKHAR
PHYSICS LECTURER
GGIC VIJAY NAGAR
GHAZIABAD
Electromagnetic waves

2. (Waves)
Mechanical waves Electromagnetic waves
requirement of medium No requirement of medium
Transverse wave Longitudinal wave
Consist no. of patterns of different
frequency
A wave is a physical phenomenon characterized by
its frequency, wavelength, and amplitude. In
general, waves transfer energy from one location to
another, in which case they have a velocity.
A wave is a disturbance that moves energy
from one place to another.
(Waves)

3. Mechanical waves
The waves which
require a material
medium for their
propagation are known
as mechanical waves
Examples
•Water waves
•sound waves
•Spring waves
•waves of the tuning
fork
Electromagnetic Waves
The waves which require no
material medium for their
propagation are
called electromagnetic waves.
These waves propagate out in
space due to the oscillation of
electric and magnetic fields.
examples
•Light waves
•Heat waves
•radio waves
•X-Ray waves

4. medium vibrates at
right angles to the
direction of its
propagation.
the displacement of the
medium is in the same
direction
sound waves.
ultrasound waves.
seismic P-waves
ripples on the
surface of water.
Vibrations in a
guitar string.
एक्स-किरण
radio waves, microwaves, infrared,
visible light, ultraviolet, x-rays, and
gamma rays.

5. Transverse Waves --A wave in which particles of the medium
move perpendicularly to the direction of the wave is called
a transverse wave. Waves that are produced in water are
transverse waves. Observes transverse waves produced by the
up and down movement of a rope.
The highest point of a transverse wave is called crest.
The lowest point between two crests is called Trough.
Longitudinal waves ---A wave in which particles of a medium
move back and forth, parallel to the direction of the wave is
called a longitudinal wave.If we pull and push one end of the
slinky spring continuously, we can produce a longitudinal
wave.
The part of a longitudinal wave, where particles of the medium
are compressed together, are called compressions.
The part of a longitudinal wave, where particles of the medium
are spread out, are called rarefactions.
As the wave moves, compressions and rarefactions are
produced due to the back and forth motion of particles of the
medium. Sound from a vibrating body produces longitudinal

7. (Electromagnetic Wave)
(Electricity) + (magnetism) + (waves)
v=0
Stationary charge
v=uniform Moving charge v=increasing
Acceleratory charge
Electric field
Magnetic field & Electric field
(EMW)

8. According to Faraday's law:-- (1830) Time varying magnetic field creates
changing electric field around it.
According to Oersted:- (1820) when a steady electric current passes
through a wire it creates a magnetic field around it.

9. According to Maxwell :--Analysed that converse of Faraday’s law is
also true.
Time varying electric field creates changing magnetic field around
it.
B E B E B E B
Theory of EMW was mainly developed by Maxwell around
1864.

10. Maxwell's equations:-Maxwell formulated the basis laws of electricity and
magnetism in the form of four fundamental equations.
Gauss's law in electricity
Gauss's law in magnetism
Faraday's law
Ampere -Maxwell law
Ampere's law Maxwell's law
These four equations represent the relationship between electric field, magnetic field, electric
charge and magnetic charge In the absence of any dielectric or magnetic material.

11. •Electric charge q produces an electric field E
•The electric field flux passing through any closed surface is proportional to the total charge contained within
that surface
Gauss's law in magnetism
•The total magnetic flux passing through any closed surface is 0.
•The assumption that there are no magnetic monopoles.
•There are no magnetic flow sources, and the magnetic flux lines always close upon themselves.
•Also called the law of conservation of magnetic flux
Faraday's law
•Changing magnetic flux through a surface induces an electromotive force (EMF) in any boundary path of that
surface.
•A changing magnetic field induces a circulating electric field.
•The voltage accumulated around a closed circuit is proportional to the time rate of change of the magnetic
flux it encloses.
•An electric current I or a changing electric flux through a surface produces a circulating magnetic field
around any path that bounds that surface.
•Electric currents and changes in electric fields are proportional to the magnetic fields circulating about the
areas where they accumulate.
Gauss's law in electricity
Ampere -Maxwell law

12. Displacement current:- Displacement current is the current that is included to explain
the magnetic field inside the capacitor due to mounting up of charges on its plates.
Conduction current:- Conduction current is the electric current that flows through
a conductor because of an applied potential difference.

14. Conduction Current Displacement Current
It is defined as the actual current
produced in the circuit due to the flow of
electrons at an applied voltage.
It is defined as the rate of change of the
electric field between the plates of a
capacitor at an applied voltage.
It is produced due to the flow of charge
carriers (electrons) uniformly whereas
the electric field is constant with time
It is produced due to the movement of
electrons with the rate of change of electric
field
It accepts ohm’s law It doesn’t accept ohm’s law
It is given as I = V/R It is given as
It is represented as actual current
It is represented as apparent current
produced due to the electric field in a
varying time
The difference between conduction current and displacement current include the
following.

15. Maxwell's equations:-

17. is no actual charge transfer in the insulated region between
capacitor which is contradictory to the flow of current. Hence,
displacement current is the current in the insulated region due to
the changing electric flux.
For a charged capacitor, electric field between the plates is given
by:
E= 𝑸 / 𝜺𝒐 ​A
Q= 𝜺𝒐 ∅𝑬
Displacement current is given by:
𝒊𝒅​ =
𝒅𝑸
𝒅𝒕
​= 𝜺𝒐
𝒅∅𝑬
𝒅𝒕
According to Maxwell's Ampere circuital Law, the line integral of
magnetic field along a closed path is equal to μo times the total
current.
∮B.dl= 𝝁𝒐 ​(𝒊𝒄​ ​+ 𝒊𝒅​ ​)
where 𝒊𝒄 ​: Conduction current
𝒊𝒅 ​: Displacement current
∮B.dl= 𝝁𝒐 ​(𝒊𝒄 +𝜺𝒐
𝒅∅𝑬
​)
Displacement current

18. Relation between Displacement current and Conduction current
:- For a charged capacitor, electric field between the plates is given b
E= 𝑸 / 𝜺𝒐 ​A
∅𝑬 = E A
=
𝑸
𝜺𝒐A
​​ A
=
𝑸
𝜺𝒐
Conduction current is given by:
𝒊𝒄 =
𝒅𝑸
𝒅𝒕
Displacement current is given by:
𝒊𝒅 = 𝜺𝒐
𝒅∅𝑬
𝒅𝒕
= 𝜺𝒐
𝒅
𝒅𝒕
​​ (
𝑸
𝜺𝒐
​​ )
=
𝒅𝑸
𝒅𝒕
= 𝒊𝒄

19. (Electromagnetic waves)
1.Electromagnetic waves are propagated by oscillating electric fields and magnetic
field oscillation at right angles to each other.
2.These waves travel with speed 3×𝟏𝟎𝟖ms−1 in vacuum.
3.They are not deflected by electric or magnetic field.
4.They can show interference or diffraction.
5.They are transverse waves.
6.May be polarized.
7.Need no medium of propagation.
8.wavelength and frequency related as c=vλ.
9.The electromagnetic waves being chargeless.

23. Wavelength -A wavelength is the shortest distance between two adjacent crests or
troughs of a transverse wave. For longitudinal waves, it is the distances between
two adjacent compressions or rarefactions.
Wavelength is measured in meter (m).
wavelength in Angstrom unit [ Å ]
1 Å = 𝟏𝟎−𝟏𝟎 m Also,
1 nanometer = l nm = 10-9 m
Frequency -The number of vibrations produced by a vibrating body in one second
is called its frequency.
Frequency is measured in units called hertz (Hz).
When one wave passes in one second its frequency is 1 wave per second or 1
Hertz.

24. The Electric and Magnetic fields in EMR waves are always in phase and at 90
degrees to each other.
In electronic signaling, phase is a definition of the position of a point in time
(instant) on a waveform cycle. A complete cycle is defined as 360 degrees of
phase as shown in Illustration A below. Phase can also be an expression of
relative displacement between or among waves having the same frequency.
Phase

25. Period -The last quantity we will consider is the period of a wave. A wave’s
period is the length of time it takes for one wavelength to pass by a given point
in space. Mathematically, the period (T) is simply the reciprocal of the wave’s
frequency (f):
T= 1 /f,
The units of period are seconds (s).
Amplitude -The amplitude of a wave is the mixture distance of the particles of the
medium from the rest position. We can also say that it is the height of the crest or
depth of a trough (transverse wave) measured from the rest position.
Amplitude is measured in meters (m).

26. Speed, Wavelength, and Frequency
The speed of a wave is a product of its wavelength and frequency.
Because all electromagnetic waves travel at the same speed through
space, a wave with a shorter wavelength must have a higher
frequency, and vice versa. This relationship is represented by the
equation:
Speed = Wavelength × Frequency
The equation for wave speed can be rewritten as:
Frequency=Speed/Wavelength
Wavelength=Speed /Frequency

27. (Momentum):- The momentum of an EM wave is the energy
carried by the wave divided by the speed of light.
If an EM wave is absorbed by an object, or it reflects from an object,
the wave will transfer momentum to the object.
The longer the wave is incident on the object, the more momentum is
transferred.
(Poynting vector):- Poynting vector, a quantity describing the
magnitude and direction of the flow of energy in electromagnetic waves.
S.I. unit is watt per square meter.
It is named after English physicist John Henry Poynting, who introduced
it in 1884.
S = E0 B0 / 2µ0 E = E0 / √2 B= B0 / √2
= E0 E0 / 2cµ0 B0 = E0 /c
= E0
2
/ 2cµ0 c
2
=1 / µ0 ε0
= cE0
2
/
S = cE0
2 ε0/ 2
2c2µ0

28. Intensity of electromagnetic wave :- Intensity generally refers to a
power per area (energy per area per time). For an electromagnetic wave, you can find its
intensity by computing the magnitude of the Poynting vector.
intensity I of an electromagnetic wave is proportional to E2 and B2.
S.I. unit is 𝑾 /𝒎𝟐 .
The energy of electromagnetic wave (U) crossing the area of cross
section at P normally in time Δt is the energy of wave contained in a
cylinder of length c Δt and area of cross section A. It is given by
U = average energy density × Volume of cylinder
U =uav (c Δt) A
The intensity of electromagnetic wave at P is
I = U / A Δt
= uav c Δt A / A Δt
= uav c
In terms of maximum electric field
uav = ε0 E0
2 / 2
so, I = ε0 E0
2 c / 2
= ε0 E2
rms c
In terms of maximum magnetic field
uav = B0
2 / 2μ0
so, I = B0
2 c / 2μ0
= B2
rms c / μ0
where c is the speed of light, ε0 is the permittivity
of free space, and E0 is the maximum electric field
strength
E0/B0= c2
, where μ0 is the permeability of free space.

29. (Energy density) :-electromagnetic waves are three-dimensional, it is usually useful to
discuss the energy density (energy per volume) of an electromagnetic wave. The total energy
density of the electromagnetic wave is equal to the sum of the energy density of the electric field
and the energy density of the magnetic field. Energy density due to electric field UE = E 2
ε0/ 2
Energy density due to magnetic field UB = B 2
/ 2 µ0
आयाम क्रमशः E0 व B0
E = E0 / √2 B= B0 / √2
UE = E0
2 ε0/ 4
UB = B0
2
/ 4 µ0
UE / UB = E0
2 ε0µ0/ B0
2 E0/B0= c2
=c2×1/ c2 ε0µ0 = 1/c2
UE / UB = 1
UE = UB The energy is carried by the

30. Regarding electromagnetic waves, both magnetic and electric field are equally involved in contributing to energy density
Therefore, the formula of energy density is the sum of the energy density of the electric and magnetic field.
UE =
E 2 ε0
𝟐
UB =
B 2
𝟐µ0
𝑼 = 𝑼𝑬 + 𝑼𝑩
𝑼 =
E 2 ε0
𝟐
+
B 2
𝟐µ0

31. (Radiation pressure):- An object absorbing an
electromagnetic wave would experience a force in the
direction of propagation of the wave. The force corresponds
to radiation pressure exerted on the object by the wave.
The force would be twice as great if the radiation were
reflected rather than absorbed.
perfectly absorbing
perfectly reflecting

32. Hertz experiment
The existence of electromagnetic waves was confirmed experimentally by Hertz in 1888.
This experiment is based on the fact that an oscillating electric charge radiates
electromagnetic waves. The energy of these waves is due to the kinetic energy of the
oscillating charge.
It consists of two metal plates A and B placed at a distance of 60 cm from each other. The
metal plates are connected to two polished metal spheres S1 and S2 by means of thick
copper wires. Using an induction coil a high potential difference is applied across the small
gap between the spheres.
s

33. Due to high potential difference across S1 and S2, the air in the small gap between the
spheres gets ionized and provides a path for the discharge of the plates. A spark is produced
between S1 and S2 and electromagnetic waves of high frequency are radiated. Hertz was
able to produce electromagnetic waves of frequency about 5 × 107 Hz.
Here the plates A and B act as a capacitor having small capacitance value C and the
connecting wires provide low inductance L. The high frequency oscillation of charges
between the plates is given by

34. (Electromagnetic spectrum) The electromagnetic (EM) spectrum is the range of all types
of EM radiation. Radiation is energy that travels and
spreads out as it goes – the visible light that comes from a
lamp in your house and the radio waves that come from a
radio station are two types of electromagnetic radiation.
The other types of EM radiation that make up the
electromagnetic spectrum are microwaves, infrared
light, ultraviolet light, X-rays and gamma-rays.

36. Gadi X U V In My Range
Gamma
rays X- ray Ultra-violet
Rays
Visible
Rays
Infra red
Rays
Microwave Radio
waves
How to learn

38. Type of Radiation Frequency Range (Hz) Wavelength
Range
gamma-rays 10
20
– 10
24
< 10
-3
nm
x-rays 10
17
– 10
20
1 nm – 10
-3
nm
ultraviolet 10
15
– 10
17
400 nm – 1 nm
visible 4 – 7.5×10
14
700 nm – 400 nm
infrared 10
13
– 10
14
1mm – 700 nm
microwaves 3×10
11
– 10
13
0.1 m – 1mm
radio waves < 3×10
11
> 0.1 m

39. How to remember
Bade bhai ne Radio ko Koni se Mar kar Gira Diya jisse Chhota bhai hurt Ho Gaya . Red or
Herschel ko ,new Drishya per uv ne writer Se Kaha Aise Rang Khel Ke Bekar Hain.
Radio & TV - marconi - Bade bhai ne Radio ko
Koni se Mar kar Gira Diya
Microwaves - hertz - jisse Chhota bhai hurt Ho Gaya .
Infrared - Herschel - Red or Herschel ko

40. Visible light - newton - new Drishya per
Ultraviolet - Ritter - uv ne writer Se Kaha
X-rays - Roentgen - Aise Rang
Gamma rays - Becquerel - Khel Ke Bekar Hain

41. Radio waves
Radio waves are used for communication such as television and radio. Radio
waves are transmitted easily through air. They do not cause damage if absorbed
by the human body, and they can be reflected to change their direction. These
properties make them ideal for communications.
Microwaves
Microwaves are used for cooking food and for satellite communications.
Infrared
Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras
which detect people in the dark. Security lights and remote controls for TV use infrared waves.
Visible light
Visible light is the light we can see. It is used in fibre optic communications, where coded
pulses of light travel through glass fibres from a source to a receiver.
Ultraviolet
We cannot see ultraviolet (UV) light but it can have hazardous effects on the
human body. Ultraviolet light in sunlight can cause the skin to tan or burn and can
also damage eyes. Fluorescent substances are used in energy-efficient lamps –
they absorb ultraviolet light produced inside the lamp, and re-emit the energy as
visible light.

42. •UV light is also used for banknote security and disinfecting water.
•Most UV-B and all UV-C is absorbed by ozone (O3) molecules in the upper
atmosphere. Consequently, 99% of the solar UV radiation reaching the Earth’s
surface is UV-A.
•An overexposure to UVB radiation can cause sunburn and some forms of skin
cancer.
X-rays
•X-rays have shorter wavelengths (higher energy ) than UV waves and, generally,
longer wavelengths (lower energy) than gamma rays. Sometimes X-rays are called
Röntgen radiation, after Wilhelm Röntgen, who is usually credited as their
discoverer.
•Because X-rays have very high energy they are known as ionizing radiation and
can harm living tissue. A very high radiation dose over a short amount of time
causes radiation sickness, while lower doses can give an increased risk of
radiation-induced cancer.
•Lower doses of X-ray radiation can be very effectively used in medical
radiography and X-ray spectroscopy.
•X-rays are broken up into broad two categories: hard X-rays with energies above

43. •Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and
denoted as γ, is electromagnetic radiation of high frequency and therefore high
energy.
•Gamma rays have characteristics identical to X-rays of the same frequency—they
differ only in source. Gamma rays are usually distinguished by their origin: X-rays
are emitted by definition by electrons outside the nucleus, while gamma rays are
emitted by the nucleus.
Gamma rays

44. Radiation Production Detection Application
Radio waves From oscillating
electrical circuits.
Accelerating charges
Antennae (aerials),
diodes, earphones.
In telecommunication- radio
broadcast, TV and satellite
communication, cellular
telephone, radar and navigation
equipments etc.
Microwaves From special vacuum
tubes called magnetrons
within microwave
ovens.
Accelerating charges
& thermal agitation
Crystal detectors, solid
state diodes, antennae.
Cooking in microwave cookers.
In communication- mobile
phones.
In speed cameras.
Infra red From thermal vibration of
atoms in very hot bodies.
Eg- the sun.
Thermal agitations &
electronic transitions
Thermopile, bolometer,
thermometer,
photographic film.
Heating effect on the
skin.
Burglar alarms, in military night
vision missiles, cooking, heating
and drying of grains, in green
housing, in remote controls for
TVs and VCD/DVDs, in
photography.

45. Visible
light
Sun, hot objects,
lamps, laser beams.
Thermal
agitations &
electronic
transitions
The eye, photographic
film, photocell.
Vision (sight), photography,
photosynthesis and optical fibre. Laser
beams used in laser printers, weapon
aiming systems, CD players.
Ultraviolet The sun, sparks,
mercury vapour
lamps. Thermal
agitations &
electronic
transitions
Photographic film,
photocells,
fluorescent materials
e.g quinine sulphate.
Detection of forgeries, skin treatment
and killing of bacteria, spectroscopy
and mineral analysis, making of clothes
and a source of vitamin D.
X-rays In X-ray tubes
Inner electronic
transitions and
fast collisions
Fluorescent screen
and photographic
film.
Radiography (identification of internal
body structures or bones), cancer
therapy, crystallography (study of
crystal structure), pest and germ

46. Gamma
radiation
Emitted by
radioactive
substances.
Nuclear decay
Radiation detectors
e.g GM tube.
Sterilizing medical equipment and
food.
Killing of cancer cells and other
malignant growths.
Pest control.
Detection of flaws in metals.

47. Waves which are not electromagnetic waves :-
a) Cathode rays
b) X-rays
c) Beta rays
d) Cosmic rays