PHY PUC 2 Notes-Electromagnetic waves

PHY PUC 2 Notes-Electromagnetic waves

1. 08.Electromagnetic Waves



Page145

In previous topic we have learns electric current passes through the conductor
creates magnetic field around it. Also magnetic field changing with time can produces an
electric field . Hence the question arises that whether changing electric field can produce an
magnetic field?
James Maxwell gives the explanation to how changing electric field can produce
magnetic field.
 He concluded that electric and magnetic field are dependent on time and propagate
through space as transverse wave called as electromagnetic waves.
 The electromagnetic waves travel with speed of light.
 Also light is also an electromagnetic wave.
 Hertz conducted the experiment to produce small frequency electromagnetic waves.
 Jagdish chandra Bose also conducted experiments to produce EM waves.
 Marconi successfully produced an EM waves transmitted over long distances.
Hence he is known as father of modern communication.

 Displacement current(??????
??????
)
It is the current which comes into existence in addition to the conduction
current, whenever the electric field and hence electric flux changes with time.
??????
??????=??????
??????
??????∅
??????
????????????

Maxwell’s Equations
1) Gauss law of electrostatic----------------------------------------


2) Gauss law of Magnetism-----------------------------------------


3) Faraday law of electromagnetic induction---------------


4) Modified Ampere Circuital law-------------------------

∮??????⃗⃗ .??????�⃗⃗⃗⃗⃗ =
�
??????
�


∮�⃗⃗ .??????�⃗⃗⃗⃗⃗ =�
??????=−
??????
??????�
[∮�⃗⃗ .??????�⃗⃗⃗⃗⃗ ]

∮�⃗⃗ .??????�⃗⃗⃗⃗⃗ =�
�[??????
�+??????
�
??????∅
??????
??????�
]

2. 08.Electromagnetic Waves



Page146

ELECTROMAGNETIC WAVES
 Source of electric field---- Static charge
 Source of magnetic field------ Moving charge
 Source of Electromagnetic waves---- Accelerated Charge(1mark)
Definition: Electromagnetic wave is a wave which travel through space in the form of
oscillating electric and magnetic field perpendicular to each other in the direction of
propagation of
wave.

Displacement of electric field vector(E) and magnetic field vector(B) is given by
??????⃗⃗ =??????
�??????????????????(??????�−�??????)
�⃗⃗ =�
�??????????????????(??????�−�??????)
Where, ??????=
�??????
�
and �=
�??????
�
also
??????
�
=�
??????
???????????????????????? ??????
?????? are amplitude of electric field and magnetic field
Note: The ratio of ??????
� ??????�?????? �
� is speed of light.
??????
�
�
�
=� ??????��� �=
�
√�
�??????
�


Z
Y
E
E
E E B
B
B
B
E-Electric field component B-Magnetic field component
X

3. 08.Electromagnetic Waves



Page147

 Properties of Electromagnetic Waves(2/3/5 marks)
 Electromagnetic waves are transverse in nature.
 They travel with speed of light.
 EM waves can be polarized, reflected and refracted.
 EM waves do not deflected by electric field neither by magnetic field.
 EM waves obeys the principle of superposition.
 Energy of the electromagnetic wave is given by �=
�
�
[??????
�
(??????
�
)
�
+
(��)
�
�
�
]
 They transport linear momentum on the surface on which they incident,
??????=
�
�

Radiation pressure(Pr):When the EM waves fall on the surfaces it exerts pressure on the
surface called radiation pressure.
??????
�=
??????
�

Where I= intensity of radiation in(Watt/m
2
)

ELECTROMAGNETIC SPECTRUM
The orderly distribution of the electromagnetic waves in accordance with their
wavelength or frequency into distinct groups having widely different properties is called as
EM spectrum.

Solve numerical number 8.2, 8.3 and 8.4 from NCERT
Book

4. 08.Electromagnetic Waves



Page148

CHARACTERISTICS AND APPLICATIONS OF ELECTROMAGNETIC WAVES
EM Waves Frequency Wavelength Application
GAMMA RAYS 10
18
to 10
22
Hz <10
-3
nm
 In radiotherapy for treatment of
cancer
 To initiate some nuclear
reaction.
 To study the structure of atoms
 To preserve food stuffs for
longer time.
X-RAYS 10
16
to 10
19
Hz
1nm
To
10
-3
nm
 In medical diagnosis
 In study of crystal structure
 In detecting cracks in metals
 To detect explosive, diamonds
 To cure skin diseases
UV-RAYS 10
16
to 10
17
Hz
400nm
To
1nm
 In food preservation
 To study the invisible writings,
finger prints
 To study molecule structure
 Cleaning purpose in lab
VISIBLE LIGHT
4x10
14
to
7x10
14
Hz
700nm
To
400nm
 To see the colorful world around
us
 To initiate photosynthesis
reaction in plant to their own
food
INFRA RED
WAVES
10
11
to
5x10
14
Hz
1mm
To
700nm
 In remote control of TV , VCR
 In green house to keep warm
 To know molecule structure
 Infrared lamps to treat muscular
complaints
 In reading secret writings from
ancient wall.

MICRO WAVES 10
9
to 10
12
Hz
0.1m
To
1mm
 In radar system of aircrafts
 In long distance communication
 In microwave Oven for cooking
RADIO WAVES 10
4
to 10
8
Hz >0.1m
 In radio and Television
communication
 In radio astronomy