Electromagnetic Waves PPT Physics Class 12

 Page 1


ELECTROMAGNETIC  WAVES
1. Electromagnetic Waves
2. Properties of Electromagnetic Waves
3. Hertz Experiment
4. Electromagnetic Spectrum 
- Wavelength and Frequency Range
- Sources and Uses
Page 2


ELECTROMAGNETIC  WAVES
1. Electromagnetic Waves
2. Properties of Electromagnetic Waves
3. Hertz Experiment
4. Electromagnetic Spectrum 
- Wavelength and Frequency Range
- Sources and Uses
Electromagnetic Waves:
For a region where there are no charges and conduction current, Faraday’s 
and Ampere’s laws take the symmetrical form:
dF
B
dt
l
E . dl = -
dF
E
dt
l
B . dl = - µ
0
e
0
and
Electric and magnetic fields are sources to each other.
Electromagnetic wave is a wave in which electric and magnetic fields are 
perpendicular to each other and also perpendicular to the direction of  
propagation of wave.
It can also be shown that time – varying electric field produces space –
varying magnetic field and time – varying magnetic field produces space –
varying electric field with the equations:
jB
z
jt
= -
jE
y
jx
and
jE
y
jt
jB
z
jx
= - µ
0
e
0
Page 3


ELECTROMAGNETIC  WAVES
1. Electromagnetic Waves
2. Properties of Electromagnetic Waves
3. Hertz Experiment
4. Electromagnetic Spectrum 
- Wavelength and Frequency Range
- Sources and Uses
Electromagnetic Waves:
For a region where there are no charges and conduction current, Faraday’s 
and Ampere’s laws take the symmetrical form:
dF
B
dt
l
E . dl = -
dF
E
dt
l
B . dl = - µ
0
e
0
and
Electric and magnetic fields are sources to each other.
Electromagnetic wave is a wave in which electric and magnetic fields are 
perpendicular to each other and also perpendicular to the direction of  
propagation of wave.
It can also be shown that time – varying electric field produces space –
varying magnetic field and time – varying magnetic field produces space –
varying electric field with the equations:
jB
z
jt
= -
jE
y
jx
and
jE
y
jt
jB
z
jx
= - µ
0
e
0
Properties of Electromagnetic Waves:
0
X
E
0
B
0
Y
Z
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The electric field vector E and magnetic field vector B are related by       
c = E
0
/ B
0  
where E
0
and B
0
are the amplitudes of the respective fields 
and c is speed of light.
Page 4


ELECTROMAGNETIC  WAVES
1. Electromagnetic Waves
2. Properties of Electromagnetic Waves
3. Hertz Experiment
4. Electromagnetic Spectrum 
- Wavelength and Frequency Range
- Sources and Uses
Electromagnetic Waves:
For a region where there are no charges and conduction current, Faraday’s 
and Ampere’s laws take the symmetrical form:
dF
B
dt
l
E . dl = -
dF
E
dt
l
B . dl = - µ
0
e
0
and
Electric and magnetic fields are sources to each other.
Electromagnetic wave is a wave in which electric and magnetic fields are 
perpendicular to each other and also perpendicular to the direction of  
propagation of wave.
It can also be shown that time – varying electric field produces space –
varying magnetic field and time – varying magnetic field produces space –
varying electric field with the equations:
jB
z
jt
= -
jE
y
jx
and
jE
y
jt
jB
z
jx
= - µ
0
e
0
Properties of Electromagnetic Waves:
0
X
E
0
B
0
Y
Z
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The electric field vector E and magnetic field vector B are related by       
c = E
0
/ B
0  
where E
0
and B
0
are the amplitudes of the respective fields 
and c is speed of light.
4. The velocity of electromagnetic waves in free space, c = 1 / vµ
0
e
0
5. The velocity of electromagnetic waves in a material medium  = 1 / vµe
where µ and e are absolute permeability and absolute permitivity of the 
material medium.
6.  Electromagnetic waves obey the principle of superposition.
7.  Electromagnetic waves carry energy as they propagate through space.   
This energy is divided equally between electric and magnetic fields.
8.  Electromagnetic waves can transfer energy as well as momentum to objects    
placed on their paths.
9. For discussion of optical effects of EM wave, more significance is given to 
Electric Field, E.  Therefore, electric field is called ‘light vector’.
10. Electromagnetic waves do not require material medium to travel.
11. An oscillating charge which has non-zero acceleration can produce     
electromagnetic waves.
Page 5


ELECTROMAGNETIC  WAVES
1. Electromagnetic Waves
2. Properties of Electromagnetic Waves
3. Hertz Experiment
4. Electromagnetic Spectrum 
- Wavelength and Frequency Range
- Sources and Uses
Electromagnetic Waves:
For a region where there are no charges and conduction current, Faraday’s 
and Ampere’s laws take the symmetrical form:
dF
B
dt
l
E . dl = -
dF
E
dt
l
B . dl = - µ
0
e
0
and
Electric and magnetic fields are sources to each other.
Electromagnetic wave is a wave in which electric and magnetic fields are 
perpendicular to each other and also perpendicular to the direction of  
propagation of wave.
It can also be shown that time – varying electric field produces space –
varying magnetic field and time – varying magnetic field produces space –
varying electric field with the equations:
jB
z
jt
= -
jE
y
jx
and
jE
y
jt
jB
z
jx
= - µ
0
e
0
Properties of Electromagnetic Waves:
0
X
E
0
B
0
Y
Z
1. Variations in both electric and magnetic fields occur simultaneously.  
Therefore, they attain their maxima and minima at the same place and at 
the same time.
2. The direction of electric and magnetic fields are mutually perpendicular 
to each other and as well as to the direction of propagation of wave.
3. The electric field vector E and magnetic field vector B are related by       
c = E
0
/ B
0  
where E
0
and B
0
are the amplitudes of the respective fields 
and c is speed of light.
4. The velocity of electromagnetic waves in free space, c = 1 / vµ
0
e
0
5. The velocity of electromagnetic waves in a material medium  = 1 / vµe
where µ and e are absolute permeability and absolute permitivity of the 
material medium.
6.  Electromagnetic waves obey the principle of superposition.
7.  Electromagnetic waves carry energy as they propagate through space.   
This energy is divided equally between electric and magnetic fields.
8.  Electromagnetic waves can transfer energy as well as momentum to objects    
placed on their paths.
9. For discussion of optical effects of EM wave, more significance is given to 
Electric Field, E.  Therefore, electric field is called ‘light vector’.
10. Electromagnetic waves do not require material medium to travel.
11. An oscillating charge which has non-zero acceleration can produce     
electromagnetic waves.
Hertz Experiment:
Induction Coil
Copper or 
Zinc Plate
Metal Rod
Metal Rod
Metal 
Spheres
Ring
P
P S
S
EM 
Wave
Copper or 
Zinc Plate
The copper or zinc 
plates are kept 
parallel separated by 
60 cm.  The metal 
spheres are slided 
over the metal rods to 
have a gap of 2 to 3 
cm.  Induction coil 
supplies high voltage 
of several thousand 
volts.
The plates and the 
rods (with spheres) 
constitute an LC 
combination.
An open metallic ring of diameter 0.70 m having small metallic spheres acts as 
a detector.
This constitutes another LC combination whose frequency can be varied by 
varying its diameter.
S
1
S
2
S
1
’
S
2
’