Electromagnetic_waves.ppsx Notes and everything included

Electromagnetic waves

1. ELECTROMAGNETIC WAVES

2. Maxwell’s Equations
= ………………. Gauss’s law for electricity
= 0 ………………... Gauss’s law for magnetism
= - ……………….. Faradays law
= µ
o
I …………………. Amperes law

3. Failure of Amperes Law
E = =
=
I
I =
=

4. Failure of Amperes Law
Applying Amperes law to surface passing through P
1
B. 2πr = µ
oI
B =
Apply Amperes law to the surface passing through P
B = 0
I
P
1
P
I
P
1
P

5. Failure of Amperes Law – Maxwells Solution
B = 0
I
P
1
E =
Therefore E.A =
But E.A = φ and hence φ =
= =
Or I =
………. DISPLACEMENT CURRENT
Total current = I
c + I
d = I
c +

6. Maxwells Amperes Law
= µ
o
I
c
+ µ
o

= µ
o
I
c

B = µ
oI
c/2πr
Here = µ
oI
c +
B. 2πr = µ
o
(0) + µ
o
= µ
o
I
d
B = µ
o
I
d
/2πr
I
P
1
I
P
1

7. Consequences of Displacement Current
•Laws of electricity and magnetism are far more symmetrical
•Faradays law states that induced emf is equal to the rate of change of flux.
The existence of emf implies the existence of electric field
•Faradays law of electromagnetic induction can also be written as “ A changing
electric field gives rise to a magnetic field and the source of this magnetic
field is the displacement current.
•Thus time dependent electric and magnetic fields give rise to each other. An
important consequence of this symmetry is the existence of electromagnetic
waves

8. Source of Electromagnetic Waves
Accelerating charges produce EM waves
Electric and magnetic field regenerate each other
Frequency of the EM wave = frequency of the oscillating charge.
Energy comes from the source that makes the charge oscillate
Source – AC circuits with specific frequencies (maximum frequency 10
11
Hz)

9. Nature of EM Waves
E
y
= E
o
sin(kx – ωt)
B
z = B
o sin(kx – ωt)
k = 2π/λ , ω = 2π ν
E/B = c
c = 1/õ
oЄ
o in vacuum
v = 1/√µЄ = 1/√Є
rЄ
oµ
rµ
o = c/√Є
rµ
r in any other medium

10. Energy in an EM Wave
E
t
= Energy per unit volume of electric field + Energy per unit volume of magnetic field
E
t
= Є
o
E
2
+ B
2
c = E/B
E
t
= Є
o
E
2
+ )
2
Also c = 1/õ
o
Є
o
.
E
t
= Є
o
E
2
+ µ
o
Є
o
E
t = Є
oE
2
+ Є
oE
2
= Є
oE
2

11. Properties of EM Waves
Velocity of waves in vacuum is c = 1/õ
oЄ
o
No material medium is required for propagation
EM waves carry energy and momentum
EM waves exert pressure which is called as radiation pressure ( P = I/c)
Intensity = Power/Area, Momentum p = Total Energy U/c
All technological applications of EM waves stem from their capability to
carry energy from one place to another

12. Electromagnetic Spectrum

13. Radio Waves
They have the longest wavelength and minimum frequency
Wavelength range : 600m to 0.1m
Frequency range : 500kHz to 1000MHz
Produced due to : Accelerated motion of charges in conducting or oscillating circuits
Uses : 1. Radio and television communication systems
2. Radioastronomy

14. Micro Waves
Wavelength range : 0.3m to 10
-3
m
Frequency range : 10
9
Hz to 10
12
Hz
Produced due to : Oscillating currents in special vacuum tube like klystrons, magnetrons
and Gunn diodes
Uses : 1. Radar systems for aircraft navigation
2. Long distance communication via geostationary satellites
3. Microwave ovens

15. Infrared Waves
Known as heat waves or thermal radiation
Wavelength range : 5 x 10
-3
m to 10
-6
m
Frequency range : 10
11
Hz to 5 x 10
14
Hz
Produced due to : Hot bodies and molecules
Uses : 1. Remote control of TV, radios etc
2. Green houses to keep the plants warm
3. Infrared lamps for treatment of muscle pain
4. In finding the molecular structure of different molecules

16. Visible Waves
Wavelength range : 8 x 10
-7
m to 4 x 10
-7
m
Frequency range : 4 x 10
14
Hz to 7 x 10
14
Hz
Produced due to : Excited atoms in ionized gases
Uses : 1. Provides information of the world around us
2. Can cause chemical reactions

17. Ultraviolet Waves
Wavelength range : 3.5 x 10
-7
m to 1.5 x 10
-7
m
Frequency range : 10
16
Hz to 7 x 10
17
Hz
Produced due to : High voltage gas discharge tubes, sun
Uses : 1. UV lamps are used to kill germs
2. UV rays are focused to a very narrow beam to produce lasers that are used in a
variety of medical applications.
3. Study of molecular structure.

18. X-Rays
Wavelength range : 10
-8
m to 10
-11
m
Frequency range : 10
18
Hz to 10
20
Hz
Produced due to : Sudden deceleration of fast moving electrons by a metal target
Uses : 1. Medical diagnosis for broken bones
2. Study the crystal structure of different materials
3. To detect cracks, flaws in metal products.
4. To detect unwanted items in the security department.
.

19. Gamma-Rays
Wavelength range : 10
-14
m to 10
-10
m
Frequency range : 10
18
Hz to 10
22
Hz
Produced due to : Radioactive nuclei and nuclear reactions
Uses : 1. Treatment of cancer
2. To initiate nuclear reactions
3. To study atomic structure of nuclei.

20. THE END