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1f properties of light eng
1. Optics
Course
Physics 2
Prof. Kamal Abd El-Kader
Physics department, faculty of science,
suez canal university Ismailia Egypt.
kamalmarei@yahoo.com
2.
3. Physics is a science that deals with matter
and energy and their interactions
4. Fundamental Forces of the Universe
There are four fundamental forces in
nature
1- Electromagnetic Force
2- Gravitational Force
3- Nuclear Force
4- Weak Force (radioactive decay)
5. Electromagnetism
Electromagnetism is a branch of Physics, that deals
with the electromagnetic force that occurs between
electrically charged particles.
• The operation of most technological devices is based on
electromagnetic forces.
6. The Electromagnetic Connection
• A changing magnetic field produces an electric
field, and a changing electric field produces
a magnetic field.
• Electric force and Magnetic force both can create
Electromagnetic force.
• An accelerating charge produces electromagnetic
waves
• Both electric and magnetic fields can transport
energy
7. In this course we are going to discuss the
fundamental concepts of electromagnetism:
Electromagnetism
Optics
Electricity
Magnetism
8. Nature of light
Electromagnetic wave theory of light
Quantum theory of light
Wave- Particle Duality of light
9. Properties of the wave
1-amplitude 2- wavelength 3-frequency
Wave train
v = × f
10.
11. • In the 1860’s, Maxwell developed
a mathematical model of electromagnetism.
• He was able to show that these
electromagnetic waves travel at the speed of
light.
• In Wave Theory, light is considered as an Electromagnetic
(EM) Wave.
Electromagnetic wave theory of light
12. • This EM wave consists two components which
are Electric field (E) and Magnetic field (H) which
oscillate and perpendicular to each other as well
as to the direction of wave propagation as shown
in Figure 1
Properties of electromagnetic waves
13. • Electromagnetic waves are transverse waves .
• All electromagnetic waves travel at the same speed equal
to 3x108 m/s in a vacuum and it changes when it travels
from one medium to another.
• Electromagnetic waves carry energy and the amount of
energy carried depends on the wavelength:
the shorter the wavelength, the higher its energy.
• Electromagnetic waves could diffract , interfere and
polarize .
• Electromagnetic waves are not deflected by electric and
magnetic fields.
14. • The electromagnetic spectrum consists of 7 regions
• These regions are
• They are generally in the frequency range from 500 kHz to
about1000 MHz.
• They are used in radio and television communication systems.
1-RADIOWAVES :
Microwaves
15. Microwaves lie between the radio wave and IR portions of the
electromagnetic spectrum.
Microwaves are a form of electromagnetic radiation with
wavelengths ranging from 1m to 1mm
Microwaves are used in radar , communication and in microwave
oven to cook food
2-MICROWAVES:
Microwaves
16. Infrared light lies between the visible and microwave portions of
the electromagnetic spectrum.
3-INFRARED WAVES:
Infrared is divided into 3 spectral regions:
Near-infrared 0.75 -1.5 m,
mid-infrared 1.5-4 m and
far-infrared 4 -1000 m.
Infrared radiation is emitted by any object that has a temperature
Microwaves
17. 4-Visible light
Visible
Red
650 nm
Green
530 nm
Blue
470 nm
Orange
600 nm
Violet
400 nm
Yellow
580 nm
It is the part of the electromagnetic spectrum that is detected by
the human eye.
18. 5-ULTRAVIOLET RAYS:
Ultraviolet light lies between the visible and x-ray portions of the
electromagnetic spectrum.
It consists of 3 region
UV-C 100-280 nm , UV-B 280-315 nm UV-A- 315-400 nm
19. 6-X-RAYS:
X-ray lies between UV and gamma rays portions of the
electromagnetic spectrum.
Most X-rays have a wavelength ranging from 10 pm to 10nm,
20. (1) Gamma ray () is a penetrating form of high-
energy electromagnetic radiation arising from the
radioactive decay of atomic nuclei.
(2) They are used in medicine to destroy cancer
cells.
7-GAMMA RAYS:
21. • In 1900, Max Planck assumed that light is propagated in the form
of packets of energy called quanta. Each quanta of light also
called photon and it has energy
•
E = h ν
Where, ν = Frequency of light, h = Plank’s constant
• Photon is a very tiny little particle that has energy and movement
(momentum) but it has no mass or electrical charge.
Quantum theory of light
22. • in 1905, Albert Einstein used Planck’s idea to explain the
photoelectric effect to support the particle behavior of
light and came out with a QUANTUM THEORY.
• According to Einstein, Photon is considered as discrete
Packet of Energy (Quantum).
• Photon is a very tiny small particle that couldn’t see by
eyes Photon = Packet of Energy = Wave Packet
Einstein's work on wave theory
23. • When photons interact with atom the electrons absorb the
energy (absorption process).
• Photon has no mass and electrical charge.
• Photon travels at the speed of light in vacuum; c= 3x108 m/s
• Photon has a wavelike character that determines its localization
properties in space and time, and the rules by which it interferes
and diffracts.
• Photon carries electromagnetic energy, E and momentum, p
Light is a special kind of electromagnetic energy with
a wavelength range from 380-740 nm (visible light)
24. • In 1924, louis victor de Broglie formulated his hypothesis
that all matter has a wave-like nature, he related
wavelength () and momentum (p)
=
ℎ
𝑝
• On macroscopic scales, we can treat a large number
of photons as a wave.
• When light traveling through space, they act like
waves.
• When light interacts with atoms and molecules, they
act like a stream of energy called photons or quanta.
Wave- Particle Duality of light
25. Question 1
Photon in a blue light have a wavelength of 500nm.
What is the energy of this photon?
According to quantum theory,
a photon has an energy, E given by;
E = hc/λ (unit: Joule,J)
Where, h = Planck’s Constant = 6.625 x 10-34 J/s
c = velocity of light = 3 x 108 m/s
λ = wavelength of light (in meter)
(answ: E = 3.97 x 10-19 J ,
26. Properties of ordinary light
Polychromatic:
Ordinary light consists of many
wavelengths of light such as
mercury vapour lamp
Directionality :
Ordinary light spreads in all
directions
Incoherence:
In ordinary light the wave
trains of same frequency are in
out of phase .
31. Inverse square law of illumination
The inverse square law defines the relationship between the irradiance from a
point source and distance
The illuminance produced by a point source of light inversely
proportional to the square of the distance from the source.
Mathematically formula:
𝐄 =
𝐈
𝐝𝟐
Where
I = intensity of a point source (cd)
d = distance between source and surface (m)
E = illuminance on that surface (Ix).
32. Example: A lamp has a luminous intensity of 1200 cd and acts as
a point source. Calculate the illuminance produced on surfaces
at the following positions:
(a) At 2 m distance from the lamp,
Know:
I = 1200cd, d1 = 2 m and d2 = 6 m, E = ? Using
𝑬 =
𝑰
𝒅𝟐
𝑬 =
𝟏𝟐𝟎𝟎
𝟐𝟐
=
𝟏𝟐𝟎𝟎
𝟒
= 𝟑𝟎𝟎 𝒍𝒙
33. 𝐄 =
𝐈
𝐝𝟐 cos
Where:
E = illuminance on surface (Ix)
I = intensity of source (cd)
d = distance between source and surface (m)
= angle between direction of flux and the normal
Lambert's Cosine law of illumination state that the luminous
intensity observed from a source is directly proportional to
the cosine of the angle θ between the direction of the incident light
and the surface normal
Mathematically formula
38. Boltzmann’s principle,
a fundamental law of thermodynamics, states that,
when a collection of atoms is at thermal equilibrium,
the relative population of any two energy levels is
given by
𝑁2
𝑁 1
= 𝑒
−
𝐸2−𝐸1
𝑘𝑇
N2, N1 are the population of the upper and lower energy
states respectively, T is equilibrium temperature, k
Boltzmann, s constant.
39. 2- Einstein's Quantum Theory of Radiation
Einstein proposed the following assumptions:
• The atom population densities N1 and N2 at energy levels E1 and
E2, respectively, are distributed according to the Boltzmann
distribution at that temperature.
• Population densities N1 and N2 are constant in time.
According to Einstein, the interaction of radiation with matter
could be explained in terms of three basic processes:
a- Absorption
b-Spontaneous Emission,
c Stimulated Emission
40. a-photons of energy h = E2 – E1 is incident on matter with
ground-state energy E1 , Excited state energy E2.
The resonant photon energy h raises the atom from energy
state to E2 .
In the process, the photon is absorbed.
a-Absorption,
41. The rate at which N1 atoms are raised from energy level
E1 to E2 is given by
Where the coefficient B12 is a constant characteristic of the
atom.
ρ (υ) is a factor represented the photon density as
a function of frequency.
1
12
.
1
N
B
dt
dN
abs
42. b-Spontaneous Emission,
• In this process, when an atom in an excited state E2
spontaneously gives up its energy and falls to E1, a photon
of energy h = E2 - E1 is emitted.
• The photon is emitted in a random direction.
43. The rate at which N2 atoms are decreased from energy
level E2 to E1 is given by
𝒅𝑵𝟐
𝒅𝒕 𝒔𝒑𝒐𝒏𝒕
= −𝑨𝟐𝟏𝑵𝟐
• The N2 population decreases with a time constant =
1/A21,
• The constant is referred to as the spontaneous
radiative lifetime of level E2;
• the coefficient A21 is referred to as the radiative rate.
The coefficient A21 is a constant, characteristic of the
atom.
44. Stimulated Emission
When an incident photon of resonant energy h = E2 – E1
passes by an atom in excited state E2,
it stimulates the electron to drop to the lower state, E1 and two
photons in the same direction are emitted
45. The rate at which the N2 atoms are stimulated by the photons is
proportional both to the number of atoms present and the
density of the radiation field
𝒅𝑵𝟐
𝒅𝒕 𝒔𝒆
= −𝑩𝟏𝟐𝑵𝟏𝝆 𝝂
for the Boltzmann distribution of atoms between the two energy
levels
𝑵𝟐
𝑵𝟏
= 𝒆
−
𝑬𝟐−𝑬𝟏
𝒌𝑻 = 𝒆−
𝒉𝝂
𝒌𝑻
that the rates
dN2/dt = N2B21p ()
and
dN1/dt = N1 B12p ()
