Nature of Light
What is light?
Light is radiant energy, usually
referring to electromagnetic
radiation that is visible to the
human eye, and is responsible
for the sense of sight.
In 1643-1727 Sir Isaac Newton
discovered that light coming from
the Sun pass through a Glass prism
will result into a formation of
different colors In the rainbow.
And this stream of Particles he calls
it COSPUSCLES.
At the dawn of 21th century, a
Modern well-known scientist, have
learned through experimentation
that light behaves like a particle at
times, and like a wave at other
times. The particlelike features are
called photons…
And this photons travel on a constant
speed of 300,000 km/sec
(186,000 mi/sec)
Theory of Electromagnetic wave
theory
 theorized that this mutual
generation and
propagation of electric
field and magnetic field
can be conceived as a
form of moving energy
carried by what he called
as electromagnetic wave.
JAMES CLERK MAXWELL
Theory of Electromagnetic wave
theory
 a German physicist who applied
Maxwell’s theories to the
production and reception of
radio waves. The unit of
frequency of a radio wave - one
cycle per second - is named the
hertz
Heinrich Hertz
Theory of Electromagnetic wave
theory
 His contributions to electrical
engineering and electrochemistry
or due to the fact that he was
responsible for introducing the
concept of field in physics to
describe electromagnetic
interaction are enough for him to
be highly recognized.
 Inventor of the Motor, Generator,
And transformer Electromagnetic
Induction.
Michael Faraday
Theory of Electromagnetic wave
theory
 made the revolutionary discovery that
a wire carrying electric current can
attract or repel another wire next to it
that’s also carrying electric current.
The attraction is magnetic, but no
magnets are necessary for the effect
to be seen.
 He went on to formulate Ampere’s
Law of Electromagnetism and
produced the best definition of
electric current during his time.
Andre-Marie Ampere
Theory of Electromagnetic wave
theory
a Danish physicist and chemist
who discovered that the electric
current in a wire can deflect a
magnetized compass needle, a
phenomenon the importance of
which was rapidly recognized and
which inspired the development
of electromagnetic theory.
Hans Christian Oersted
Hans C. Oersted’s experiment
The Basic Principles of EM Wave
Theory

After years of rigorous studies and experiments, the following principles came about to
explain the Electromagnetic Wave Theory.

1. Many natural phenomena exhibit wave-like behaviors. All of them – water waves,
earthquake waves, and sound waves require a medium to propagate. These are examples of
mechanical waves.
 2. Light can also be described as a wave – a wave of changing electric and magnetic fields
that propagate outward from their sources. These waves, however, do not require a medium
to propagate.
 3. They propagate at 300,000,000 meters per second through a vacuum.
 4. Electromagnetic waves are transverse waves. In simpler terms, the changing electric and
magnetic fields oscillate perpendicular to each other and to the direction of the propagating
waves.

These changing electric and magnetic fields generate each other through Faraday’s Law of
Induction and Ampere’s Law of Electromagnetism. These changing fields dissociate from the
oscillating charge and propagate out into space at the speed of light.

5. When the oscillating charge accelerates, the moving charge’s electric fields change, too.
 Albert Einstein (1879-1955)
Light as a Wave…
 Parts of a wave:
 Depending on the frequency, Light waves can be set on a
specific spectrum like:
1.
2.
3.
4.
Micro-waves
X-rays
Ultraviolet rays
Gamma Waves
Interfence
 It is a phenomena where as two or more wavelengths
overlap in space and this is called SUPERPOSITION.
 There are TWO TYPES OF INTERFERENCE
1. CONSTRUCTIVE INTERFERENCE
2. DESTRUCTIVE INTERFERENCE
Diffraction
 Phenomenon were light waves bend around an obstacle
Polarization
 is a property of waves that can oscillate with more than
one orientation. Electromagnetic waves, such as light,
and gravitational waves exhibit polarization
 Light as a RAY
Reflection
 Reflection: is incident on the surface equals the angle at which
it is reflected.
2 types of Reflection
 SPECULAR REFLECTION
- light rays bounce off a
smooth surface and
reflected rays follow a
uniform path
 DIFFUSED REFLECTION
 - Light rays bounce off a
rough surface causing the
light in a non-uniformed
path.
Refraction
 is a phenomenon that often occurs
when waves travel from a medium
with a given reflective material to a
medium with another at an angle
Practice Exercises
 1. the energy emitted by visible light is considered as
bundles of electromagnetic energy called photons. If
a 100W light bulb bas an ave. wavelength of
5.3X10^-7m. How many photons per second does the
light emit?
 2) Microwaves are also used to cook food. If a
microwave oven radiates microwaves with a
wavelength of 2.2cm how much energy does it emit?
 Note: science book (grd10 pg75)
Answers:
 the energy emitted by visible light is considered as bundles of
electromagnetic energy called photons. If a 100W light bulb bas an
ave. wavelength of
5.3X10^-7m. How many photons per second does the light emit?
 Given:
Wavelength (𝜆): 3.3𝑥10−7𝑚
Speed of EM: 3𝑥108 𝑚/𝑠
Frequency: __________Hz
𝑓 = 𝑐/𝜆
𝑓 = 3𝑥108 𝑚/𝑠 ÷ 5.3𝑥10−7 𝑚
𝑡ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒: 𝑡ℎ𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑 𝑜𝑟 ℎ𝑧 𝑡ℎ𝑒 𝑙𝑖𝑔ℎ𝑡 𝑏𝑢𝑙𝑏 𝑒𝑚𝑖𝑡
𝑖𝑠 𝑎𝑏𝑜𝑢𝑡 [5.66𝑥1014 𝐻𝑧.]
Answers:
 Microwaves are also used to cook food. If a microwave
oven radiates microwaves with a wavelength of 2.2cm
how much energy does it emit?
 Given:
Wavelength (𝜆): 2.2𝑐𝑚 → 2.2𝑥10−2 𝑚
Speed of EM: 3𝑥108 𝑚/𝑠
Frequency: __________Hz
Energy : _____________ Joules
𝑓 = 𝑐/𝜆
𝑓 = 3𝑥108 𝑚/𝑠 ÷ 2.2𝑥10−2 𝑚
𝑓 = 1.36𝑥1010 𝐻𝑧
𝐸=ℎ 𝑓
𝐸 = 6.63𝑥10−34 1.36𝑋1010 𝐻𝑧
𝑇ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒 𝑡ℎ𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑒𝑛𝑒𝑟𝑔𝑦 𝑡ℎ𝑒 𝑚𝑖𝑐𝑟𝑜𝑤𝑎𝑣𝑒 𝑒𝑚𝑖𝑡𝑠 𝑖𝑠 𝑎𝑏𝑜𝑢𝑡
[9.01𝑥10−24 𝐽𝑜𝑢𝑙𝑒𝑠] or 5.63125𝑥10−5 eV
The different parts of the spectrum
of light.
Radiowaves (am)
 Radio waves were first
predicted by
mathematical work done
in 1867 by Scottish
mathematical
physicist James Clerk
Maxwell
 Radiowaves have a every low
energy but has a higher
wavelength.
 Radio waves in vacuum travel
at the speed of light. When
passing through a material
medium, they are slowed
according to that
object's permeability and perm
ittivity. Air is thin enough that
in the Earth's atmosphere
radio waves travel very close
to the speed of light.
Radio Broadcasting:
types of Modulation.
AM (amplitude Modulation)
Developed by Lee de Forest
 it was the first method developed
for making audio radio transmissions
but possesses a medium wavelength.
Due to this AM transmissions are
much more susceptible to interference
than FM and digital sounds thus AM
Broadcasting tend to specialize in
spoken-word formats, such as talk
radio, all news and sports.
FM ( Frequency
modulation)
 Invented by Edwin
Armstrong (1933)
 is a broadcasting capable
of better sound than AM
broadcasting
Microwave
 Microwaves travel solely by line-of-sight paths; unlike
lower frequency radio waves, they do not travel as ground
waves which follow the contour of the Earth, or reflect off
the ionosphere (skywaves).Although at the low end of the
band they can pass through building walls enough for
useful reception, usually rights of way cleared to the
first Fresnel zone are required. Therefore, on the surface
of the Earth, microwave communication links are limited
by the visual horizon to about 30–40 miles (48–64 km).
Microwave uses:
 Microwave technology is extensively used for point-topoint telecommunications (i.e. non-broadcast uses).
Microwaves are especially suitable for this use since they
are more easily focused into narrower beams than radio
waves
 Microwaves are used in spacecraft communication, and
much of the world's data, TV, and telephone
communications are transmitted long distances by
microwaves between ground stations and communications
satellites.
 Microwaves are also employed in microwave ovens and
in radar technology.
Infrared:
• Infrared
radiation is electromagnetic
radiation (EMR) with
longer wavelengths than those
of visible light, and is therefore
invisible to the human eye.
• nfrared radiation is popularly
known as "heat radiation", but light
and electromagnetic waves of any
frequency will heat surfaces that
absorb them. Infrared light from
the Sun accounts for 49% of the
heating of Earth, with the rest
being caused by visible light that is
absorbed then re-radiated at longer
wavelengths.
• Frederick William Herschel –
helped to discover infrared.
Visible Spectrum
 The visible spectrum is
the portion of
the electromagnetic
spectrum that is visible to
the human
eye. Electromagnetic
radiation in this range
of wavelengths is
called visible light or
simply light.
 Colors that can be produced by visible light of a narrow
band of wavelengths (monochromatic light) are
called pure spectral colors. The various color ranges
indicated in the illustration are an approximation: The
spectrum is continuous, with no clear boundaries between
one color and the next.
 spectrum into seven named
colors: red, orange, yellow, green, blue, indigo, and violet.
 Spectroscopy is the study of objects based on the
spectrum of color they emit, absorb or reflect.
Spectroscopy is an important investigative tool
in astronomy, where scientists use it to analyze the
properties of distant objects. Typically, astronomical
spectroscopyuses high-dispersion diffraction gratings to
observe spectra at very high spectral
resolutions. Helium was first detected by analysis of the
spectrum of the sun. Chemical elements can be detected in
astronomical objects by emission lines and absorption
lines.
Ultraviolet (UV)
 "Ultraviolet" means "beyond violet" (from Latin ultra,
"beyond"), violet being the color of the highest
frequencies of visible light. Ultraviolet has a higher
frequency than violet light.
 UV radiation was discovered in 1801 when the German
physicist Johann Wilhelm Ritter
 is an electromagnetic radiation with
a wavelength from 10 nm to 400 nm, shorter than
that of visible lightbut longer than X-rays. UV
radiation is present in sunlight constituting about 10%
of the total light output of the Sun.
Practical uses of UV:
mercury-vapor lamps,
Welding tools (electrical arch)
tanning lamps, and black lights
X-ray
 X-ray wavelengths are shorter than those of UV rays and
typically longer than those of gamma rays
 X-radiation is referred to with terms meaning Röntgen radiation,
after the German scientist Wilhelm Röntgen
 X-ray photons carry enough energy to ionize atoms and
disrupt molecular bonds. This makes it a type of ionizing
radiation, and therefore harmful to living tissue. A very
high radiation dose over a short period of time causes radiation
sickness, while lower doses can give an increased risk
of radiation-induced cancer. In medical imaging this increased
cancer risk is generally greatly outweighed by the benefits of the
examination. The ionizing capability of X-rays can be utilized
in cancer treatment to kill malignant cells using radiation therapy
X-ray uses:
Gamma Rays (y)
 Gamma rays (gamma radiation) denoted by the lower
case greek letter Gamma (y) are penetrating
electromagnetic radiation. Paul Villard a French
chemist and physicists discovered gamma radiation in
1900 while studying radiation emitted by radium.
 In 1903 Ernest Rutherford named this radiation
“gamma Rays”.
Natural source of Gamma Radiation:
Quasar
(footnote: defination)
Formula on getting the speed of light
on a Refracting Medium
 N= C / V
 V=C/V
GIVEN:
N= Refracting Medium
C = 3.00 x10^8 m/s (speed of Light in a Vacuum)
V = speed of light in the medium
Sample Problem:
1. What is the speed of light in a 30%sugar
solution?
Given: Nsugar at 30% = 1.38
Speed of light , C =3.00x 10^8m/s
MORE PROBLEMS TO SOLVE:
1. What is the speed of Light in an 80%
sugar solution?
2. What is the Speed of Light in an
Diamond?
3. What is the Speed of Light in an NaCl
Solution?
4. What is the Speed of Light in a Glass of
water at 20’C ?