1. Good Morning
Seniors!!!

2. Let your light shine. Shine
within you so that it can
shine on someone else. Let
your light shine.

3. Theories regarding the
nature of light

4. Light has been characterized by six major
theories over the past 3,000 years. The six
theories are known as:
1. The tactile theory
2. The emission theory
3. The corpuscular theory
4. The wave theory
5. The electromagnetic theory
6. The quantum theory

5. The tactile theory was based on the ability to
touch. The theory stated that the eye sent out
invisible probes to "feel" objects. The
emissions theory, however, was the opposite
of the tactile theory. The emissions theory
stated that bright objects sent out beams or
particles that would ricochet off objects and
enter the eye. The emission theory became
generally accepted over the tactile theory by
the eleventh century.

6. What is a theory?

7. A hypothesis is an educated
guess, based on observation.
Usually, a hypothesis can be
supported or refuted through
experimentation or more
observation. A hypothesis can be
disproven, but not proven to be
true.

8. Example:
If you see no difference in the cleaning
ability of various laundry detergents, you
might hypothesize that cleaning
effectiveness is not affected by which
detergent you use. You can see this
hypothesis can be disproven if a stain is
removed by one detergent and not
another.

9. On the other hand, you cannot prove the
hypothesis. Even if you never see a difference
in the cleanliness of your clothes after trying a
thousand detergents, there might be one you
haven't tried that could be different.

10. A scientific theory summarizes a
hypothesis or group of
hypotheses that have been
supported with repeated testing.

11. A theory is valid as long as there
is no evidence to dispute it.
Therefore, theories can be
disproven. Basically, if evidence
accumulates to support a
hypothesis, then the hypothesis can
become accepted as a good
explanation of a phenomenon.

12. One definition of a theory is
to say it's an accepted
hypothesis.

13. Example:
It is known that on June 30, 1908 in
Tunguska, Siberia, there was an explosion
equivalent to the detonation of about 15
million tons of TNT. Many hypotheses
have been proposed for what caused the
explosion. It is theorized that the
explosion was caused by a natural
extraterrestrial phenomenon, and was
not caused by man.

14. A law generalizes a body of
observations. At the time it is made,
no exceptions have been found to a
law. Scientific laws explain things,
but they do not describe them. One
way to tell a law and a theory
apart is to ask if the description
gives you a means to explain 'why'.

15. Example:
Consider Newton's Law of Gravity.
Newton could use this law to
predict the behavior of a dropped
object, but he couldn't explain why
it happened.

16. http://chemistry.about.com/od/ch
emistry101/a/lawtheory.htm

17. What is light?

18. Light or visible light is
electromagnetic radiation that
is visible to the human eye,
and is responsible for the
sense of sight.

19. Visible light has wavelength in a
range from about 380 nanometers to
about 740 nm, with a frequency range
of about 405 THz to 790 THz. In
physics, the term light sometimes
refers to electromagnetic radiation of
any wavelength, whether visible or
not.

20. What are the theories
regarding the nature of
light?

21. René Descartes
(1596–1650)
held that light was
a mechanical
property of the
luminous body.

22. In 1637 he published a theory of the
refraction of light that assumed,
incorrectly, that light travelled faster in a
denser medium than in a less dense
medium. Descartes arrived at this
conclusion by analogy with the behavior
of sound waves.

23. Although Descartes was incorrect
about the relative speeds, he was
correct in assuming that light
behaved like a wave and in
concluding that refraction could be
explained by the speed of light in
different media.

24. Descartes is not the first to use the
mechanical analogies but because he
clearly asserts that light is only a
mechanical property of the luminous
body and the transmitting medium,
Descartes' theory of light is regarded
as the start of modern physical
optics.

25. Pierre Gassendi (1592–
1655), an atomist,
proposed a particle
theory of light which
was published
posthumously in the
1660s.

26. Isaac Newton studied Gassendi's
work at an early age, and preferred
his view to Descartes' theory of the
plenum. He stated in his Hypothesis
of Light of 1675 that light was
composed of corpuscles (particles of
matter) which were emitted in all
directions from a source.

28. One of Newton's arguments against the wave
nature of light was that waves were known to
bend around obstacles, while light travelled
only in straight lines. He did, however, explain
the phenomenon of the diffraction of light
(which had been observed by Francesco
Grimaldi) by allowing that a light particle
could create a localised wave in the aether.

29. Newton's theory could be used to
predict the reflection of light, but
could only explain refraction by
incorrectly assuming that light
accelerated upon entering a denser
medium because the gravitational
pull was greater.

30. His reputation helped the particle
theory of light to hold sway during
the 18th century.

31. Newton’s corpuscular theory of light is based on the
following points
1. Light consists of very tiny particles known as
“corpuscular”.
2. These corpuscles on emission from the source
of light travel in straight line with high velocity
3. When these particles enter the eyes, they
produce image of the object or sensation of
vision.
4. Corpuscles of different colours have different
sizes.

32. Pierre-Simon
Laplace
The particle theory of
light led Laplace to
argue that a body could
be so massive that light
could not escape from
it. In other words it
would become what is
now called a black
hole.

33. Laplace withdrew his suggestion
when the wave theory of light
was firmly established.

34. In 1672 he discovered
the phenomenon of
diffraction (the
bending of light rays
around corners); to
explain it, he offered
the wave theory of
light.

35. In 1678, Dutch
physicist, Christiaan Huygens,
believed that light was made
up of waves vibrating up and
down perpendicular to the
direction of the light travels,
and therefore formulated a
way of visualizing wave
propagation. This became
known as 'Huygens'
Principle'.

36. According to huygen’s wave theory:
1. Each point in a source of light sends out
waves in all directions in hypothetical medium
called "ETHER".
2. Light is a form of energy
3. Light travels in the form of waves.
4. A medium is necessary for the propagation
of waves & the whole space is filled with an
imaginary medium called Ether
5. Light waves have very short wave length

37. Augustin Fresnel (17881827) elaborated on
Huygens' Principle by
stating that the amplitude
of the wave at any given
point equals the
superposition of the
amplitudes of all the
secondary wavelets at that
point (with the
understanding that the
wavelets have the same
frequency as the original
wave).

38. Thomas Young (13 June
1773 – 10 May 1829)
was an English
polymath. He is
famous for having
partly deciphered
Egyptian hieroglyphics
He was admired by,
among others, Herschel
and Einstein.

39. In Young's own judgment, of his
many achievements the most important
was to establish the wave theory of
light.

40. To do so, he had to overcome the century-old
view, expressed in the venerable Isaac
Newton's "Optics", that light is a particle.
Nevertheless, in the early 19th century Young
put forth a number of theoretical reasons
supporting the wave theory of light, and he
developed two enduring demonstrations to
support this viewpoint

41. With the ripple tank he demonstrated the idea
of interference in the context of water waves.
With the Young's interference experiment, or
double-slit experiment, he demonstrated
interference in the context of light as a wave.

42. James Clerck
Maxwell
(13 June 1831 –
5 November
1879)

43. At the end of the nineteenth century, James
Clerk Maxwell combined electricity,
magnetism and light into one theory. He
called his theory the electromagnetic theory.

44. According to Maxwell, light was an
electromagnetic wave. Because light was an
electromagnetic wave, light carried the same
properties as the other electromagnetic
waves. Maxwell was able to predict the speed
of light by using electrical and magnetic
constants. His calculations proved to be very
close to the accepted value.

45. Max Karl Ernst Ludwig
Planck, (April 23, 1858 –
October 4, 1947) was a
German physicist who
discovered quantum
physics, initiating a
revolution in natural
science and philosophy.
He is regarded as the
founder of quantum
theory, for which he
received the Nobel Prize
in Physics in 1918

46. According to quantum theory
“Energy radiated or absorbed can not have
any fractional value. This energy must be an
integral multiple of a fixed quantity of energy.
This quantity is called “QUANTUM”
OR
Energy released or absorbed is always in the
form of packets of energy or bundles of
energy. These packets of energy are known as
QUANTA or PHOTONS

48. Using Max Planck’s quantum
Theory he formulated the photon
theory of light and explains the
photoelectric effect.

49. In physics, a photon is an
elementary particle, the quantum of
light and all other forms of
electromagnetic radiation, and the
force carrier for the electromagnetic
force.

50. Like all elementary particles, photons are
currently best explained by quantum
mechanics and exhibit wave–particle duality,
exhibiting properties of both waves and
particles.

51. For example, a single photon may be
refracted by a lens or exhibit wave
interference with itself, but also act
as a particle giving a definite result
when its position is measured.

52. Einstein's hypothesis that light
itself is quantized; the quanta of
light are photons.

53. Louis-Victor-Pierre-Raymond, de
Broglie

54. In a thesis published in 1922, when
he was only thirty years old, he
suggested that light could behave
either as a wave or as a steam of

55. He argued that if light which was
normally a form of wave motion
could take on a corpuscular
(particle) form, then small particles
such as electrons could also have
wave-like characteristics associated
with them. However, he had to
wait five years for the evidence.

56. That is all for today!!!

57. Questions???

58. Seatwork!!!

60. Identify the scientist and his
contribution/s in the field of optics.
1.

61. 2.

62. 3.

63. 4.

64. 5.

65. Answers!!!