1. Light

2. Briefly
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.
Primary properties of light are intensity, propagation direction, frequency or wavelength spectrum, and polarization.
Its speed in a vacuum, 299,792,458 meters per second, is one of the fundamental constants of nature.
The study of light, and the interaction of light and matter is termed optics, is an important research area in modern physics.

3. Light, which is emitted and absorbed in tiny "packets" called photons, exhibits properties of both waves and particles. This property is referred to as the wave–particle duality.

4. Ray Theory – Light travels along a straight line and obeys laws of geometrical optics. Ray theory is valid when the objects are much larger than the wavelength (multimode fibers)

5. Archimedes of Syracuse (Greek: Ἀρχιμήδης)
Dossier of History
Archimedes of Syracuse (Greek: Ἀρχιμήδης)
Born
c. 287 BC Syracuse, Sicily; Magna Graecia
Died
c. 212 BC (aged around 75) Syracuse
Residence
Syracuse, Sicily
Fields
Mathematics, Physics, Engineering, Astronomy, Invention
Known for
Archimedes' Principle, Archimedes' screw, Hydrostatics, Levers, Infinitesimals

6. Ptolemy (Batlamyus)
Born
c. AD 90; Egypt
Died
c. AD 168 (aged 77–78) Alexandria, Egypt
Occupation
mathematician, geographer, astronomer, astrologer

7. Law of reflection the angle of incidence equals angle of reflection
angles are measured from normal

8. Refraction Snell’s Law
index of refraction, n, where c = speed of light in a vacuum and v = speed of light in that medium
nair = 1
nglass = 1.5
Snell’s Law

9. Total Internal Reflection
Incident angle where refracted angle (2) is 90 is the critical angle
at incident angles greater than critical angle, light is totally internally reflected
Geometric Optics

10. Guided Propagation Along the Optical Fiber
The structure of a typical single-mode fiber. 1. Core: 8 µm diameter 2. Cladding: 125 µm dia. 3. Buffer: 250 µm dia. 4. Jacket: 400 µm dia.

11. Plato’s fire
Full name
Plato (Πλάτων)
Born
c. 428–427 BC; Athens
Died
c. 348–347 BC (age approx 80); Athens
Era
Ancient philosophy
Region
Western Philosophy
School
Platonism
Influenced by: Socrates, Homer, Hesiod, Aesop, Protagoras, Parmenides, Pythagoras, Orphism, …
Influenced: Most of subsequent western philosophy, including Aristotle, Augustine, Neoplatonism, Cicero, Plutarch, Stoicism, Anselm, Machiavelli, Descartes, Hobbes, Leibniz, Mill, Schopenhauer, Nietzsche, Heidegger, Arendt, Gadamer, Imam Khomeini, Russell and countless other philosophers and theologians.
So much of fire as would not burn, but gave gentle light, they formed into a substance related to the light of everyday life, and the pure fire which is within us and related to it they made to flow through the eyes in a stream smooth and dense, compressing the whole eye and specially the center part, so that it kept out everything of a coarser nature and allowed to pass only its pure element.

12. Alhazen (Ibn al-Haytham)
End of visual rays
Alhazen (Ibn al-Haytham)
Born
July 1, 965 CE (354 AH) Basra in present-day Iraq, Buyid Persia
Died
March 6, 1040 (aged 74) (430 AH) Cairo, Egypt, Fatimid Caliphate
Fields
physicist and Mathematician
Known for
Book of Optics, Doubts Concerning Ptolemy, On the Configuration of the World, The Model of the Motions, Treatise on Light, Treatise on Place, scientific method, experimental science, experimental physics, experimental psychology, visual perception, analytic geometry, non-Ptolemaic astronomy, celestial mechanics
Influences
Aristotle, Euclid, Ptolemy
Influenced
Averroes, Witelo, Roger Bacon, Kepler
Over-confident about practical application of his mathematical knowledge, he assumed that he could regulate the floods of the Nile.
“There is no vision unless something comes from the visible object to the eye, whether or not anything goes out”
camera obscura

13. Measurements of the Speed of Light

15. By watching the moons circling Jupiter through a telescope, he was able to observe the exact time that the moon moved behind Jupiter. After many years of observations, however, he noticed that the time intervals between eclipses were not always the same.
(position 1): The light from the eclipsing moon sometimes took a relatively short time to reach earth.
(position 2): when earth was in a farther part of its orbit, the light from Jupiter's moon would take longer to reach earth.
Roemer was able to use the time difference and the diameter of Earth's orbit to calculate the speed of light. He determined it to be about 185,000 miles per second, or 296,000 kilometers per second, very close to the actual value.
Ole Rømer
Born
25 Sept. 1644; Århus
Died
19 Sept (aged 65) Copenhagen
Nationality
Danish

16. Light Speed measurement
Hippolyte Fizeau
Born
Sept. 23, 1819 Paris
Died
Sept. 18, 1896 Venteuil
Nationality
French
Fields
Physics
Known for
Doppler Effect Fizeau-Foucault apparatus Capacitor
using a pair of toothed wheels driven by a very fast motor.
As the toothed wheels turned, a beam of light shone through the gaps between the teeth of one wheel would on ly pass through the gaps in the other wheel if they lined up.
Knowing the speed that the wheels were turning allowed him to calculate the speed of light with an accuracy similar to Roemer's.

17. Albert Abraham Michelson
Michelson's method was to shine a light on the rotating hexagonal mirror, which then reflected to the other mirror 35 kilometres away. The mirror needed to make one-eighth of a rotation in the time it took the light to make the return trip. This meant that the octagonal mirror had to be turning at about rpm. From the round trip distance the light travelled, and the period of rotation of the octagonal mirror, the speed of light was determined quite accurately.
Albert Abraham Michelson
Born
December 19, 1852; Strzelno, Kingdom of Prussia
Died
May 9, 1931; Pasadena, California
United States; Physics
Alma mater: United States Naval Academy, University of Berlin; Doctoral advisor: Hermann Helmholtz; Doctoral students: Robert Millikan
Known 
For
Speed of light Michelson-Morley experiment
Notable awards
Nobel Prize for Physics (1907) Copley Medal (1907) Henry Draper Medal (1916)

18. The Search for Aether Michelson - Morley Experiment(1887)
No aether drift was detected, despite repeated experiments!
Conclusion:
jundi Shapur University, Dezful is the center of the Universe or
There is No Aether

19. Measuring Earth’s Movement through the Aether
Rotating the apparatus would give the direction of the aether drift
Showed that there is no such thing as aether (nor any need for it). Light is perfectly happy traveling in a vacuum.
The speed of light is the same in any direction, which explains the null result of Michelson and Morley.

20. Wave Theory – Light travels as a transverse electromagnetic wave

21. Magnet and Magnetism
certain iron oxides were discovered in various parts of the world, notably in Magnesia in Asia Minor, that had the property of attracting small pieces of iron.
Magnesia within Greece

22. discovered that electric currents create magnetic fields.
Hans Christian Ørsted
Born
14 August 1777 Rudkøbing, Denmark
Died
9 March 1851 (aged 73)Copenhagen, Denmark
Nationality
Danish
Fields
physics, chemistry
Known for
electromagnetism
discovered that electric currents create magnetic fields.

23. relates the integrated magnetic field around a closed loop to the electric current passing through the loop.
André-Marie Ampère
Born
20 January 1775 Parish of St. Nizier, Lyon, France
Died
10 June 1836 (aged 61) Marseille, France
Residence
France
Nationality
French
Fields
Physics
Institutions
Bourg-en-Bresse École Polytechnique
Known for
Ampere's Law

24. The induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit.
Michael Faraday
Born
22 September 1791Newington Butts, England
Died
25 August 1867 (aged 75) Hampton Court, Middlesex, England
Residence
England
Nationality
British
Fields
Physics and chemistry
Institutions
Royal Institution
Known for
Faraday's law of induction; Electrochemistry; Faraday effect; Faraday cage; Faraday constant Faraday cup; Faraday's laws of electrolysis;Faraday paradox; Faraday rotator; Faraday-efficiency effect; Faraday wave;Faraday wheel;Lines of force
Influences
Humphry Davy William Thomas Brande
Notable awards
Royal Medal (1835 & 1846) Copley Medal (1832 & 1838) Rumford Medal (1846)

25. Heinrich Rudolf Hertz
Born
February 22, 1857 Hamburg, Germany
Died
January 1, 1894 (aged 36) Bonn, Germany
Fields
Physics; Electronic Engineering
Institutions
University of Kiel University of Karlsruhe University of Bonn
Doctoral advisor
Hermann von Helmholtz
Known for
Electromagnetic radiation Photoelectric effect

27. NATURE OF WAVES
Waves (Def.) – A wave is a disturbance that transfers energy.
Medium – Substance or region through which a wave is transmitted.
Speed of Waves – Depends on the properties of the medium.

28. Transverse Waves Energy is perpendicular to direction of motion
Moving photon creates electric & magnetic field
Light has BOTH Electric & Magnetic fields at right angles!

29. Light consists of a varying electric and magnetic field
So, What is Light?
Light consists of a varying electric and magnetic field

30. Electromagnetic Spectrum
The behavior of EM radiation depends on its wavelength.
Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.
A photon of ultra-violet radiation carries more energy than a photon of infrared radiation.
© 2000 Microsoft Clip Gallery

31. Invisible Spectrum Radio Waves Short Wavelength Microwave
Def. – Longest wavelength & lowest frequency.
Uses – Radio & T.V. broadcasting.
Short Wavelength Microwave
Infrared Rays
Def – Light rays with longer wavelength than red light.
Uses: Cooking, Medicine, T.V. remote controls
© 2000 Microsoft Clip Gallery

32. The shortest wavelengths in the visible spectrum are purple, and the longest wavelengths are red.
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.

36. Electromagnetic Spectrum
Visible Spectrum – Light we can see
Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet.
Largest to Smallest Wavelength.

37. Visible Light
We now know what we see is part of the electromagnetic spectrum. We know that the light waves enter our eye, and stimulate parts of it that cause a electrical impulse to be sent to the brain which creates this visual image.
But everything does not emit radiation. How do we see those things? And why cant we see a window?

38. Only red light is reflected
Seeing colour
The colour an object appears depends on the colours of light it reflects.
For example, a red book only reflects red light:
Homework
White
light
Only red light is reflected

39. A white hat would reflect all seven colours:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light

40. Using coloured light
If we look at a coloured object in coloured light we see something different. For example, consider a football kit:
Shirt looks red
White
light
Shorts look blue

41. In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue

42. Seeing things
We know that when waves run into a boundary they are partially transmitted and partially reflected.
Light behaves as a wave, so it to is reflected.
Therefore, an object does not need to emit photons itself to be seen, it just has to reflect light back to our eyes where we can detect it.
Objects that do not allow light to pass through them are called opaque.
Objects that allow light to pass through them are considered transparent.
Objects in between are called translucent.
© 2003 Mike Maloney

43. Invisible spectrum (cont.).
Ultraviolet rays.
Def. – EM waves with frequencies slightly higher than visible light
Uses: food processing & hospitals to kill germs’ cells
Helps your body use vitamin D.
X-Rays
Def. - EM waves that are shorter than UV rays.
Uses: Medicine – Bones absorb x-rays; soft tissue does not.
Lead absorbs X-rays.

44. Light sources
Thermal: a body at a given temperature emits a characteristic spectrum of black-body radiation. As the temperature increases, the peak shifts to shorter wavelengths, producing first a red glow, then a white one, and finally a blue colour as the peak moves out of the visible part of the spectrum and into the ultraviolet.

45. Atoms: emit and absorb light at characteristic energies
Atoms: emit and absorb light at characteristic energies. This produces "emission lines" in the spectrum of each atom.
Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames (light from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow light).
Emission can also be stimulated, as in a laser or a microwave maser.

46. Deceleration of a free charged particle, such as an electron, can produce visible radiation: cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this. Particles moving through a medium faster than the speed of light in that medium can produce visible Cherenkov radiation.

47. Certain chemicals produce visible radiation by chemoluminescence.
In living things, this process is called bioluminescence.
For example, fireflies produce light by this means, and boats moving through water can disturb plankton which produce a glowing wake.
Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence.
Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence.
Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is used in cathode ray tube television sets and computer monitors.

48. Certain other mechanisms can produce light:
Scintillation; electroluminescence; sonoluminescence; triboluminescence; Cherenkov radiation; Bioluminescence.
When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include: Radioactive decay; Particle–antiparticle annihilation

49. Kinds of Spectra

50. Polarization
Polarization is a phenomenon of light that is used in sun-glasses and 3-D movies.
Play with the two polarizing filters for a few minutes and note what is happening and see if you can think of any reasons for it.
© 2003 Mike Maloney

51. Polarization Hint Light vibrates in all directions.
A polarizing filter acts like a picket fence. It only lets certain direction vibrations pass through it.
Therefore, if you pass light through two of them you can completely block the light from passing through.
HOW?
© 2003 Mike Maloney

52. Polarization http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=692.0
© 2003 Mike Maloney

53. Light Energy
When EM radiation interacts with single atoms and molecules, its behaviour depends on the amount of energy per quantum it carries.
Atoms
As atoms absorb energy, electrons jump out to a higher energy level.
Electrons release light when falling down to the lower energy level.
Photons - bundles/packets of energy released when the electrons fall.
Light: Stream of Photons

54. Quantum Theory – Light consists of small particles (photons)
Newton’s Corpuscular Theory of Light - light consists of small particles, because it:
• travels in straight lines at great speeds
• is reflected from mirrors in a predictable way
Position x
Momentum p = mv

55. Why the Photon is Necessary
Electron transitions in the Bohr model of the atom and the subsequent emission of light provides an example of when light should be viewed as a photon. There are two further pieces of evidence of this particle-like nature of light:
• photon scattering
• photoelectric effect

56. Scattering
One experiment which provides conclusive proof of a particle nature of objects is to scatter two objects off of each other, as in the collision of two billiard balls. This experiment with light and small atoms has been done, and is called Compton scattering.
The results of this experiment are completely at odds with predictions made if light is viewed only as a wave. Measurements show that the frequency of the scattered wave is changed, which does not come out of a wave picture of light. However, when the light is viewed as a photon with energy proportional to the associated light wave, excellent agreement with experiment is found.

57. Photoelectric Effect
Another compelling proof for the photon nature of light is the photoelectric effect. In this effect, light is shone at a metal plate and it is found that electrons are ejected. These electrons then get accelerated to a nearby plate by an external potential difference, and a photoelectric current is established.
This effect, which arises in devices such as automatic door openers, burglar alarms, light detectors, and photocopiers, cannot be explained using a wave picture of light.

58. Einstein’s Photoelectric Effect
Only light with a frequency greater than a certain threshold will produce a current
Current begins almost instantaneously, even for light of very low intensity
Current is proportional to the intensity of the incident light

59. Planck’s Quantum Postulate
Energy of radiation can only be emitted in discrete packets or quanta, i.e., in multiples of the minimum energy E = hf
where h is a new fundamental
constant of nature: h = 6.63 x Joules sec

60. We Believe in Photons
Red light is used in photographic darkrooms because it is not energetic enough to break the halogen-silver bond in black and white films
Ultraviolet light causes sunburn but visible light does not because UV photons are more energetic
Our eyes detect color because photons of different energies trigger different chemical reactions in retina cells

61. Special Relativity: Postulates
Principle of Relativity
All the laws of physics are the same in all inertial reference frames, i.e. frames moving at constant velocities w/respect to each other.
Constant Speed of Light
The speed of light, c = 3×108 m/s, is equal in all inertial frames, regardless of the velocity of the observer or the light source.
Consequences of Special relativity
“Slowing” down of clocks (time dilation) and length contraction in moving reference frames as measured by an observer in another reference frame.

62. Galilean Transform: Predicts Preferred Ref. Frame
According to the Galilean transform, the travel time t1 across & back a river is shorter than the travel time t2 up & down a river.
Light moving in an “ether” is an analogous problem.
Can light have different travel times? t1 t2
Phys Baski
Relativity I

63. Galilean Transform: NO Preferred Ref. Frame for Light!
In 1800’s, scientists thought that light propagated through some type of “ether.”
Michelson-Morley Experiment (1887)
Test if ether exists and sets “preferred” reference frame.
Analogous to rowboat in river.
Measure light speed relative to earth’s motion (// and ) using an interferometer (fringes).
Result: No detection of “ether”
No detectable shift in interference fringes occurred, indicating that light speed DID NOT depend on direction.
Phys Baski
Relativity I

64. Doppler Shift Doppler shift causes change in measured frequency.
When a light source moves towards an observer, the light frequency is shifted higher (i.e. blue shift).
When a light source moves away from an observer, the light frequency is shifted lower (i.e. red shift).
Only difference with “classical” Doppler shift for sound is the incorporation of time dilation (causes square root factor).
Approaching - blue shift
Note: For a receding source, switch signs.
Phys Baski
Relativity I

65. Cool Thing About Light
It can be thought of as both a particle and a wave, so called “particle-wave duality”
Lower energy (longer wavelength) light acts predominately like a wave
High energy (shorter wavelength) light acts predominately like a particle

66. Cool Things Light Can Tell Us
It can tell us what you are made out of
It can tell us if you are moving toward or away from us
It can tell us how far away you are or (if we already know that) how energetic you are
It can tell us your temperature

67. Another Way to Look at a Spectrum

68. Spectral Lines
Lines from excited sodium gas in the laboratory