OPTICS, WAVES AND ELECTROMAGNETIC RADIATION

• Ancient Philosophy and Light– Laws of Reflection and Refraction– Theories of Vision

• Rome and Decline of Natural Philosophy• Arab Natural Philosophy and its Rebirth in the West• Light: Particle or Wave

– Types of Waves– Interference and Resonance

• Discovery of the EM Spectrum• Demise of the Ether

Time line of Ancient Philosophy as it relates to the origins of science

Reflection and Refraction

Both properties of light obey rectilinear, geometric laws

Lenses and Refraction

Biconcave lens

Biconvex lens

Emission & Intromission Theories of Vision

Emission• Vision is sensation from rays

emitted by the eye• Multiple points• Thus, vision is external to

the eye• Earliest Proponents:

– Pythagoras?– Plato– Euclid– Ptolemy

Intromission• Vision is from physical forms

entering the eye• Single object• Vision occurs within the eye• Earliest Proponents:

– Aristotle– Galen

Arabic Natural Philosophy

Abu Ali al-Hasan ibn al-Hasan ibn al-Haythamالهي بن الحسن بن الحسن علي، أبو

Alhazen, the Persian

• Modified intromission theory to support multiple rays of Euclid and Ptolemy, but from the object

• Used geometrical, optical, and anatomical arguments

• Wrote 7-volume treatise on Optics based on his observations and experimental work

• Proposed speed of light was finite

965 (Basra in present-day Iraq) – 1040 Cairo, Egypt

Rebirth of Philosophy in Western Europe

• The fall of Islamic Empire in Spain• Capture of Toledo and its library (1085)• Translations of Greek texts from Arabic to Hebrew

to Latin –much guided by Albertus Magnus (1193/1206-1280; present-day Germany)

• Greek philosophy, especially Aristotle, accommodated to church doctrine by Thomas Aquinas (1225-1274; present-day Italy). Natural philosopher with concept of Deux Veritas; intromission vision theory adopted

In the transition, there was a discussion about the relationship between material theories of light and vision.

Kepler, vision, and light• Johannes Kepler (1571-1630), in the mathematical

tradition of medieval perspectivists, and benefiting from the ocular anatomy presented by Felix Platter (1536-1614).

• 'How an infinity of rays from each point in the visual field is drawn into a coherent, point-to-point correspondence in the eye.' Against tradition, Kepler argued that the crystalline lens re-focused intromitted rays on the retina where vision was made possible. Significantly, Kepler called this image a 'pictura.'

• However, as Alhazan had shown, such a lens makes an upside-down picture.

Rene Descartes (1596-1650)

• In his need to connect the observer with the observed (Cartesian dualism)– Tied the world we see with the mechanical body

by means of tiny threads (not as pictures)– Interpret visual information by linguistic theory

(we have an innate ability to interpret visual information)

Francesco Maria Grimaldi

Noted diffraction of light (a term coined by Leonardo da Vinci), cannot be explained if light operates only by rectilinear laws.

1618-1663, present-day Italy

Optics of Isaac Newton• Light is corpuscular and

obeys rectilinear laws• Newton proposed that light

corpuscles propagate in a luminous ether

• Light comes from a luminous source and reflects off of visible objects

• White light is made of all colors

Christiaan Huygens

• Light is a wave• Light has a finite speed• Defined light phenomena

on the basis of wave fronts in the luminous ether

• Invented projector• Invented pendulum clock• Many other contributions

in physics and astronomy 1629-1695, The Dutch Republic

Thomas Young and wave theory of light

• Physician• Interpreter of Rosetta

Stone• Contributed to

theories of vision, mechanics, energy, music, language, physiology

• Interference experiments with light

1773-1829; Great Britain

Observation of Grimaldi best explained if light is a wave

Types of Waves

Transverse wave

Longitudinal wave

Constructive and destructive interference

Constructive Destructive

Resonance

One-slit Experiment

Double-slit Experiment and Interference

Discovery of the EM Spectrum• Visible light: ROYGBV

• 1800 (William Herschel) IR radiation detected by measuring temp of light split by prism; invisible light below red was warm

• 1801 (John Ritter) calorific rays (UV) beyond violet caused photochemical reactions similar to those of violet

• 1845 (Michael Faraday) polarized light altered by magnetic field; thus, light phenomena are electrical and magnetic

• 1860-1870 (James Maxwell) set of equations that suggested a constant velocity of light and described wave patterns in a field

• 1886 (Heinrich Hertz) used Maxwell’s equations to define undiscovered waves (now called radio waves and microwaves). He was able to focus and reflect these waves

• 1895 (Wilhelm Röntgen) defined x-rays• 1900 (Paul Villard), 1910 (William Henry Bragg) gamma radiation

C= Wavelength(meters)*Frequency (Hz)C= 300,000 km/sec

Radio

Gugliemo Marconi1874-1937, Italy

Alexander Stepanovich Popov1859-1906, Russia

Michelson-Morley Experiment (1887)

Albert Abraham Michelson1852-1931, Prussia (now Poland) and USA1st American to win Nobel (1907)

Edward Willliams Morley1838-1923, USA

Doppler Effect

Christian Andreas Doppler1803-1853, Austria

• Suggested color relative to velocity (to explain color differences in binary stars)

• Concept applied also to sound