Transcript WAVES AND ELECTROMAGNETIC RADIATION

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
Biconvex lens
Biconcave 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:
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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-Haytham
‫ الحسن بن الحسن بن الهي‬،‫أبو علي‬
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
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Visible light: ROYGBV
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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
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C= Wavelength(meters)*Frequency (Hz)
C= 300,000 km/sec
Radio
Gugliemo Marconi
1874-1937, Italy
Alexander Stepanovich Popov
1859-1906, Russia
Michelson-Morley Experiment (1887)
Albert Abraham Michelson
1852-1931, Prussia (now
Poland) and USA
1st American to win Nobel
(1907)
Edward Willliams Morley
1838-1923, USA
Doppler Effect
• Suggested color relative to
velocity (to explain color
differences in binary stars)
• Concept applied also to
sound
Christian Andreas Doppler
1803-1853, Austria