New Technologies in the inspirational Physics Teaching

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New Technologies in the inspirational Physics
Teaching

• J.D. Vergados
• University of Ioannina, Greece

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I hope that you agree that

• Delivering technically good lectures and
  executing accurate physics experiments is a
  necessary, but not sufficient condition

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I hope that you agree that

• Delivering technically good lectures and
  executing accurate physics experiments is a
  necessary, but not sufficient condition
• A good teacher must excite the minds of the young
  to motivate them to pursue knowledge, especially
  in the hard and not economically rewarding
  disciplines.

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I hope that you agree that

• Delivering technically good lectures and
  executing accurate physics experiments is a
  necessary, but not sufficient condition
• A good teacher must excite the minds of the young
  to motivate them to pursue knowledge, especially
  in hard and not economically rewarding
  disciplines.
• Inspirational teaching has to fight against the
  odds of the short term goals imposed, e.g., by
  the University Entrance Exam.

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New technologies can

• Aid in delivering technically and pedagogically
  fine lectures
• Aid an inspired teacher in preparing and
  presenting exciting material
• I will concentrate here on the second aspect
  drawing from my long experience as a University
  Teacher and benefiting from my contact with high
  school teachers

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Broaden Horizons of Science

• Expand to other sciences
• e.g. Cosmology and Biology (physics is
  invaluable in biology. It provides concepts,
  instruments, modeling)
• Explain exciting events of everyday life (a
  specific illustration will be the perception of
  color)
• Exhibit the broad applicability of the basic
  physics concepts Length, energy etc
• (specific illustration will be the measurement
  of length)
• Exploit current experimental facilities to study
  ordinary problems, e.g. learning magnetism from
  LHC (CERN)

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PART A

• THE PERCEPTION OF COLOR

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Color perception is not just radiation of a given
wavelength!
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The three colors (r, g, b) when combined yield a
variety of colors
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The mechanism of vision

• Cones responsible for color and detail
• Rods responsible for seeing in dim light and
  spotting movement

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Color sensors Cones.There exist three types of
cones
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The three basic colors (r, g, b) ?white
?Additive colors (screens)

• Scanners
• screens
• emit light
• They mix
• light
• Additive
• process

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Subtractive basic colors YMC-K (cyan, magenta,
yellow)?black? printers

• Printers are
• covered with
• colored
• substance.
• For viewing they
• reflect light
• Subtractive
• process

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The 1976 CIE Chromaticity Diagram (see Zaharis,
Thesis, UOI)

• RGE cannot
• reproduce
• all colors seen
• by the eye
• Only those
• Inside
• The triangle

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PART B

• MEASUREMENT OF LENGTH
• FROM ORDINARY TO LARGE SCALES
• The equally exciting small scale is not going to
  be discussed here.

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Measurement of Length I Body Length Units the
measuring stick
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Standard meter (CGPM, 1889)

• Conférence Générale des Poids et Mesures (CGPM)
  established the International Prototype Metre as
  the distance between two lines on a standard bar
  of an alloy of ninety percent platinum and ten
  percent iridium, measured at the melting point of
  ice.

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Standard meter (CGPM, 1960)

• The standard meter is defined as equal to
  1,650,763.73 wavelengths in vacuum of the
  radiation corresponding to the transition between
  the 2p10 and 5d5 quantum levels of the
  krypton-86 (86Kr) atom.

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Standard meter (CGPM, 1960)

• The seventeenth CGPM defines the length to be the
  distance travelled by light in vacuum during a
  time interval of 1/299 792 458 of a second.
• The speed of light is set exactly at
  299792458
• International System, the 13th CGPM (1967)
  decided to replace the definition of the second
  by the following (affirmed by the CIPM in 1997
  that this definition refers to a cesium atom in
  its ground state at a temperature of 0 K)
• The second is the duration of 9 192 631 770
  periods of the radiation corresponding to the
  transition between the two hyperfine levels of
  the ground state of the cesium 133 atom.

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Measurement of Length II Similar
shapes-proportions

• ORDINARY DISTANCES
• The Measurement of unreachable objects, e.g. the
  width of a river, the height of pyramids etc.
• Estimation of distance by the eye
• (air-line type measurement).
• Triangulation ?Knowledge of one side and two
  angles of a triangle determines the triangle
  completely.

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Measurement of height Use of the shade of a
known object
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What is the width of a River (AX)? Choose some
length AB. Choose a BC, e.g. BC(AB)/2, and D so
that DBXstraight line ? (AX)2 (CD)
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Measurement of Length IIb Triangulation
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Measure angle B (520) and distance AB450m?AT675
meters
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Back in biology.Measurement of Length IIc
(inside the body). What is the distance between
the cones of the fovea?

• Attach on a wall a sheet of paper with a set of
  parallel lines separated by a distance D3mm
• Ask a student to approach the sheet so that the
  lines a barely resolved. Let the students
  distance from the sheet be L10m
• Assume that the distance from the iris (front of
  the eye) to the retina is l15cm

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Here is the geometry D3mm, l15mm, L10m, d?

• d/15mm1mm/10m ? d1.5x10-6m 1.5 µm (diameter
  of a cone)

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The eye vs a digital camera.Cone diameter d1.5µm

• The area of the fovea is 1mm2 ?
• The number of cones (pixels) is 500000
• Typical good digital camera 5x106pixels!
• Yet, the eye has a better view of a pretty
  landscape. How come?
• The eye can at will change the point it focuses
  on!

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How does the eye estimate the distance of a car
in the highway?

• Do it! Simple geometrical optics

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Measurement of Length III The Earths radius
(Eratosthenes, 276-194 AD)

• Radius R(360/?)( (??)/2p)
• (AB)distance between
• Syene (B) and Alexandria (A)
• 5000 stadiums800 km
• ??A- ?B 7.2 deg
• ?Bangle of the sun rays
• from zenith in Syene (zero
• that day)
• ?A angle of the sun rays
• from zenith in
• Alexandria
• ?
• R6366 km
• Present value
• R6378 km

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Measurement of Length IV The parallax Method.

• Fact Close objects move (relative to distant
  ones) as the observer moves.
• Essential quantities
• a) A known long baseline. Typically
• -The diameter of the earth
• -The diameter of the ecliptic
• b) the angle the baseline is seen from a distant
  object

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The notion of parallax Put a finger in front of
your nose. Look at it with one eye closed. Then
with the other
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The notion of parallax Put a finger in front of
your nose. Look at it with one eye closed. Then
with the other
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Parallax Application Close objects move
(relative to distant ones) as the observer moves!
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Animated Parallax (exaggerated)
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On paper everything fine, but.
d(1AU)/p?d3.262/(p/1) ly

• 1AU149597900km p0.762 (a-century)

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Still Larger Distances

• Triangulation cannot be applied for distances
  greater than 500 ly
• (1 ly0.946x1016 m6.324x104 AU)
• We need a new idea
• Standard candles
• a) Cepheid variable stars up to 50x106 ly
• b) Supernovae Ia up to 1x109 ly 1/10 of
  the radius of the universe (so far!)

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Identical stars may show different brightness
(relative luminosity)
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The Luminosity falls as 1/r2
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Prototype Cosmic Candles

• L Absolute Luminosity (emitted power)
• ? Relative Luminosity
• (Power per unit area of detector)
• That is Knowledge of L and Measurement of ?
• Determine the optical
  depth" D
• L depends on the physics governing the emitting
  source.

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Prototype A Cepheids Variable stars. Absolute
luminosity is related to their period.
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The cycle of a large mass star SourceImagine the
Universe, NASA
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Supernovae Ia All have the same mass (1.4
msolar)? All have the same (absolute) luminosity

• They are very bright
• They are easily detectable (but very rare, one
  every 500 years in our galaxy)
• They can be identified from their spectrum and
  light curve

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Supernova I A white Dwarf is eating up the mass
of a red giant. It explodes when its mass becomes
1.4 msolar
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Light curve of supernovae Ia
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Bonus Once one can see so deep, one can get the
deepest picture of the sky as it looked 12
billion years ago!
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Concluding remarks from the chosen experiment
on Length

• It may be interesting to look at any fundamental
  observable (Length, time, mass, energy, momentum,
  angular momentum etc) from a broader perspective,
  while making the presentation technically as easy
  as possible.
• This approach requires a different operational
  definition of the chosen observable at each
  level. A new idea leading to a different
  apparatus is usually needed.
• The successive levels must have a common range to
  allow for the needed calibration.

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Concluding remarks

• The new technology
• Allows the teacher to easier follow the recent
  developments in the field.
• Allows for an easy accumulation of the needed
  information.
• Allows a technically superior presentation of the
  ideas
• It cannot, however, tell anyone what the
  interesting material is

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This experiment is fine, but..

• Will the physics teachers appreciate this
  approach?
• Will they merely view it as an obstacle in their
  efforts towards covering the material?
• Given their pupil body, will they be able execute
  such a program properly to motivate them to
  overcome their frustration with having to do the
  tedious day-to-day work?
• Will some pupils/students find this approach
  interesting?
• Will any pupils/students find this approach
  useful? Or
• will the pupils/students find this approach
  derailing them from their basic goals? Do not
  forget the grade hunting and the Minotaur
  University Entrance Examination.

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• THAT IS THE QUESTION!

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• THE END

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Stellar Parallax
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