PHY 102

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PHY 102 Atoms to Galaxies
PHY 102 Atoms to Galaxies
Our early human ancestors most certainly looked
at the night sky, and wondered.
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Chapter 8 Light
Electromagnetism

• Waves

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• Wave
• Not a material object, but a moving pattern
  bumps on the surface of water, deformations of
  music strings, variations in air pressure,
  oscillations of electromagnetic fields, etc.

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Two types of waves

• 1. Transversal Waves with propagating
  direction perpendicular to the oscillation
  direction.
• 2. Longitudinal Waves with propagating
  direction parallel to the oscillation
  direction.

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Two principles

• 1. Speed Waves move at a constant speed that
  is determined by the medium where they travel,
  rather than the waves themselves.
• 2. Superposition If two or more waves arrive
  simultaneously at the same place, the resulting
  effect is simply the sum of the effects of the
  waves.

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Speed of soundin various media
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Moving bumps and periodic waves
(http//members.aol.com/nicholashl/waves/waves.htm
)

• wavelength l (m) length of the wave
• frequency f (/s) number of oscillations over
  time
• faudible 20 to 20,000 Hz (humans)
• faudible lt 20 Hz
• faudible gt 20,000 Hz

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• wavelength l (m)
• frequency f (1/s)
• faudible 20 to 20000 Hz
• wave speed v l f
• vsound 340 m/s
• vlight 300 000 000 m/s
• 300 000 km/s
• 186 450 mi/s

• If Earth-Sun distance is 92 million miles
• (150 million km), how long for the light from
  the Sun to reach the Earth?

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17th century physics planets
Many 17th century scientists did not believe in
speed of light. Galileo 1670's, the
Danish astronomer Ole Roemer discovered that Io
didn't always appear where it was supposed to
be. c 300 000 km/s 1888, H. Hertz
generated EM waves in his lab.
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Christian Huyghens

• In 1673 reported synchronization between two
  pendulum clocks hanging on the same wall.

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• Superposition If two or more waves arrive
  simultaneously at the same place, the resulting
  effect is simply the sum of the effects of the
  waves.
• Interference Result of different waves traveling
  through the same medium interacting with one
  another.

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Interference

• When periodic waves arrive at the same place from
  two synchronized sources, or from the same source
  but traversing two different paths, they produce
  an interference pattern.

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Interference
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Difraction

• Process by which waves spread out as a result of
  passing a narrow aperture, or across an edge,
  typically accompanied by interference between the
  wave forms produced beyond the aperture or edge.

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Difraction Thomas Young, 1803.
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Light Particle or Wave?

• From the mid-1660s on Newton conducted a
  series of experiments on the composition of
  light, and established the modern study of
  optics. He adopted the corpuscular theory of
  light according to which light is made of tiny
  particles emitted in all directions by a source.
• The theory explained well reflection a
  reflecting force would push the light particles
  away from the surface.

• Reflection

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Light Particle or Wave?

• Newton discovered that white light is composed of
  the same system of colors that can be seen in the
  rainbow.

• Refraction

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Light Particle or Wave?

• Newtons corpuscular theory of light had a
  few difficulties, such as explaining refraction.

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Light Particle or Wave?

• From the diffraction experiment with light
  there is good evidence that light is a wave.

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Light
George McCoy
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So the concept of light as a wave goes beyond the
visible spectrum.

• Question If light is a wave, what medium is
  light
• traveling through on its way from
  the
• Sun to Earth?
• This and other questions were being asked in
  the 1800s. The answer is intrinsically related
  to electricity and magnetism.

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Light as a wave

• Light is an electromagnetic wave
• traveling through an
• electromagnetic field.

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Electricity

• Form of energy resulting from the existence
  of charged particles, such as electrons or
  proton.
• (Thesaurus Dictionary)
• From experiments we know that the charge of the
  proton (e) exactly equals the charge of the
  electron (-e), where e 1.6 x 10-19 coulomb.

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Electricity

• Law of conservation of electric charge During
  any process, the net electric charge of an
  isolated system remains constant (is conserved).
• Fundamental characteristic of electric charges
• Like charges repel and
• unlike charges attract each
  other.

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Electricity

• Coulombs Law
• The magnitude of the electrostatic force exerted
  by one point charge q1 on another point charge q2
  is directly proportional to the magnitude of the
  charges and inversely proportional to the square
  of the distance r between them
• F k q1
  q2 / r 2
• where k 9 x 109 N m2/C2.

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Magnetism

• Two nearby bar magnets either attract or repel
  each other.
• The ends of a bar magnet are called north and
  south magnetic poles.
• Each bar magnet has two poles. Monopoles are
  yet to be found.

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Magnetism

• Fundamental characteristic of magnetic poles
• Like poles repel and
• unlike poles attract each
  other.
• This attraction (or repelling) force is a new
  type called magnetic force.

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Magnetism

• Experiments show that electrically charged
  objects that are moving exert and feel an
  additional force beyond the electric force that
  exists when they are at rest. This additional
  force is the magnetic force.
• All magnetic forces are caused by charges in
  motion.

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The Electric Atom

• The planetary model of the atom depicts the atom
  as almost entirely empty, divisible and made of
  many parts.
• Nucleus (constituted of neutrons and positively
  charged protons) surrounded by tiny negatively
  charged electrons.

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The Electric Atom

• Order of magnitude the overall size of an atom
  is about 10-10 m.
• The nucleus is about 10,000 times smaller than
  the atom.

A scaled-up model of the atom with a nucleus the
size of a soccer ball would have the electrons as
dust specks several kilometers away.
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The Electric Atom

• Order of magnitude the overall size of an atom
  is about 10-10 m.
• The nucleus is about 10,000 times smaller than
  the atom.

A scaled-up model of the atom with a nucleus the
size of a soccer ball would have the electrons as
dust specks several kilometers away.
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Faradays Law

• When a wire loop is placed in the vicinity of a
  magnet and when the loop or the magnet is moved,
  an electric current is created within the loop
  for a long as the motion continues,
• or,
• A changing magnetic field creates an electric
  field.

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The principle of electric power generation
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Chapter 9
Electromagnetic Radiation
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Electromagnetic radiation

• James C. Maxwell, Scottish, in the 1860s
  developed a theory that unified electricity and
  magnetism.

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Electromagnetic radiation

• Every vibrating charged object creates a
  disturbance (wave) in its own electromagnetic
  field. This disturbance spreads outward through
  the field at light-speed, 300,000 km/s . Light is
  just such an electromagnetic wave.

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Electromagnetic radiation

• Heinrich Hertz, German, in the 1890s
  demonstrated experimentally that electromagnetic
  waves can travel in space and induce oscillations
  at a distance from where they were generated.

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Electromagnetic radiation

• Guglielmo Marconi, Italian, in the late 1890s
  developed wireless telegraphy which became the
  basis for the radio and television revolution.

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Ether

• The Newtonian clockwork model had no room for new
  phenomena like light traveling in empty space
  ? ether ? Hypothetical medium for transmitting
  light and heat (radiation), filling all
  unoccupied space.

• all attempts to demonstrate its existence, most
  notably the Michelson-Morley experiment of 1887,
  produced negative results

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Field

• Field a region of space characterized by a
  physical property, such as gravitational or
  electromagnetic force or fluid pressure, having a
  determinable value at every point in the region.

• The special theory of relativity, proposed by
  Albert Einstein in 1905 eliminated the need for a
  light-transmitting medium.

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Solar Radiation and Earth
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Solar Radiation and Earth
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Solar Radiation and Earth
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Ozone Depletion

• Ozone depletion
• 1928, GMC, inert chlorofluorocarbons (CFCs)
• Where are CFCs going? Crutzen, Molina, Rowland
  (1974)
• u-v radiaton ? Chlorine (Cl)
• Cl O3 ? ClO O2
• ClO ClO sunlight ? Cl Cl O2
• A single Cl atom destroys about 100,000 ozone
  molecules!

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Ozone Depletion Susan Solomon, 1986
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Global Warming

• Hypothetical Earth with normal atmosphere except
  for no greenhouse gases.

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Global Warming

• Realistic Earth with normal atmosphere including
  trace amounts of greenhouse gases.

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Global Warming
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Global Warming

• Atmospheric concentration of carbon dioxide
  between 1000 and 2003.

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Global Warming
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Global Warming
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Global Warming

• Carbon dioxide concentration
• and
• temperature

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Global Warming
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Global Warming Consequences

• Climate zones shift about 500 km away from
  Equator
• 1.25 million species extinction by 2050
• Accelerate Greenland and Antarctic ice melting
• Increase rate of sea level rise
• Mixed agricultural effects
• Thrive of mosquitoes and other disease vectors
• Northward spread of tropical diseases (malaria,
  dengue)

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Global Warming What to do?

• 1997, Kyoto Industrialized nations agreed to
  reduce their greenhouse gases emission 5 below
  1990 levels by the year 2012.
• As of 2001, emissions were 10 above 1990 levels
• Actually, 60-80 reduction is needed
• The U.S. with 4.5 of worlds population emits
  23 of worlds carbon, did not sign the Kyoto
  Protocol.

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Global Warming Precautionary Principle

• Scientific uncertainty should not be a reason to
  postpone measures to prevent harm.

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Chapter 10 Special Theory
of Relativity

• In the late 1800s it was believed that the era of
  new discoveries in fundamental physics was likely
  ended. The future would be to improve the
  accuracy of known results. But

In 1900 the German physicist Max Planck
introduced a revolutionary idea, the quantum of
energy. The new idea was hardly noticed,
initially.
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Special Theory of Relativity

• In 1905 a different but also revolutionary idea
  was introduced by a patent clerk in Switzerland,
  Albert Einstein.

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Galilean Relativity

• Relative motion
• Reference frame
• vball/train 20 m/s
• vtrain/ground 70 m/s
• vball/ground ?

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Galilean Relativity

• Relative motion
• Reference frame
• c 300,000 km/s
• vlight/ship c
• vship/ground 0.25 c
• vlight/ground ?

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The Principle of Relativity

• Every non-accelerated observer observes the same
  laws of nature,
• or
• No experiment performed within a sealed room
  moving at an unchanging velocity can tell you
  whether you are standing still or moving.

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The Principle of the Constancy of
Lightspeed

• The sped of light (any electromagnetic radiation)
  in empty space is the same for all nonaccelerated
  observers, regardless of the motion of the light
  source or the observer.
• 1964, fast subatomic irradiating particle
• experimental evidence.

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Michelson-Morley experiment, 1887, ether
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Time is relative

• If the speed (distance over time) of light is
  constant, then perhaps we need to revisit the
  concepts of distance and time.
• Lets measure time with a light clock from two
  distinct reference frames.

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Mort and Velma use identical clocks and measure
different time intervals for the same event the
relativity of time.
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Mort and Velma use identical clocks and measure
different time intervals for the same event the
relativity of time.

• tM time interval measured by Mort
• tM time interval measured by Velma
• v speed of ship (relative speed)
• c lightspeed

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Duration of one clock tick (1 second in the
clocks reference frame) on a clock
moving relative to the reference frame.

• Muon s lifetime has been shown to be different
  depending on their speed.
• Fast muons live longer.

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Time Travel Back to the Future?

• Velma (assumed same age as Mort) travels away at
  0.75c relative to Mort and comes back after 60
  years on Morts clock. How old will she be upon
  her return?

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Relativity of Space and Mass

• Time and space are tangled up with each other.
• Length contraction
• Space is different for different observers.

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Mort and Velma use identical meter sticks and
measure different lengths for the same object
the relativity of space.

• LM lenght measured by Mort
• LM length measured by Velma
• v speed of ship (relative speed)
• c lightspeed

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