Classroom notes for: Radiation and Life

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Classroom notes forRadiation and Life

• 98.101.201
• Professor Thomas M. Regan
• Pinanski 207 ext 3283

2
Class 3 Units and Measures

• Derived Quantities
• Oftentimes when numerically evaluating our
  observations to explain the natural world, it is
  necessary to perform mathematical operations on
  quantities to properly express their
  relationships.
• Derived quantities result when mathematical
  operations have been performed on the fundamental
  (or other derived) quantities.

3
Energy

• Energy is measured in Nm in SI units or
  equivalently, it can be expressed in terms of the
  joule (J), also a shorthand notation.
• Energy comes in many forms light, heat, the
  kinetic energy of a moving object (kinetic
  energy), etc
• To put this unit of measure in perspective,
  consider another unit known as the calorie, which
  used in dietetics for stating the energy (heat)
  content of a food, i.e., the amount of heat
  energy that the food can yield as it passes
  through the body. One calorie 4,185 joules in
  this context.
• The heat of fusion for water is approximately 333
  joules/gram. (http//www.infoplease.com/ce5/CE0086
  11.html)
• The unit is named for the English physicist James
  Prescott Joule (1818-1889).
• (http//www.encarta.msn.com)

4
Power

• Power is measured in J/s in SI units, or in watts
  (W).
• As an example, note that a 100-watt light bulb
  emanates 100 joules of infrared and light energy
  each second.
• The unit is named for the Scottish engineer and
  inventor James Watt (1736-1819).
• (http//www.encarta.msn.com)

5
Flashlight Spectral Emission 4600 K
Wien's displacement law Stefan-Boltzmann law
6
Frequency

• Frequency is measured in cycles per second (1/s),
  also known as the hertz (Hz).
• A cycle can be a toss of the pen from my hand to
  the height of its travel and back it can be a
  wave of water or sound, etc..
• When watching water waves in a pond, the number
  of wave crests that pass by each second is the
  frequency in Hz.
• This unit is named in honor of Heinrich Hertz
  (1857-1894), a German physicist.
  (http//www.encarta.msn.com)

7
Unit Prefixes

• If a quantity is very large, sometimes it easier
  to express it in shorthand notation. For
  example, suppose you measure a distance of 1000
  meters. What is this called?
• In radiation sciences unit prefixes are important
  because the numbers involved tend to be either
  very large or extraordinarily small.
• Some common prefixes in the SI system are
• Numbers larger than one
• prefix multiple abbrev.
• kilo (x1,000) k
• mega (x1,000,000) M
• giga (x1,000,000,000) G
• tera (x1,000,000,000,000) T
• peta (x1,000,000,000,000,000) P
• exa (x1018) E

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To understand the relative scales of these
values, consider

• one kilogram 1,000 grams (weighs about 2.205
  lb on the earths surface)
• one megawatt of electricity would light 10,000
  100-Watt light bulbs
• ½ gigameter is about the distance between the
  earth and the moon (3.84 x108 m).
• Numbers smaller than one (fractions)
• prefix multiple abbrev.
• centi (1/100) c
• milli (1/1,000) m
• micro (1/1,000,000) m
• nano (1/1,000,000,000) n
• pico (one trillionth) p
• femto 10-15

9
Scientific Notation

• Scientific notation is simply another shorthand
  method for writing very large or very small
  numbers.
• Numbers larger than one
• 1 100
• 10 101
• 100 102
• 1,000 103 (kilo)
• 1,000,000 106 (mega)
• 1,000,000,000 109 (giga)
• 1,000,000,000,000 1012 (tera)
• The superscript is called an exponent. For
  numbers larger than one, the number is written as
  a one followed by a number of zeroes equal to
  the exponent.

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• Numbers smaller than one
• 1 100
• 1/10 10-1
• 1/100 10-2
• 1/1,000 10-3
• 1/1,000,000 10-6
• 1/1,000,000,000 10-9
• 1/1,000,000,000,000 10-12
• 1/1,000,000,000,000,000 10-15
• For numbers smaller than one (fractions), the
  number is written as a one divided by a one
  followed by a number of zeroes equal to the
  exponent. Notice that the exponent is negative
  for fractions of one.

11
Historical Developments in Modern Physics

• To understand a science it is necessary to know
  its history. August Comte (1798-1857), the
  French positivist philosopher, was a founder of
  sociology. (http//www.encarta.msn.com)
• Circa 1800, we had a general understanding of the
  world around us.
• Newtons three Laws of Motion were known.
• An object at rest tends to stay at rest, an
  object in motion tends to stay in motion.
• An object continues in its initial state of rest
  or motion with uniform velocity unless it is
  acted on by an unbalanced, or net external,
  force. (Physics 3rd Ed., Tipler, p. 77)
• This may seem to be a counterintuitive thought.
  For example, push a book so that it slides freely
  along the surface of a table, and the book will
  eventually come to a stop. However, this is
  because of friction. If a book were thrown in
  the vacuum of space, it would continue to travel
  forever until it hit something.

12
F ma

• F is force in Newtons,
• m is mass in kilograms, and
• a is acceleration in m/s2.
• Note that F and a are vector quantities.
• With this formula, it is demonstrated that
  exerting a net force on an object will accelerate
  it (speed it up or slow it down). Consider the
  example of throwing the book in a vacuum. Give
  it a single push and it will fly through the void
  at a constant speed. However, push it
  continuously and it will speed up. The book
  sliding on the desk cant continue to move at a
  constant speed because the force of friction is
  causing it to slow down.
• For every action, there is an equal and opposite
  reaction. Forces always occur in pairs. If
  object A exerts a force on object B, an equal but
  opposite force is exerted by object B on object
  A. (Physics 3rd Ed., Tipler, p. 78)

13
Newton Continued

• For every action, there is an equal and opposite
  reaction. Forces always occur in pairs. If
  object A exerts a force on object B, an equal but
  opposite force is exerted by object B on object
  A. (Physics 3rd Ed., Tipler, p. 78)
• The classic example of this is a rocket. It
  pushes away its burning exhaust gasses, and they
  in turn propel it forward. When I push on a desk
  or wall, it pushes back, but friction keeps me
  rooted to the spot. If I did this at an
  ice-skating rink, I would be pushed out into the
  rink.
• Newtons theory for gravity was understood.
  Essentially, Newton described gravity as a force
  of attraction between any objects with mass, and
  was able to formulate this mathematically.

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• Although Keplers laws were an important step in
  understanding the motion of the planets, they
  were still merely empirical rules obtained from
  the astronomical observations of Brahe. It
  remained for Newton to take the giant step
  forward and attribute the acceleration of a
  planet in its orbit to a force exerted by the sun
  on the planet that varied inversely with the
  square of the distance between the sun and the
  planet. Others besides Newton had proposed that
  such a force existed, but Newton was able to
  prove that a force that varied inversely with the
  square of the separation distance would result in
  the elliptical orbits observed by Kepler.

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• Newton then made the bold assumption that such a
  force existed between any two objects in the
  universe (before Newton, it was not even
  generally accepted that the laws of physics
  observed on earth were applicable to the heavenly
  bodies). (Physics 3rd Ed., Tipler, p. 299)
• There seems to be no reason to doubt the basic
  truth of the story of Newton and the apple that
  in 1666, having left Cambridge for a while on
  account of the Great Plague, he was moved by the
  fall of an apple to speculate if the Moon itself
  was falling toward the earth in a similar way.
  (Physics 3rd Ed., Tipler, p. 299)

16
Basic theories for electricity and magnetism were
known.

• Electric charge can be either positive or
  negative. Two objects that carry the same type
  of charge that is, two objects that are both
  positive or both negative repel each other, and
  two objects that carry opposite charges attract
  each other.(Physics 3rd Ed., Tipler, p. 599)
• Electric current is defined as the rate of flow
  of electric charge through a cross-sectional
  area. (Physics 3rd Ed., Tipler, p. 599)
• Basic theories for optics were understood.
• Optics is the branch of physics dealing with the
  nature and properties of light and vision.
  (Websters New World Dictionary, Third College
  Edition)
• Newton concluded that white light was composed of
  a mixture of a whole range of independent colors.
  (Optics, Hecht, p. 3)

17
Light

• There was debate as to its exact nature some
  viewed it as being made of particles, some viewed
  it as a wave.
•  Isaac Newton believed light to be particulate in
  nature. (Optics, Hecht, p. 3)
• Christiaan (this is the correct spelling of the
  name) Huygens (1629-1695) advanced the wave
  theory of light. He was able to derive the laws
  of reflection (the angle-of-incidence equals the
  angle-of-reflection) and refraction. (Optics,
  Hecht, pp. 3, 97)

18
The Law of Conservation of Mass

• The French chemist Antoine-Laurent Lavoisier
  (La-vwa-zee-ay) (1743-1794) had written a
  textbook in which he stated that in any closed
  system (one from which no mass was allowed to
  leave, and into which no mass was allowed to
  enter), the total amount of mass remained the
  same no matter what physical or chemical changes
  went on. (Asimovs Chronology of Science and
  Discovery, Asimov, pp. 240, 266)
• Fouquier-Tinvilles notorious words during the
  Revolution sent the chemist Lavoisier to the
  guillotine The Republic does not need any
  scientists. (wysiwyg//114/http//www.nobel.se/ph
  ysics/articles/curie)

19
Elements and Compounds

• Elements and compounds were known to exist.
•  An element can be informally defined as
  something with unique physical and chemical
  properties and something that cannot be broken
  down into any other substances. For example,
  gold, silver, and iron are elements.
•  A compound also is defined by its unique
  physical and chemical properties, but it can be
  broken down into simpler constituents (elements).
  For example, water can be broken down into
  hydrogen and oxygen, while table salt can be
  reduced to chlorine and sodium.
• Subsequent investigations proved that the
  smallest unit of a chemical substance such as
  water is a molecule. Each molecule of water
  consists of a single atom of oxygen and two atoms
  of hydrogen joined. (http//www.encarta.msn.com)

20

• Subsequent investigations proved that the
  smallest unit of a chemical substance such as
  water is a molecule. Each molecule of water
  consists of a single atom of oxygen and two atoms
  of hydrogen joined. (http//www.encarta.msn.com)
  
• The discoveries of both John Dalton (1808) and
  Amedeo Avogadro (1811) were important in this
  area of investigation.
• Essentially, Dalton returned to the Greek notions
  of Democritus that all matter was made up of
  tiny, indivisible particles. Dalton even used
  Democritus word atom for these particles. The
  Greeks thought that atoms differed among
  themselves in shape. Dalton, in whose time
  weight and measurements had grown important,
  maintained that the difference was one of weight,
  and he pioneered the concept of atomic weight.
  (Asimovs Chronology of Science and Discovery,
  Asimov, p. 287)

21
Avogadro

• The name "Avogadro's Number" is just an honorary
  name used to describe the calculated value of the
  number of atoms, and molecules in a gram mole of
  any chemical substance. It is 6.022 x 1023
  atoms/mol.

Avogadros Number
22
1820

• 1820- Several discoveries that year firmly
  established that moving charge (electric current
  in a wire, for example) produces a magnetic
  field.
• As part of a classroom demonstration, Hans
  Christian Oersted (1777-1851) had brought a
  compass needle near a wire through which a
  current was passing. The compass needle twitched
  and pointed neither with the current nor against
  it but in a direction at right angles to it.
  When Oersted reversed the direction of the
  current, the needle pointed in the opposite
  direction but still at right angles to the flow.
  (Asimovs Chronology of Science and Discovery,
  Asimov, pp. 308-309)