Follow the energy Part 2

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Follow the energy (Part 2)

• Lecture 7
• Solar Radiation

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Proton-Proton chain
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The Suns Energy Source is ThermonuclearFusion
in its Core

• Proton-proton chain
• Four hydrogen nuclei fuse to form a single
  helium nucleus
• Thermonuclear fusion occurs only at the very high
  temperatures at the Suns core
• Will continue to heat the Sun for another 5
  billion years

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Solar Evolution
Collapse of the hydrogen molecular cloud
Earth will be likely destroyed
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Solar energy from hydrogen fusion
Solar Radiation
Photosynthesis
Climate
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Radiation What is solar radiation? Energy is
transferred by electromagnetic waves Electromagne
tic waves are not limited to visible light
(sunlight) only. X-rays, Radio waves, Microwaves
are all electromagnetic waves
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http//www.astronomynotes.com/light/s2.htm
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Properties of Waves All electromagnetic waves
travel at the same speed The speed of light
300,000 Km/s
crest
trough
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Properties of Waves
Wavelength (length/cycle)
crest
trough
Wavelength (?) the length of one complete cycle
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Properties of Waves
Wavelength (length/cycle)
crest
Amplitude
trough
Amplitude 1/2 height between trough and crest
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Properties of Waves
Wavelength (length/cycle)
crest
Amplitude
trough
Frequency (?) the number of cycles/second
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Speed wavelength x frequency c ?
? (length/second) (length/cycle) x
(cycle/second)
Hence, ? c / ? and ? c / ?
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Energy of the Electromagnetic Radiation At times
an electromagnetic wave behaves like a stream of
particles Photon - a single particle or pulse,
of electromagnetic radiation Energy of a photon
is proportional to frequency, and inversely
proportional to wavelength E h ?
h (c/ ?) where h Plancks constant
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Electromagnetic Spectrum
? (?m)
(? micro 10-6)
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Electromagnetic Spectrum
visible light
0.7 to 0.4 ?m
? (?m)
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Electromagnetic Spectrum
visible light
ultraviolet
? (?m)
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Electromagnetic Spectrum
visible light
ultraviolet
infrared
? (?m)
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Electromagnetic Spectrum
visible light
ultraviolet
infrared
x-rays
microwaves
? (?m)
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Electromagnetic Spectrum
visible light
ultraviolet
infrared
x-rays
microwaves
High Energy
Low Energy
? (?m)
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Visible Light (VIS) 0.7 to 0.4 ?m Our eyes are
sensitive to this region of the
spectrum Red-Orange-Yellow-Green-Blue-Indigo-Vio
let
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Why plants are green?

• Photosynthesis mostly uses visible radiation
• Green plants effectively absorb violet blue and
  red radiation. Green wavelengths are not absorbed
  effectively and that is why plants look green
• Red algae absorb blue-green radiation and that is
  why algae looks red.

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Categories of UV Radiation
Name Wavelength(s) Biological Effect UV-A gt 320
nm (0.32 ?m) harmful(?) UV-B 290-320
nm Harmful UV-C lt 290 nm Very harmful,
but blocked by O3 and O2
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UV-B concern

• DNA absorb UV-B
• Animals skin cancer, cataracts, suppressed
  immune system .
• Plants photosynthesis inhibition, leaf
  expansion, plant growth

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• C-T mutation
• UVB photons excite DNA
• Adjacent C bases form a dimer
• DNA polymerase reads CC dimer
• as AA
• 4) New strand would get TT instead of GG

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Infrared Radiation (IR) We cant see IR, but we
can feel it as radiant heat Lower energy than
visible light
(An image of a human hand, taken in the infrared,
and displayed in false color. Here white and
yellow correspond to hot regions, blue and green
to cool regions.)
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Solar Spectrum The sun emits radiation at all
wavelengths Most of its energy is in the
IR-VIS-UV portions of the spectrum 50 of the
energy is in the visible region 40 in the
near-IR 10 in the UV
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Wavelength (m)
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Questions

• Why is the most of the solar radiation emitted at
  visible wavelengths? Why not at X-rays or
  microwaves?
• What determines the total luminosity of a star?
• To answer these questions we need to understand
  the concept
• of temperature

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• Thermal Energy
• All matter is composed of atoms or molecules,
  which are in constant motion
• Molecular or atomic motion thermal energy
• Heating causes atoms to move faster, which
  represents an increase in thermal energy.
• Temperature is a measure of thermal energy a
  measure of the average chaotic motion of atoms or
  molecules

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To measure temperature we need to agree on the
temperature scale.
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• Relative size of a degree F vs. a degree
  C--compare
• the number of degrees between freezing and
  boiling
• 100oC 180oF
• ? 1oC 1.8oF 1oK

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Temperature Scales Fahrenheit , Celsius and
Kelvin (oC x 1.8) 32 oF (oF - 32) / 1.8
oC oC 273 oK
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Back to Radiation
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Blackbody Radiation
Planck function
Blackbody radiationradiation emitted by a body
that emits (or absorbs) equally well at all
wavelengths
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• Basic Laws of Radiation
• All objects emit radiant energy (electromagnetic
  waves).
• Hotter objects emit more energy than colder
  objects. The amount of energy radiated is
  proportional to the temperature of the object
  raised to the fourth power.
• ? This is the Stefan Boltzmann Law
• F ? T4
• F flux of energy (W/m2)
• T temperature (K)
• ? 5.67 x 10-8 W/m2K4 (a constant)

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• Basic Laws of Radiation
• All objects emit radiant energy.
• Hotter objects emit more energy than colder
  objects (per unit area). The amount of energy
  radiated is proportional to the temperature of
  the object.
• The hotter the object, the shorter the wavelength
  (?) of emitted energy.
• ?This is Wiens Law
• ?max ? 3000 ?m
• T(K)

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? Stefan-Boltzmann law F ? T4 F flux
of energy (W/m2) T temperature (K) ? 5.67
x 10-8 W/m2K4 (a constant) ? Wiens law
?max ? 3000 ?m T(K)
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Electromagnetic Spectrum
visible light
ultraviolet
infrared
x-rays
microwaves
High Energy
Low Energy
? (?m)
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• Blue light from the Sun is removed from the beam
  
• by Rayleigh scattering, so the Sun appears
  yellow
• when viewed from Earths surface even though
  its
• radiation peaks in the green

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Stellar spectrum is important for life!

• Photosynthesis requires visible radiation
  (0.4-0.7 microns)
• Photosynthesis can be inhibited by UV radiation
  (UV-B)
• Organisms have to protect themselves from UV but
  have to be able to absorb visible radiation at
  the same time.