Do Activity

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Do Activity 41 (pages 153-155),Questions 1
through 16

• then well have a clicker quiz

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9. Which star in Figure 4 has the highest
temperature?

• Star A
• Star B
• Star C

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11. If a star cools, it shrinks because

• Lower temperature means less volume
• Fusion reactions which occur at a lower
  temperature convert less mass into energy
• Lower temperature means less pressure to resist
  gravity

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13. When you expend energy to blow up a balloon,
where does that energy go?

• Mostly into heating the air in the balloon
• Mostly into elastic energy stored in the material
  of the balloon
• Nowhere energy is conserved

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Reading Quiz using Clickers
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What powers the sun?

• The fission of hydrogen into helium, which
  converts some mass into energy
• The fission of helium into hydrogen, which
  converts some mass into energy
• The complete conversion of the mass of some
  hydrogen into energy
• The fusion of hydrogen into helium, which
  converts some mass into energy

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What conditions are required for nuclear fusion
of hydrogen to occur?

• Temperature of millions of degrees
• High density
• Uranium present
• All of the above
• 1 and 2 only
• 1 and 3 only

8
Why do sunspots appear dark in pictures of the
Sun?

• They are holes in the solar surface through which
  we can see through to deeper, darker layers of
  the Sun.
• They are thick clouds of cool gas which block the
  light from underneath.
• They are too cold to emit any visible light.
• They are actually bright, but appear dark against
  the even brighter regions which surround them.

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What is the Suns structure?
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(No Transcript)
11
Photosphere Visible surface of Sun (not solid)
5,800 Kelvin 5,500 Celsius
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10.2 Nuclear Fusion in the Sun

• Our Goals for Learning
• How does nuclear fusion occur in the Sun?
• How does the energy from fusion get out of the
  Sun?
• How do we know what is happening inside the Sun?

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How does nuclear fusion occur in the Sun?
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High temperature enables nuclear fusion to happen
in the core
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Sun releases energy by fusing four hydrogen
nuclei into one helium nucleus, which has less
mass. The difference in mass is released as
energy, in the form of gamma-ray photons.
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(No Transcript)
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IN 4 protons OUT 4He nucleus 2 neutrinos 2
gamma rays 2 positrons (which collide with 2
electrons, making more gamma rays) Total mass
is 0.7 lower (4 million tons of matter
converted to energy every second inside the Sun!)
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Solar Thermostat
Rise in core temperature causes fusion rate to
rise, so core expands and cools down
Decline in core temperature causes fusion rate to
drop, so core contracts and heats up
Structure of the Sun
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How does the energy from fusion get out of the
Sun?
20
Energy gradually leaks out of radiation zone in
form of randomly bouncing photons it takes
millions of years for this to happen.
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(No Transcript)
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(No Transcript)
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How do we know what is happening inside the Sun?
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We learn about the Sun's interior by

• Making mathematical models
• Observing solar vibrations (sun quakes'), just
  like we learn about the Earth's interior from
  earthquakes
• Observing solar neutrinos, a kind of particle
  that rarely interacts with other particles

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Patterns of vibration on surface tell us about
what Sun is like inside Results agree very well
with mathematical models of solar interior
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Neutrinos created during fusion fly directly
through the Sun Observations of these solar
neutrinos can tell us whats happening in core
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Solar neutrino problem Early searches for solar
neutrinos failed to find the predicted number
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Solar neutrino problem Early searches for solar
neutrinos failed to find the predicted
number More recent observations with the Sudbury
Neutrino Observatory (pictured) in northern
Ontario find the right number of neutrinos, but
some have changed form, which allowed them to
escape earlier searches.
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What have we learned?

• How does nuclear fusion occur in the Sun?
• Fusion of hydrogen into helium, which occurs via
  the protonproton chain. Gravitational
  equilibrium acts as a thermostat that keeps the
  fusion rate steady.

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What have we learned?

• How do we know what is happening inside the
  Sun?
• theoretical models
• use known laws of physics and then check the
  models against observations and studies

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What have we learned?

• How does the energy from fusion get out of the
  Sun?
• Energy moves through the deepest layers of the
  Sunthe core and the radiation zonein the form
  of randomly bouncing photons. After energy
  emerges from the radiation zone, convection
  carries it the rest of the way to the
  photosphere, where it is radiated into space as
  sunlight.

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Quiz using Clickers
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What powers the sun?

• The fission of hydrogen into helium, which
  converts some mass into energy
• The fission of helium into hydrogen, which
  converts some mass into energy
• The complete conversion of the mass of some
  hydrogen into energy
• The fusion of hydrogen into helium, which
  converts some mass into energy

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Why is the Sun very dense on the inside?

• Denser materials sank to the center
• It formed from dense material
• Pressure of the overlying gas keeps the density
  high

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Why are very high temperatures required for
nuclear fusion to occur?

• It takes energy to make energy
• High temperatures and speeds involve Einsteins
  theory of relativity
• Only high-speed protons approach each other close
  enough for nuclear forces to bind them
• They arent. When fusion happens at room
  temperature it is called cold fusion

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By the time photons reach the surface of the Sun,
they are mostly

• Infrared light (heat)
• Visible light
• Ultraviolet light
• X rays
• Gamma rays

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How do photons get from the core of the Sun to
the surface of the Sun?

• They travel at lightspeed
• They are absorbed, then emitted by many atoms
• They are conducted (heat conduction)
• Gamma rays
• X rays
• None of the above