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Chapter 10
Our Star
Where does the sun’s energy come from?
1. Burning material
2. Chemical reactions
3. Fusion reactions
4. Fission reactions
5. Gravitational shrinking
Bhor model (H)
Schrödinger Model (H)
Atoms
• Atomic number - how many protons
• Atomic mass number - how many protons + neutrons
• Isotope - same atomic number, different mass number
Fundamental Forces
• Gravity - objects with mass
• Electromagnetic - objects with charge
• Strong Nuclear - protons, neutrons
• Weak Nuclear - electrons and stuff
What is the cause of sunspots?
1. Regions of higher temperature
2. Regions of lower temperature
3. Regions of different gas
4. Regions of dirt
The sun is most like:
1. A nuclear bomb
2. A gianormous bonfire
3. A lightbulb
4. A red hot piece of iron
What is the difference between a proton and a
neutron?
1. Proton is heavier
2. Neutron is heavier
3. Proton is positive, neutron is negative
4. Proton is light, neutron is a particle
5. Both 1 and 2
• How big? 100 x diameter, and 300,000 x more massive than Earth
• Star - luminous ball of gas
• Balance between gravitational forces and nuclear repulsion
•
light bulb is 100 Watts
• the sun is 4 x1026 Watts
• Or 400,000,000,000,000,000,000,000,000 Watts
What is the max power for 1 square meter on the surface of the Earth
(from the Sun)?
1. 1 Watt
2. 10 Watt
3. 100 Watt
4. 1000 Watt
5. 10,000 Watt
• At the Earth, we get a max of 1600 Watts per square meter
• Average is 250 W/m^2
• solar cells - efficiency is 30%-50% so...75 Watts per square meter
Which is hotter?
1. The interior of the Sun
2. The interior of the Earth
3. They are the same
Structure of the Sun
• Photosphere - the surface. This is where light can escape the sun
• below the photosphere, light can not escape
Thermal Energy Transfer
• Convection
• Conduction
• Radiation
Energy transport
• chromosphere (around 50,000 K)
• corona
What is pressure?
1. Force
2. Force per area
3. Area per force
4. Force per density
Pressure
• Show gas properties applet
E=mc2
• 1905 - Einstein
• 1 gram of mass is equivalent to a small nuclear weapon
• nuclear fusion
• Show fusion applet
From what part of the sun does the light we see come from?
1. The core
2. The radiative zone
3. The convection zone
4. The surface
Particle Inventory
• Electron - negative, very small mass
• Proton - positive, much more massive than electron (strong force)
• Neutron - neutral version of the proton
• Neutrino - neutral, very, very small mass,
• Positron - positive version of electron
• What is a plasma?
• Show proton-proton video
Some stuff
• Charge is conserved
• Energy is conserve (E = mc2)
• Mass not conserved
What is the same before and after a nuclear
reaction?
1. Mass
2. Charge
3. Energy
4. All of above
5. Both 2 and 3
6. None of the above
Why are solar neutrinos important?
1. They carry most of the energy from a reaction
2. They are the only way to observe the nuclear reactions
3. Because they are difficult to detect
Why are neutrinos so hard to detect?
1. Because they are neutral
2. Because they move so darned fast
3. Because they are so small
4. All of the above
5. None of the above
What would happen inside the Sun if a slight rise in core temperature led
to a rapid rise in fusion energy?
1.
A. The core would expand and heat up slightly.
2.
B. The core would expand and cool.
3.
C. The Sun would blow up like a hydrogen bomb.
Exploring the Core
• Neutrino - very weakly interacting. Hard to detect. But - they are the KEY.
• Neutrino detector
• Detected neutrinos are 3 times less than predicted
• Why? Either the Sun-model is wrong, or understanding of neutrinos is wrong
• Likely answer - they come in 3 versions
• Solar astronomy is important for particle physics
Solar Magnetic Activity
• Does the Sun have a magnetic field?
• Sunspots
• Sun Spots - dark appearing
• last a few days to over a month
• darker because they are cooler
• these are related to magnetic fields
• Charged particles spiral around magnetic fields
• spots come in pairs
Prominence
• Prominence - huge glowing gas plume that jut from chromosphere into corona
Flares
• Brief but bright eruptions of hot gas
• not bright enough to change daylight
• strong increase in x-ray and radio emissions
• can also shoot out gas (more than the solar wind)
Why sunspots?
• 1) Differential rotation
• 2) Distorted magnetic field
• Flares and solar wind - can produce aurora:
Solar wind
• High temp in corona gives some particles escape velocity
• amount of material lost due to wind is insignificant
• composed of H and He
Today: Production Cost of Electricity