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Lecture 19

# Lecture 19 - Three ways energy y is transported a Radiation...

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Lecture 19 Mechanical properties of stars a) Gravity- holds stars together and makes them circular b) Gas pressure- prevents star from collapsing in on itself i) Boyle’s Law- pressure is proportional to density (blowing up balloon) ii) Charles’ Law- pressure is proportional to temperature (can implosion) iii) Compressing gas causes it to heat up Kinetic Theory of Gases- by James Clerk Maxwell a) “Tiny elastic particles (atoms) in constant motion” b) Allows us to understand i) Random thermal motions create pressure ii) Temperature is a measure of speed (kinetic energy) iii) Explains Charles’ and Boyle’s Law iv) Explains hydrostatic equilibrium Thermal Equilibrium a) Energy flows from hot to cool b) As much heat is flowing into the sun from an underneath layer as heat leaves the surface of it c) Temperature profile of star- determined from condition that temperature at the surface is constant

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Unformatted text preview: Three ways energy y is transported a) Radiation- heat hits you directly b) Conduction- heat transfers or flows along the object being heated c) Convection- circulation of air Opacity a) Level at which matter absorbs radiation b) Sun opacity depends on interior electron scattering c) Opacity in a region determines rate at which energy flows i) If opacity is too large, we get convection Sun convection a) Core radiates the rest of the layers of the sun b) Main transport mechanisms are radiation and convection Mass-Luminosity relationship- by Sir Arthur Eddington a) As mass increases gravity increases and so pressure must increase as well b) Charles law then says that temperature increases which S-B says that luminosity must increase then Why is a star hot? a) Stars radiate because they’re hot b) Why? They have an energy source...
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