A pistoncylinder device initially contains 15 ft3 of helium gas at 25 psia and 708F. Helium is now compressed in a polytropic process (PVn 5 constant) to 70 psia and 3008F. Determine (a) the entropy change of helium, (b) the entropy change of the surroundings, and (c) whether this process is reversible, irreversible, or impossible. Assume the surroundings are at 708F.
Chapter 19: Our Galaxy The Milky Way Revealed o What does our galaxy look like Dusty and gas obscure our view of the galaxy. Looks like a disk 100,000 light-years in diameter Bulge in the middle Globular Clusters in the halo o Halo is outside the disk Has spiral arms: different color from bulge o Blueish: bigger, younger stars Barred Spiral The bulge is elongated like a bar is in it. o How do stars orbit in our galaxy Stars in the disk travel in circles with little up and down motions Halo stars go above the disk randomly Bulge stars move in random paths We have a 230 million-year orbit Orbital Velocity Law The orbital speed and radius of an object on a circular orbit around the galaxy tells us the mass within that orbit. Galactic Recycling o How is gas recycled in our galaxy Star-Gas-Star Cycle n o Wh er dIonization nebulae are found around short-lived high-mass stars Shows star activity None in halo, or bugle o No stars being formed Reflection nebulae scatters the light from stars Spiral Arms of the galaxy is where most of the star formation takes place History of the Milky Way o What clues to our galaxy’s history do halo stars hold Halo Stars are older than our galaxy Formed first then stopped o Giant cloud makes the halo stars are it contracts. Center of our galaxy o What lies in the center of our galaxy Lots of stars orbit around it We believe it is a black hole Lots of mass Invisible Small Region See X-ray bursts, but no accretion disk l