What does the Second Law of Thermodynamics state? What is entropy? 17. What is s
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What does the Second Law of Thermodynamics state? What is entropy? 17. What is specific heat? How those it apply to the "Sea breeze" observed in coastal areas? 18. Know what the Hertzsprung-Russell (H-R) diagram is and where the Sun belongs in the diagram. 19. What are the following and where they belong on the H-R diagram? a. Main sequence b. Red Giant or Giants c. White Dwarf 20. After our Sun burns all the hydrogen in its core, it will become a? 21. Regarding our planets: a. Know the ordering of our planets in the Solar System from closest to furthest. b. Which planet does not have an atmosphere? c. What is Pluto's new classification?Explanation / Answer
16. The second law of thermodynamics states that for a thermodynamically defined process to actually occur, the sum of the entropies of the participating bodies must increase. In an idealized limiting case, that of a reversible process, this sum remains unchanged. A simplified version of the law states that the flow of heat is from a hotter to a colder body.
A thermodynamically defined process consists of transfers of matter and energy between bodies of matter and radiation, each participating body being initially in its own state of internal thermodynamic equilibrium. The bodies are initially separated from one another by walls that obstruct the passage of matter and energy between them. The transfers are initiated by a thermodynamic operation: some external agency intervenes[1] to make one or more of the walls less obstructive.[2] This establishes new equilibrium states in the bodies. If, instead of making the walls less obstructive, the thermodynamic operation makes them more obstructive, no transfers are occasioned, and there is no effect on an established thermodynamic equilibrium.
The law expresses the irreversibility of the process. The transfers invariably bring about spread, dispersal, or dissipation of matter or energy, or both, amongst the bodies. They occur because more kinds of transfer through the walls have become possible. Irreversibility in thermodynamic processes is a consequence of the asymmetric character of thermodynamic operations, and not of any internally irreversible microscopic properties of the bodies.
ENTROPY:
In thermodynamics, entropy (usual symbol S) is a measure of the number of specific realizations or microstates that may realize a thermodynamic system in a defined state specified by macroscopic variables. Most understand entropy as a measure of molecular disorder within a macroscopic system. The second law of thermodynamics states that an isolated system's entropy never decreases. Such a system spontaneously evolves towards thermodynamic equilibrium, the state with maximum entropy. Non-isolated systems may lose entropy, provided they increase their environment's entropy by that increment. Since entropy is a state function, the change in entropy of a system is constant for any process with known initial and final states. This applies whether the process is reversible or irreversible. However, irreversible processes increase the combined entropy of the system and its environment.
17. SPECIFIC HEAT:
The specific heat is the amount of heat per unit mass required to raise thetemperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.
Q=cmDT
Where
The sea has a greater heat capacity than land, so the surface of the sea warms up more slowly than the land's surface.As the temperature of the surface of the land rises, the land heats the air above it by conduction. The warm air is less dense and so it expands, decreasing the pressure over the land near the coast. The air above the sea has a relatively higher pressure, causing air near the coast to flow towards the lower pressure over land. The strength of the sea breeze is directly proportional to the temperature difference between the land and the sea. If a strong offshore wind is present, that is, a wind greater than 8 knots (15 km/h) and opposing the direction of a possible sea breeze, the sea breeze is not likely to develop.
During the day, the sun heats up both the ocean surface and the land. Water is a good absorber of the energy from the sun. The land absorbs much of the sun’s energy as well. However, water heats up much more slowly than land and so the air above the land will be warmer compared to the air over the ocean. The warm air over the land will rise throughout the day, causing low pressure at the surface. Over the water, high surface pressure will form because of the colder air. To compensate, the air will sink over the ocean. The wind will blow from the higher pressure over the water to lower pressure over the land causing the sea breeze. The sea breeze strength will vary depending on the temperature difference between the land and the ocean.
At night, the roles reverse. The air over the ocean is now warmer than the air over the land. The land loses heat quickly after the sun goes down and the air above it cools too. This can be compared to a blacktop road. During the day, the blacktop road heats up and becomes very hot to walk on. At night, however, the blacktop has given up the added heat and is cool to the touch. The ocean, however, is able to hold onto this heat after the sun sets and not lose it as easily. This causes the low surface pressure to shift to over the ocean during the night and the high surface pressure to move over the land. This causes a small temperature gradient between the ocean surface and the nearby land at night and the wind will blow from the land to the ocean creating the land breeze.
18. The sea has a greater heat capacity than land, so the surface of the sea warms up more slowly than the land's surface. As the temperature of the surface of the land rises, the land heats the air above it by conduction. The warm air is less dense and so it expands, decreasing the pressure over the land near the coast. The air above the sea has a relatively higher pressure, causing air near the coast to flow towards the lower pressure over land. The strength of the sea breeze is directly proportional to the temperature difference between the land and the sea. If a strong offshore wind is present, that is, a wind greater than 8 knots (15 km/h) and opposing the direction of a possible sea breeze, the sea breeze is not likely to develop.
These diagrams, called the Hertzsprung-Russell or HR diagrams, plot luminosity in solar units on the Y axis and stellar temperature on the X axis, as shown below.
Notice that the scales are not linear. Hot stars inhabit the left hand side of the diagram, cool stars the right hand side. Bright stars at the top, faint stars at the bottom. Our Sun is a fairly average star and sits near the middle.
A plot of the nearest stars on the HR diagram is shown below:
Most stars in the solar neighborhood are fainter and cooler than the Sun. There are also a handful of stars which are red and very bright (called red supergiants) and a few stars that are hot, but very faint (called white dwarfs). We will see in a later lecture that stars begin their life on the main sequence then evolve to different parts of the HR diagram.
Most of the stars in the above diagram fall on a curve that we call the main sequence. This is a region where most normal stars occur. Normal, in astronomy terms, means that they are young (a few billion years old) and burning hydrogen in their cores. As time goes on, star change or evolve as the physics in their cores change. But for most of the lifetime of a star it sits somewhere on the main sequence.
Several regions of the HR diagram have been given names, although stars can occupy any portion. The brightest stars are called supergiants. Star clusters are rich in stars just off the main sequence called red giants. Main sequence stars are called dwarfs. And the faint, hot stars are called white dwarfs.
The spectral classification types were more accurate then attempts to measure the temperature of a star by its color. So often the temperature scale on the horizontal axis is replaced by spectral types, OBAFGKM. This had the advantage of being more linear than temperature (nicely spaces letters) and contained more information about the star than just its temperature (the state of its atoms).
19.
20. When the Sun runs out of hydrogen to fuse, the balance tips in the favor of gravity, and the star starts to collapse. But compacting a star causes it to heat up again and it is able fuse what little hydrogen remains in a shell wrapped around its core.
Medium mass stars, like our Sun, live by fusing the hydrogen within their cores into helium. This is what our Sun is doing now. The heat the Sun generates by its nuclear fusion of hydrogen into helium creates an outward pressure. In another 5 billion years, the Sun will have used up all the hydrogen in its core.
This situation in a star is similar to a pressure cooker. Heating something in a sealed container causes a build up in pressure. The same thing happens in the Sun. Although the Sun may not strictly be a sealed container, gravity causes it to act like one, pulling the star inward, while the pressure created by the hot gas in the core pushes to get out. The balance between pressure and gravity is very delicate.
When the Sun runs out of hydrogen to fuse, the balance tips in the favor of gravity, and the star starts to collapse. But compacting a star causes it to heat up again and it is able fuse what little hydrogen remains in a shell wrapped around its core.
This burning shell of hydrogen expands the outer layers of the star. When this happens, our Sun will become a red giant; it will be so big that Mercury will be completely swallowed!
When a star gets bigger, its heat spreads out, making its overall temperature cooler. But the core temperature of our red giant Sun increases until it's finally hot enough to fuse the helium created from hydrogen fusion. Eventually, it will transform the helium into carbon and other heavier elements. The Sun will only spend one billion years as a red giant, as opposed to the nearly 10 billion it spent busily burning hydrogen.
We already know that medium mass stars, like our Sun, become red giants. But what happens after that? Our red giant Sun will still be eating up helium and cranking out carbon. But when it's finished its helium, it isn't quite hot enough to be able to burn the carbon it created. What now?
Since our Sun won't be hot enough to ignite the carbon it its core, it will succumb to gravity again. When the core of the star contracts, it will cause a release of energy that makes the envelope of the star expand. Now the star has become an even bigger giant than before! Our Sun's radius will become larger than Earth's orbit!
The Sun will not be very stable at this point and will lose mass. This continues until the star finally blows its outer layers off. The core of the star, however, remains intact, and becomes a white dwarf. The white dwarf will be surrounded by an expanding shell of gas in an object known as a planetary nebula. They are called this because early observers thought they looked like the planets Uranus and Neptune. There are some planetary nebulae that can be viewed through a backyard telescope. In about half of them, the central white dwarf can be seen using a moderate sized telescope.
21.
a) First the quick facts: Our Solar System has eight “official” planets which orbit the Sun. Here are the planets listed in order of their distance from the Sun:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
b) Mercure doesn’t have atmosphere
c) Dispassionately put, the status of Pluto and the Edgeworth-Kuiper Belt objects is a question of classification: of moving an object from one class to another with new knowledge in the case of the former, or of classifying newly discovered objects in the case of the latter. Classification is an important part of science, and has a long and distinguished history, especially in biology. As Linnaeus stated in his Systema Naturae (1735), "The first step in wisdom is to know the things themselves. This notion consists in having a true idea of the objects; objects are distinguished and known by classifying them methodically and giving them appropriate names. Therefore, classification and name-giving will be the foundation of our science." And as Stephen J. Gould has said more recently in connection with biology, "Taxonomies are reflections of human thought; they express our most fundamental concepts about the objects of our universe. Each taxonomy is a theory about the creatures [for astronomy, the objects] that it classifies.” Indeed, this is why Pluto has raised so much emotion.
Classification in biology has been proceeding apace for almost three centuries since Linnaeus, and some of biology's most distinguished thinkers, including recently deceased Harvard Professor Ernst Mayr, have discussed its importance and its intricacies. Controversies abound at many taxonomic levels, including the top level of "Kindgom" or "Domain". But no biologist seriously questions the value of classification. Therefore the IAU was following the best tradition of science, not only in classifying Pluto, but also in changing classifications based on new knowledge. Creating a new class of objects, or moving objects to another class, is not unusual either in biology or astronomy. Historically astronomers have often had to reclassify objects with the growth of knowledge. There was the curious case of Chiron, discovered in 1979, thought at that time to be a comet or an asteroid. It is now classified as both, an intermediate object called a Centaur. In the case of quasars, originally called 'quasi-stellar objects,' the objects were moved from the realm of the stars to the realm of the galaxies when they were found to exist at the cores of active galaxies. Similarly, recently the reverse happened: the sources of short period gamma ray bursts were shown to be galactic rather than extragalactic, in other words, in the realm of the stars rather than the realm of the galaxies. And if we step back beyond astronomy, we see the same thing happening, historically and presently, in biology.
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