Are these "phase transitions" that occurred when some critical number of chemicals in a primeval soup was exceeded, or when the network of neurons in a brain become great enough in number and in connectivity that something novel appeared, an "intelligence" phase?
Gravity tries to pull all the mass of a star into its center but this inward force is opposed by the large outward pressure of the small stellar core, which in turn arises from the high temperature of the core caused by fusion reactions. But even in the absence of hot fusion reactions, the inward pull of gravity becomes opposed by a new mechanism, which is a quantum mechanical repulsion of the freely moving electrons in the white dwarf that arises when many electrons are crowded into a sufficiently small volume. This repulsion exists even at absolute zero and has nothing to do with electrical repulsion, it is a consequence of a quantum mechanical exclusion principle that prevent two electrons with the same quantum state from being near one another.
In this case, the white dwarf explodes with astounding energy with as much energy as about 10 10 stars over a period of about a week!
Because all white dwarf explosions are essentially identical they are all triggered when the Chandrasekhar limit is just exceeded , their explosions have provided astronomers with accurate beacons that allow distances to be measured accurately over long distances. It is in fact measurements based on white dwarf explosions that allowed astronomers to detect the accelerated expansion of the entire universe, leading to one of the big mysteries of current science, which is what is causing the accelerated expansion and whether it will ever stop.
Skip to main content Thermal Physics PHYSICS Thermal properties of matter treated using the basic concepts of entropy, temperature, chemical potential, partition function, and free energy. Textbook Daniel V.
PHYS 143: Mechanics and Thermal Physics
Schroeder, "An Introduction to Thermal Physics. Questions about Thermal Physics. The Celsius Temperature Scale. Why a Gas Exerts a Pressure. Why the Pressure Increases with Increasing Temperature. Why the Pressure Increases when the Gas is Compressed. Distribution of Molecular Speeds.
The Heat Capacity of a Body. The Specific Heat Capacity of a Substance. To Heat Linear Expansivity. Changes of State or Phase Changes. If a gas expands against the atmosphere, it must do work to push back the atmosphere. Its particles lose energy and move more slowly, so its temperature falls. How would such changes be observed?
That is, what does a change in U represent? Note that it affects not just temperature but also possibly the state of a gas. There are a number of possible demonstrations of the First Law. Simple and dramatic ones include commercial devices that let you compress a cylinder of air rapidly and ignite a small wad of cotton. A more conventional alternative is to compress the air in a bicycle pump and to observe the rise in temperature. Episode Warming up a gas by speeding up its particles Word, 46 KB.
The reverse effect is to demonstrate the formation of dry ice from a CO 2 cylinder, letting the gas expand against air pressure. You will need to consult the relevant safety documents for this. Episode Formation of dry ice from a carbon dioxide cylinder Word, 79 KB.
Thermal Physics Tutorial 1
You may also have the equipment for a quantitative analysis. This usually involves a friction drum or wheel and compares mechanical work done against a friction force to the rise in temperature of the system. An alternative system allows mechanical work to be compared with energy supplied electrically. Episode Doing mechanical work Word, 48 KB. Episode Mechanical and electrical heating Word, 50 KB. This simulation of an adiabatic change may be useful, but beware the different notation used for internal energy:.
Boston University Physics Department. The conservation of energy underlies our modern understanding of physics but also has important implications for our use of energy resources. In particular, the idea that mechanical working can fill a very diffuse thermal store of the surroundings is a very practical issue. With little quantitative work in this section, students could be set questions on sensible use of energy resources or the mechanics of power stations.
Try to get them to emphasise the difference in meaning between conserving energy as in not wasting it and the scientific meaning of conservation. If you have a model steam engine it would be excellent to show this and consider the energy flow through the system. Emphasise the wasted energy as steam is emitted from the chimney for example. If you do not have a steam engine, try to find a video or other resources relating to the energy flow through a power station.
In all cases there should be energy from the fuel transferred to the working fluid usually water that generates steam. The steam drives a turbine and then is condensed and returned to the boiler.
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A significant proportion of the energy of the steam is not delivered to the turbines and it is then wasted in heating up the coolant in the condenser. That coolant may then itself be used as a source of energy in Combined Heat and Power stations improving the overall efficiency of the power station. Use the web or printed information from energy companies to find out about the efficiency of different types of power stations. Because energy is conserved.
If not, lead them to thinking about systems where heating is the intended change — such as a radiator or electrical fire. How does a coal fire compare energy loss up the chimney?
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Ultimately, justification of the Second Law of thermodynamics rests on an understanding of entropy. Without a full-blown mathematical proof, which is inappropriate at this level, it is necessary to rely on assertion and justification by reason. A simple statement of the Second Law is that you cannot have a process whose only effect is to use a thermal store of energy to do work.
If you could, you could build a car which extracted energy from the air and drive along without needing petrol. This limitation is fundamental not merely a practical constraint. In a power station the working fluid water or steam is allowed to expand through the turbines and so drive them. Afterwards the expanded steam needs to be returned at low pressure by cooling in order to complete a cycle — to put it back as it was before it entered the boiler.
Hence the need to cool the steam in the condenser. This energy is not useful. Thus, although we can use some energy from a thermal store to do work we cannot extract all of it. In this equation T is in K , the absolute temperature. Finally, you may need to mention the heat pump. This is simply a heat engine operated in reverse.
It drives energy from a cold reservoir to a hot one by putting work in. The details are not needed, but a refrigerator is an example. Heat pumps are sometimes used to heat houses in cold climates.
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They can be very effective. Episode Student questions; calculating efficiency Word, 27 KB. Energy must be supplied or rejected to increase or decrease the temperature of a material. Here is how to calculate how much. Up until this point the link between internal energy and temperature has been qualitative, except for gases. In order to extend the discussion to solids and liquids we need to get more quantitative in two ways. One is to discuss how much the temperature of a body changes when its internal energy in increased by a certain amount. The other is to ask what happens when a substance changes phase from a solid to a liquid or liquid to a gas.
Start by introducing the equation for specific heat capacity c SHC and defining the terms. The word specific is an old fashioned way of saying per unit mass. Work through a simple calculation. Understanding this equation will help solidify ideas about temperature and energy and how they differ. A possible analogy was supplied by Richard Feynman.