Tag Info

Hot answers tagged

74

Thus, the air molecules contribute a small portion of their kinetic energy to the paddle, which is then expended as heat on the other side of the border, making the air molecules on the left colder, while air molecules on the right heat up. Doesn't this mean a decrease in entropy? Yes it does. However, we need to take the thermal noise of the resistor ...


45

Sort of, yes. Ice water is, in fact, a negative-calorie foodstuff and could be used to lose some weight. Fats contain about 37 kJ/gram of energy, drinking one glass of ice water will burn about 37 kJ or up to three times more if you eat some crushed ice as part of drinking the water: so that's 1 gram of fat burned per drink, up to 2-3 if you eat ice. The ...


30

Do black holes violate the first law of thermodynamics? No. See Wikipedia re the first law of thermodynamics: "The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed ...


13

Chemical bonds, just like nuclear bonds, have an associated mass to them. Nucleons make up most of the mass of the atom, with about 938 MeV per nucleon. Nuclear binding energy is usually on the scale of a few MeV, meaning that the mass difference during a nuclear reaction will be usually under 1% of the mass of one proton. Chemical reactions, on the other ...


11

There are three things to consider here: Mass of combustion products Since combustion is by definition the chemical combination of the fuel with oxygen, the mass will go up. If we burn a material with a volatile oxide, such as carbon, the mass of solid material remaining will go down (but really the lost mass is present in the atmosphere.) If we burn a ...


10

The internal energy of an ideal gas is independent of volume when considered as a function of volume and temperature. If we choose to consider internal energy as a function of volume and some other thermodynamic variable we will find that the dependence of the energy on volume will change because we are keeping a different variable constant as volume is ...


5

Practically speaking, diamond has the highest thermal conductivity of any "reasonable" material, about 5 times greater than copper. Additionally, its specific heat is about 30% greater than copper or brass, but about 10% that of water. As a result, a diamond will heat up faster than just about anything else, particularly when immersed in a liquid like water ...


5

According to the second law of thermodynamics, sustained cooling below the ambient temperature requires work. The fridge's electric motor does this work to cool the air inside the fridge, in the same time it has to warm air outside the fridge - this is how one can "huddle next to a fridge" to keep warm (you can easily find the warm place of your fridge, ...


4

The body surely needs to produce energy to heat the water one drinks - and it will heat water because almost everything in the human body is about 37 °C - but whether one loses weight in the process depends on whether the energy is taken from the accumulated fat, or from piles of extra food one devours because he or she is hungry and can't resist. ;-) The ...


4

The answer depends on the definition of the system. Imagine a piece of paper burning in air to produce carbon dioxide and water. If the system includes just the paper the system will lose a lot of mass as CO2 and water are given off. If the system is the paper, CO2 and water in a glass bowl in thermal contact with the rest of the universe, the system will ...


4

If you add mass keeping the volume constant, the pressure would change. When a source says that pressure is independent of mass, it means that pressure is independent of mass if you keep the density constant, not the volume. The idea is that if you take two identical copies of a system, then combine them to make a system twice as large, extensive ...


4

The proof behind Carnot's upper limit posed on the efficiency of heat engines is more robust than this. The quotes you've pasted are among the various statements of the second law of thermodynamics. Here I'll sketch for you some of the ideas of the proof, mainly to show where these formulations (related to Carnot) of the second principle come from. ...


4

If you have a glass of water, every molecule of water is under the influence of the gravitational potential field. Each molecule pushes down on the molecules below. The molecules of water near the bottom of the glass experience the downward force from all molecules above them (each molecule transfers the force downward). If you made a hole near the bottom of ...


3

Dr. Robitaille says that blackbody radiation is not universal, even inside cavities where the surfaces are all at thermal equilibrium. That is highly controversial since the electromagnetic fields in a cavity are usually considered as an additional substance, called a "photon gas" which is also at thermal equilibrium and hence has a temperature. This ...


3

A neutron has an up quark with charge +2/3 and two down quarks each with charge -1/3. It has a magnetic moment and it does interact with electromagnetic radiation. So the premise seems incorrect.


3

As it was explained in one of Halliday's books, the reason is that the black dress heats the air inside it up, thus causing a continuous flow of air in between the skin and the dress. The cold air flows in from below, gets heaten up, and gets out from above, providing a continuous ventilation.


3

I will not answer your question directly; only give you some tools that should help you answer the question (in practice) yourself. To focus the attention, find below a typical heating/cooling diagram for a frozen pure substance. The vertical axis marked $T$ represents temperature (in degrees Celsius). Three significant temperatures are indicated on the ...


3

A recent work that uses nanothermodynamics and includes a computational investigation of the kind you are asking about for an Ising lattice: R.V. Chamberlin, The Big World of Nanothermodynamics Sec.5 of the following paper makes a reference to another paper that appears to have tested the limits of usual thermodynamics in single polymer stretching ...


3

The simple answer, which is what I think you're hoping for is the following: At constant volume, the system (by definition) is not able to do work on the surroundings because work involves a change in volume. All the heat you put in is spent raising the temperature (internal energy). At constant pressure, some of the energy you put in goes into raising the ...


3

Is it possible to measure the temperature of something using sound...? Yes, it is not only possible, it is available commercially. It is especially useful in harsh environments where conventional temperature probes might not survive. For example, TMT makes an acoustic system for measuring 2-D temperature distributions in blast furnaces: The ...


3

Mirrors and lenses cannot do what you ask. Light has a specific intensity, meaning a power per unit area per unit solid angle per unit wavelength. Mirrors and lenses can never increase the specific intensity. As an example, consider using a lens to focus sunlight onto a target. The specific intensity of the sunlight is the same with or without the lens. ...


3

Even though the overall efficiency reduces... The efficiency doesn't "reduce". It just doesn't increase as much as one might, at first, hope. Why don't people use this method? It is widely used. When two heat engines are used this way, it is called a "combined cycle". Example 1 You can, for example, buy a combined-cycle power plant from ...


3

Even when you're hot, the body keeps producing heat, which it then goes through the trouble of shedding. Unless you were already very cold, the heat to warm your water and food intake will come out of this surplus. The body may even save energy because it doesn't need to shed as much heat. If you're wiling to be very cold all the time, you can do so more ...


3

If you start with a monatomic gas then the only degrees of freedom available are the three translational degrees of freedom. Each of them absorbs $\tfrac{1}{2}kT$ of energy, so the specific heat (at constant volume) is $\tfrac{3}{2}k$ per atom or $\tfrac{3}{2}R$ per mole. If you move to a diatomic molecule there are two rotational modes as well - only two ...


3

Many people have the misconception that only infrared radiation creates heat. Actually electromagnetic radiation over all frequencies carries energy. The shorter the wavelength, the higher the energy. Different elements and compounds (or molecules and atoms) have different resonant frequencies and so electromagnetic radiation of the same frequency tends to ...


2

We live in the age of measurements and observations and specific mathematical theories that fit measurements and observations beyond any doubt. Photons are elementary particles. . They have zero mass, and other characteristics which separate them from other elementary particles . Can photons lose a small amount of energy over time when traveling large ...


2

Yes, photons do lose energy because of the expansion of space. Their wavelengths are increased by a factor of $(1+z)$ between when they were emitted at redshift $z$ and when we detect them now. Their energies are therefore decreased by a similar amount. The "tired light" interpretation of this effect has been discussed, debated and disproved. In my opinion, ...


2

A macrostate is characterized by certain definite values of macroscopic variables (ones that you measure with tools of human scale; often called thermodynamic variables). For a simple hydrostatic system you might choose to have the whole system in the liquid state with temperature between $T$ and $T + \mathrm{d}T$ and pressure between $P$ and $P + ...


2

In addition to the other reply, it can be added that by definition, in an ideal gas, there is no interaction between molecules, and therefore no potential energy associated with the average distance. This is why in a Joule-Thomson expansion, there is no change in the temperature of the gas: only the volume changes, no work is extracted, and the average speed ...


2

Fundamentally it is that the $1/N!$ for the classical system only correctly compensates for overcounting of indistinguishable states if the particles are always in different states. For a system of Bosons at low temperature, where it is quite likely that many particles are in the same state, this breaks down. For a very understandable introduction to this ...



Only top voted, non community-wiki answers of a minimum length are eligible