# Tagged Questions

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### How is Work by a System Interpretated in the First Law?

Good evening. I've happened to be sitting down today and just couldn't wrap my head around this question which seems rather simple at first. From reading about the first law and sign conventions as it ...
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### Gough-Joule effect in rubber band

When a stretched rubber band is heated, surprisingly, its tension will increase. What is the physics behind this?! Another thing. The Entropic spring model says, for a good specimen, that the ...
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### What is internal energy?

My physics book says: The total potential energy and kinetic energy possessed by the particles that make up an object, but excludes the potential and kinetic energies of the system as a whole. I ...
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### What is the heated added and changes in internal energy? thermodynamics

A piston + cylinder initially contains 2 x 10-3 m3 of helium gas at the pressure of 1.01 x 105 Pa and with a temperature of 60'C. The gas is heated allowed to expand at a constant pressure until its ...
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### Specific heat at constant volume

Me and my friend came across this derivation is some lecture notes of our thermal physics module. We have been trying to calculate the partial differential of the internal energy but cannot get the ...
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### Show that change in internal energy equals zero for an adiabatic process with incompressible fluid

I have a problem when solving an exercise in thermodynamics. I am supposed to show that when we have an open system, where the process is adiabatic with an incompressible fluid, it follows that the ...
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### Thermodynamics and Internal Energy

I've been working on this problem for quite some time trying to figure out the most efficient way of answering it, So here goes the problem: There is a container, containing a monoatomic gas with ...
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### Internal energy and difference in volume at constant temperature

If the volume of a cylinder of a gas is decreased so that the work done on the gas is $W$ and the temperature is kept constant by taking away heat energy $H$. $\Delta U = -H + W$. Someone told me ...
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### Internal energy and photon absorption

I just wish to confirm whether my understanding is correct. I know that photon absorption/emission brings about quantised changes in electron energy levels. Photons (infrared) also interact with ...
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### Partition Function - TOTAL internal energy vs Average Energy

Given a partition function Z, the books sometimes uses the terms 'total internal energy' and 'average energy' exchangeably. It confuses me to no end. On one hand they say that Internal energy is ...
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### Is this how I find the rate of change of internal energy for filling a vessel?

If I am filling a tank with something (lets say air) and both its volume and pressure are changing with time (It's not rigid), it it safe for me to say: $$u=h-Pv$$ ...
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### Enthalpy in thermodynamics!

What does enthalpy tell us about? According to definition; it is the total heat content of a system, if it is the total heat content of a system then what is Internal Energy? Since we know, ...
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### How does the internal energy and entropy depend on mass?

I've found this thermodynamics question: Given a fluid described by the following equations: $$PV^{1/3}=aT^3 ,\quad U=3aT^3V^{2/3}, \quad S=\frac{9}{2}aT^2V^{2/3}$$ The parameter $a(n)$ ...
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### Kinetic energy and momentum conservation in an explosion?

My physics book says, "A firecracker sliding on ice has the same total momentum before and after it explodes." I understand this part. This is because of Newton's 3rd law, and no external forces. This ...
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### Where does the relation $u=h_f-RT+(c_p-R)(T-T_0)$ come from?

I'm working on a college project for a subject called Motorcycle Engineering, and in this project I'm supposed to do some reverse engineering on a MATLAB program to model the engine of the motorcycle. ...