# All Questions

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### Is there a Ramond vacuum for real fermions?

When studying the CFT of a complex fermion $\Psi$ we know that if it's periodic, ie if $$\Psi(\sigma_1+2\pi,\sigma_2)=\Psi(\sigma_1,\sigma_2)$$ then there is a doubly degenerate Ramond vacuum which I ...
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### Different kinds of energies in the form of $\frac{a_1a_2^2}{2}$

It seems to me that the energy of some kind frequently takes the form $$\frac{a_1a_2^2}{2}$$ Where $a_1$ and $a_2$ are some variables. So, for example, kinetic energy has $m$ and $v$; rotational ...
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### Can we create plasma with other things except gas?

In my school book its written on how plasma is created and it is said that we can create plasma by ionizing a gas but i have heard that plasma can be created even from liquids like water and also from ...
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### Why the image is being formed at the surface?

Last week I encountered a very cool optical phenomenon. A photo was sandwiched between the two glass plate to make the paperweight. The cool part is the picture seems to have been pasted on the top ...
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### What causes “stringy” melted cheese (and similar behavior in other materials)?

I was wondering about this. What is the physics underlying the "stringy" consistency of melted cheese? That is, when the melted cheese is hot, and it is pulled apart, it forms strings of cheese. This ...
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### Speed, weight and force

If a road roller of weight $W$ is rolling on the road at the speed of $X\,\mathrm{kmph}$, how much force does it apply on the surface of the road (considering a sampled surface of the same size as ...
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### How do you become a theoretical physicist? [on hold]

Is there a specific subject at university called "theoretical physics" or do you get a PhD in Physics and then if your job involves theory you are considered a theoretical physicist?
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### D-T fusion reaction releases 17.6 MeV of energy

How to show that the D-T fusion reaction releases 17.6 MeV of energy ? I am only getting it as a fact but how can I prove it ?
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### Which units are affected if we double the unit of length/velocity or force? [on hold]

If the unit of length: $m$, velocity: $v$, and force: $N$ is doubled, which of the following options is correct? (changes in other unit) unit of time is doubled unit of mass is doubled unit of ...
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### Why U235 over U238?

There are 3 isotopes of uranium that can be found in nature[1]: U234, U235 and U238. For a chain reaction to last there must be a high amount of neutrons contents and by comparison, U238 contains 92 ...
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### is it possible to measure mains induced current flowing from my body to ground?

I can measure a voltage that is induced on my body via an electromagnetic field from a 50hz ac source, and would like to know if it's possible to measure the induced current on my body, if any, when ...
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### Non Combustion Atmospheric Propulsion [on hold]

Is it possible? With electric motors set aside, what are the viable options for propulsion?
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### Motivation for isospin

I am having trouble understanding the point of isospin. Why do we need isospin? The rationalization that protons and neutrons are similar doesn't make sense to me.
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### Why 'free energy' can contain different amount of information in different settings, and what's their connection to phase transition?

I have seen 'free energy' arising from several contexts in very different forms, and each contains different amount of information (as a number, 1D function, 2D surface, etc). For example free ...
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### Photons and EM Fields

I started learning the basic ideas of QFT in an intuitive manner ( withouth any math, only with mental videos and pictures ) some days ago, and i'm finding it completely beautiful [ the idea of ...
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### How to explain the momentum exchange of two solid particles collision at molecular scale?

Here is my question: assume two solid sphere collided to each other in vacuum, at macroscopic, it can be explain by Newton's law. But at molecular scale, does the surface atoms touch to each other or ...
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### How can I rearrange an equation to find a gradient for a capacitor?

If I plot R on the x axis and T on the y axis to give a straight line graph, and I am given that $V$ = $V_0$ * e^(-t/RC) then how can I prove that the gradient of the graph is equivalent to $C$ * ln3, ...
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### What does an increased time constant of a capacitor do?

If a capacitor is being charged to any voltage, what effect would increasing the time constant have on it and if a graph of Charge Q/Time T was plotted to give a positive decreasing gradient, how ...
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### What happens to magnetic $B$-field in a superconductor in the Bean model?

In the Bean model, as we start applying a magnetic field $H$ in the plane of a slab, the $B$-field inside the superconductor decreases linearly from each side, and at a sufficiently high field $H^{*}$ ...
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### Object Pushed by Multiple Forces

If we have a general object and we have multiple forces acting on it at several points. Assuming we know the center of mass, mass and moment of inertia of the object: Will the object rotate only ...
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### How can I calculate percentage uncertainty?

If the percentage uncertainty of T is the modulus of 1/($lnV_0$-$lnV$) and the precision of $V$ and also $V_0$ is +-0.01V with peak voltage at $V_0$ = 12v and the statement $V$(ln$V_0$-ln$V$) ...
For a particle trapped inside a rectangular box of side lengths $l_x$ $l_y$ and $l_z$, the energies are ...