Recent content by Gabriel Maia

Yes, know. But as I said, I'm having trouble with the physics underlying the mathematics and this is just description of the formula. It explains how. Not why. And my question is about why two resistors in series have, individually, a voltage lesser than the one provided by the battery. What...

First of all, thank you very much for taking some of your time to help me. Secondly, I understand the mathematics behind the voltage drop, but the physics underlying it is giving me trouble. I will separate my thought process into blocks and you tell me if anyone of the blocks is wrong, ok? -...

That does not explain the question about the resistor in series vs a single resistor.

Hi. I am having some trouble understanding what is the voltage drop in a system with resistors in series. If there is a difference of electric potential between two points in space, since electric potential is electric potential energy per charge, there is a difference in the electric...

Perhaps using the guitar example was a bad idea. I'm not interested in the particularities of the sound itself. I want to consider an ideal vibrating string that is not dumped in any way. You can see videos on youtube of a string attached to a wave driver. The length of the string never changes...

I'm not interested in the sound per se, only in how the string is vibrating. when I pluck a string only once is it always in the first harmonic? If not, what determines the harmonic the string is in? If I want to double the frequency of my note I arrive at the following equation...

My question is simply 'are all notes produced in a guitar produced by first harmonics?', but I will clarify what made me ask this question. Now, if you have a wave driver you can make several harmonics in a string by increasing the frequency of the machine. In a guitar string, however, it does...

Doing some math I found out that, in order for B_{t} = n\,E_{t}/c we must have E_{t} = T_{E}\,E_{i} B_{t} = T_{B}\,B_{i} So I believe it makes sense for the Fresnel coefficients to be different for both fields.

From the Maxwell Equations we know that there are four boundary conditions for an electromagnetic wave crossing an interface between two dielectric media. For the TE polarisation state, these conditions give us that E_{i} + E_{r} = E_{t} B_{i}\,\cos\theta_{i} - B_{r}\,\cos\theta_{r} =...

I have a problem with the phase of an electric field as it is reflected by and transmitted through a dielectric interface. At the boundary between the two media, all waves must exist simultaneously and the tangential component must be equal on both sides of the interface, right? Therefore for...

Hi. I'm reading a solution to a problem concerning a gas of photons. In the solution, the energy of the gas is given as E=2\sum_{\vec{k}} \frac{\displaystyle \epsilon_{\vec{k}}}{\displaystyle \exp[\beta\epsilon_{\vec{k}}]+1} where \epsilon_{\vec{k}} is one photon's energy. It is said then...

This is the problem I'm trying to understand: Consider two particles with spin 1 without orbital angular momentum. If they are distinguishable, from the rule of addition of angular momentum applied to spin, we'll have states of total spin j=0,1,2. If we have, however, identical particles which...

Hi. This is the problem 5.1-1 from the second edition of Callen's Thermodynamics. It says Formulate a proof that the energy minimum principle implies the entropy maximum principle. That is, show that if the entropy were not maximum at constant energy then the energy could not be minimum at...

I'm interested in an apparent inconsistency with the result for negative temperatures for a spin 1 system of N particles. The partition function of such a system is \begin{equation} Z=(1+2\cosh(\beta \,\epsilon))^{N} \end{equation} where each particle can be in one of three energy states...

Hi. I'm trying to prove that [\Omega] = \int dq \int dp \, \rho_{w}(q,p)\,\Omega_{w}(q,p) where \rho_{w}(q,p) = \frac{1}{2\pi\hbar} \int dy \, \langle q-\frac{y}{2}|\rho|q+\frac{y}{2}\rangle\,\exp(i\frac{py}{\hbar}) is the Wigner function, being \rho a density matrix. On the other hand...