Energy Definition and 999 Threads

Following the method by Peskin and Shroesder 11.4 Trying to calculate the vacuum energy of a fermion. If my method is correct so far the next step is to find gamma function , the formula I have for gamma fuctions doesn't match this equation. Can anyone help with the next step? Starting with the...

I am looking for help on the following: a) Given the system shown in the figure below, derive the steady flow energy equation from first principle. b) Again using first principles, show how the energy equation would change for the case when the system is unsteady. I am trying to learn this...

Both alpha and beta radiations can only travel short distances through air as they're not as penetrating as gamma radiations. How long gamma radiations with 22 MeV energy can travel in air? Is it meters, kilometers, miles, etc. Is there a difference between a lower energy gamma ray and a higher...

Hello all, I have a community college student who is deciding on his major. He is really interested in Fusion energy and wants to pursue that path. He was in the Engineering Program and now, after doing some research, believes he should be in the physics program (A.S. degree in Physics). The...

Hello, When discussing alternative sources of energy, like solar, wind, etc., we often hear that if the energy produced by these sources which is not immediately used, can be "sent" to the power plant and used later... I don't think the idea that is energy being transferred "somewhere" and...

Electron can move from lower energy level to higher energy level when it absorbs energy equal to the difference between the energy levels based on equation: ##hf = \Delta E## If the incident photon has lower energy compared to ##\Delta E##, then electron won't move to higher energy level. But...

Draw graphs showing how interaction energy depends upon the relative orientation of two dipoles if (i) p1 is parallel to r, (ii) p1 is perpendicular to r. I've done the first part and found the interaction energy as UInt = 1/(4*pi*epsilon0*r^3)*[p1.p2-3(p1.r^)(p2.r^)] which I know is correct...

The hamiltonian ´for a free falling body is $$H = \dfrac{p^2}{2m} + mgy$$ and since we are using cartesian coordinates that do not depend on time and the potential only depends on the position, we know that ##H=E##. For this hamiltonian, using the Hamilton's equations and initial conditions...

Hello folks, a recent theoretical discussion with a materials engineer has left my head spinning, this sort of thing is beyond me but I am curious if any of the clever folks on here could solve my problem. I want to find the Force and Energy applied by my Indenter within the following...

"What is a tuned mass damper" by practical engineering From 6:36 to 7:07How does the energy of the pendulum tuned mass damper (PTMD) dissipate energy back into the building? Intuitively, it seems like it's momentum or resonance, where the PTMD is in phase with the motion of the building and thus...

I know that there is a boundary condition at ##x=0## where the wave function becomes zero however why are the allowed energy levels odd i.e. ##n=1, 3, 5 ..##

I am trying to relate these equations to get the energy with respect to momentum based on particle wavelengths. I did the following: $$\lambda = h/p$$ so $$p= h/ \lambda $$ Then $$p=mv$$ and $$E=1/2mv^2$$ So $$E = pv/2 $$ But the answer was: $$E = p^2/2m $$ I don't understand how they...

Hi PF! I don't understand the sentence: on one side says the energy is preserved, and, at the end, the total energy of the system will change if ##W## or ##Q## is added: ##\Delta{U}=Q+W##. Greetings!

Is the mechanism of greenhouse gases trapping energy emitted as Infra Red radiation by the cooling ground either reflecting back a 50% of the radiated IR energy back to Earth or/and the greenhouse gas molecule becoming excited with the extra energy and essentially becoming hotter? Is it just the...

Hi, Answer given is $E_n=29.4 Joules$ Here is the question. Answer provided by the Chemistry math expert/Professor is as follows but it is different from the answer given. How is that? Compressibility is the fractional change in volume per unit increase in pressure. For each atmosphere...

According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf the big pulsed power accelerator, HERMES III, generate electron beam with peak energy at 22 MeV and average electron energy at 16 MeV and the resulting photon energy which is bremsstrahlung radiation is approximately 2 MeV...

The question seems similar to the one asked here, https://www.physicsforums.com/threads/energy-in-everetts-many-worlds-interpretation.966266/ but since there didn't seem to be an answer I am asking it again in a slightly different form. I was watching a youtube video where Sean Carroll...

As summarized.

Hello there, I was trying to solve this problem. I have no problem with part A and C. But in part B, my guidebook arrived with different answer. Can anybody point out what my mistake is? I am using the same method as the elevator motor problem which states : "A 650-kg elevator starts from rest...

Hi, If we multiply $En=-\frac{2\pi^2me^4Z^2}{ n^2h^2} $by $\frac{1}{(4\pi\epsilon_0)^2},$ it is the formula of electron energy in nth Bohr’s orbit. Why we should multiply it by $\frac{1}{ (4\pi\epsilon_0)^2}$ a Coulomb's constant in electrostatic force? Where m=mass of electron, e= charge...

This confusion has lingered in the back of my mind for years now, would be good for me to finally get a grasp on this. Say I have an object currently at rest, and I use energy X to accelerate it to speed v. According to the standard formula, it now has a kinetic energy 1/2mv^2. Now I use the...

Hi, I have been reading a few literature regarding excess Helmholtz energy and I encountered this definition from the paper of Wong and Sandler (apparently, from the mixing rule used in a EOS): In particular, the ones in the red boxes. How did these equations come into being? I tried to look...

Here are the results from the python code: Odd results: Even results: I tried to solve for energy using the equation: I substituted the value for a as 4, as in the code the limit goes from -a to a, rather then 0 to a, and hence in the code a = 2, but for the equation it would equal to 4...

This problem got me kinda confused since I cannot really understand the question... who tells me how the energy dissipated in this case? Has it all transformed into heat to cause the coalesce of the two particles, or ar the two particles now merged together still traveling with a certain amount...

I'm currently taking a course where we are working to teach older physics concepts and combine them with calculus. I was assigned to work on teaching a unit about energy; for the most part, it stays relatively consistent and can be solved algebraically. Another topic in this unit is Potential...

Okay For a this is what I did. a. I'm confused about B. I understand that it has something to do with the Conservation of Mechanical Energy, but I don't exactly know what to do.

Hello, I think the only energy involved is kinetic energy. So I subtract to get the difference between two stages to find the energy cost by explosion. (0.5*9.6*14.6^2)-(0.5*0.2*2.4^2)=1022.59J However the system said that this answer is wrong, So I wondered where did I make a mistake?

Hi and thanks for taking the time to read my question. So, if i take an element and place it on top of another element and heat it, will the heat energy pass through the first and charge the other or it'll melt both elements? Thanks!

Hi all- Im new. Had a weird thought and when researched I only found the answer of bc that’s how we observe it. question. Why does energy travel in waves? Bc that’s how we see it? can anyone explain to me why energy moves in waves and not a straight line? Thanks to all who help me rid...

For an ionic lattice, the contribution to the electric potential energy from a single ion will be ##U_i = \sum_{j\neq i} U_{ij}##, which can be expressed as$$\begin{align*}U_i &= -6 \left( \frac{z_+ z_- e^2}{4\pi \varepsilon_0 r_0} \right) + 12 \left( \frac{z_+ z_- e^2}{4\pi \varepsilon_0...

I = Icm + mr^2 I = 0.5 mr^2 + mr^2 I= 3/2 mr^2 By COE, mgh = 0.5(3/2 mr^2)(w^2) g(2r) = 3/4(r^2)(w^2) 8g/3 = rw^2 = v^2 / r v = sqrt( 8gr/3) v=0.511m/s ans: v=0.79m/s

Hello there, I have heard countless times about the word energy, but I still don't know what exactly an energy is. Like for example, we know the definition of a physical quantity called velocity which by definition is change in displacement (so we can easily describe what a velocity is). We...

I do not really know the relationship between potential energy and mass difference. Isn't the difference in mass of protons and neutrons due to their quarks? (the neutron is made of two down quarks and an up quark and the proton of two up quarks and a down quark.) Please help.

Hi, I am confused about the negative aspect of these quantities. The definition in my book for gravitational potential is: "The work done to move a unit mass from infinity to a point in a gravitational field" I understand that the work done is negative because gravity is doing the work if you...

Can you compare the energy loss of electrons and protons due to the radiation they emit? In fact, I want to know which of the two loses more energy when it emits radiation.

Don't really know what they want from me

There is a large increase in ionization energy when an electron is removed from a p orbital versus when it is removed from a s orbital (and likewise when it is removed from the valence shell and from the inner shells). Why is there a smaller increase when successive electrons are removed from...

In some models of the beginning of the universe, like for example in chaotic inflation, space would stop expanding in some points, creating Hubble volumes that could experience different spontaneous symmetry breaking, which would result in different properties, such as different physical...

Hello, I am learning about solutions of the Schrodinger equation including the term of rotational energy (i.e. L^2 /2I, in its quantized form) and I was wondering if there should be another quantum term describing vibrational states of hadrons or any other composite subatomic particle, in...

Hi, I take a big number of disks to composed a circle of a radius of 1 m, the blue curved line is in fact several very small disks: I take a big number of disks to simplify the calculations, and I take the size of the disks very small in comparison of the radius of the circle. The center A1 of...

E=hf-W where W is a work function. However we know that electrons in an atom will be excited only when radiated with photons of n*f0 discrete number of frequencies. where E=hf-W is a continuous function. Is this because energy level is continuous within a conductor? If we think of only...

I know the energy is ##\frac{q²}{ 8 \pi \epsilon_{0}}( \frac{1}{a} - \frac{1}{b})##, but I can't get this result using the second equation. What I did: ##W = \frac{1}{2} \int \rho V d \tau ## ##\rho = \frac{q}{ \frac{4}{3} \pi r³}, a < r < b ## ##V = \frac{q}{4 \pi \epsilon_{0} r}## ## W =...

Ve=0m/s Vp= 0m/s Qe/Qp= 1.60E-19 Me=9.11E-31 Mp-1.67E-27 Ive pretty much gathered all of the equations I think I need to solve the problem. I just am stuck. The last step I realize that the forces would be equal to each other so I have mp x ap = me x ae but then when I try to solve for the...

First, introduce the energy – momentum equation E² = p²c² + (m0c²)². Next, just think it in natural way. If the energy – momentum equation reflects the stationary situation, then, momentum p naturally equals to zero. Then, we got E² = 0 + (m0c²)², namely: E = m0c². It can be denoted exactly...

Continue reading...

1. The 4th line from the left, being the aqua blue line, corresponds to a wavelength of 486 nm, as blue light has a wavelength in the range 450-495 nm. 2. This is where I am having the most difficulty, I have tried to answer the question comprehensively but I am not satisfied with my answer. In...

If someone were to talk about "a non-physical energy source" would you consider that a contradiction in terms?

I learned that the energy operator is ##\hat{E} = i\hbar \frac{\partial}{\partial t} ## and the Hamiltonian is ##\hat{H} = \frac{-\hbar^2}{2m}\nabla^2+V(r,t)## If the Hamiltonian represents the total energy of the system. I expect the two should be the same. Did I misunderstand the concept of...

Hello, I am learning how to use calculus to derive the formula for kinetic energy now, I understandthe majority of the steps in how to do this, however, there is one step where I get totally lost, I will post a picture of the steps and I will circle the part where I get lost. If you see the...

I found the total work done is: ##\frac{q^2}{8\pi \varepsilon a} + \frac{q^2}{8\pi \varepsilon b} + \epsilon \int E_{1}.E_{2} dv## The third is a little troublesome i think, but i separated into threeregions, inside the "inside" shell, between both shell and outside both. Inside => ##E_{1}.E_{2}...