# All Questions

1answer
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### Kinetic energy of a gas molecule

I am working through the derivation of the equation $$pV=\frac13mNC_{rms}^2,$$ but relating to this formula my textbook states that the kinetic energy of an average molecule of gas is given by ...
1answer
230 views

### Non Adiabatic Coupling Term in Born Oppenheimer Approximation

I am attaching a section from a text book (Conical Intersections Electronic Structure, dynamics and spectroscopy: David R Yarkony & Horst Koppel). Here I am not understanding the so called 'Non ...
1answer
71 views

### does space-time expansion affect on fundamental particle? [duplicate]

does space-time expansion affect on fundamental particle or point particle?
1answer
61 views

### modern physics :emission spectrum [closed]

If in a hydrogen atom all possible transactions take place. The ratio of maximum frequency to minimum frequency is 135/7.what is the principal quantum number of excited state. The max frequency case ...
1answer
64 views

### What kind of research will go in nuclear fusion power once the commercial power plant is designed and implemented? [closed]

once the commercial nuclear power plant is built for electricity production , after this what kind of research does scientists do in nuclear fusion power. Why I am asking this question is ITER is ...
1answer
94 views

### Thermal Physics, Specific Question [closed]

Question: The melting point of copper is 1080 degrees Celsius and its heat of fusion is 200 kJ/kg. If a copper coin at this temperature is completely melted by the absorption of 2000 J of heat, what ...
1answer
126 views

### Earth's magnetic field

I'm dealing with a problem here. Today my professor asked us a question : How should a metallic wire move in Earth's magnetic field such that she gets maximum potential difference in it's ends: a) ...
1answer
117 views

### Red shift/blue shift: how would it appear to a fast-moving observer?

I've read sci-fi stories in which a spaceship crew, moving at some significant fraction of 'c', observes stars ahead as bluer, stars behind as redder, stars to port and starboard as...well, you get ...
2answers
233 views

### Bose Einstein condensates and gravity

Are Bose Einstein condensates affected by gravitational attraction ? In sufficient quantity, do Bose Einstein condensates exert a gravitational force ?
1answer
48 views

### electrostatics particle charging

When ash particles are charged negatively ( corona charging, ionization, tribo electric ) and then collected on to the fabric; particles arrange themselves in porous dendritic structure whereas ...
1answer
98 views

### About Hilbert and Physics [duplicate]

Was one of Hilbert questions regarding physics to make an axiomatic foundation for physics? Regardless of Godels work could some Physics principles that are 'basic' and 'presently verifiable' be ...
1answer
95 views

### Question about the Klein Paradox

I am trying to understand some points about the paradox, what I am doing is solving the for the step potential $$V = V_0 ~\theta(z)$$ I have two solutions $$\Phi_I = e^{ik_1 z} + r e^{-ik_1 z}$$ ...
1answer
45 views

### Is it possible to more cloud-layers go to different ways on the sky

Sometime when I see the sky I see that the cloud-layers go to different ways. But how is it possible?
1answer
277 views

### Bullet hits block. Show that linear momentum is not conserved [closed]

"..." First, we will familiarize us with a collision between a homogeneous beam of length, $L$, mass $M$ attached with a frictionless hinge in point $O$ at one of the endpoints of the beam. The ...
1answer
55 views

### Estimating quantum efficiency of gated avalanche photodiode

I have a photon counting system that uses a gated avalanche diode to detect single photons. The repetition frequency of the gates is $f_1$ and the temporal gate width is $\tau_1$ (so the duty cycle is ...
1answer
382 views

### Charge Distribution On Hollow Sphere

Say we have a hollow conducting sphere (with some finite thickness). If this object has an excess charge amounting to +Q coulomb, and there is no extra electric field in the surroundings (due to ...
1answer
257 views

The differential cross section of Rutherford scattering blows as $\theta\rightarrow 0$. People express this fact as "The Coulombic potential is of long range". But I am seeing the opposite: $\theta ... 1answer 82 views ### Pendulum Confusion This text in my book is pretty confusing:With my emphasis A simple pendulum is a heavy point mass (bob) suspended from a rigid support by a massless and inextensible string. This is an ideal case ... 2answers 128 views ### When solving kinematics questions, how to find time in air? I was trying to help a friend with this question: A ball is shot horizontally off a cliff. What would happen to the horizontal distance it travels if the acceleration due to gravity were doubled ... 1answer 40 views ### Probablilites for wave function collapse From what I understand, superposition is when two states exist in all of their possible forms simultaneously until the moment of wave function collapse, when they essentially reduce into a single ... 1answer 854 views ### Truck moving uphill, object suspended from ceiling, determine acceleration [closed] A truck is moving with constant acceleration$a$up a hill that makes and angle$\phi$with the horizontal. An object of mass$m$is suspended from the ceiling of the truck by a light cord. If the ... 1answer 75 views ### How to integrate two-electron interaction in He? (variational method) A probe wavefunction in the variational method is $$\psi(r_1, r_2) =\frac{\alpha^6}{\pi^2}e^{-\alpha(r_1+r_2)}$$. In$\left<\psi \right|H\left|\psi\right>$with $$H = \frac{p_1^2+p_2^2}{2m} - ... 1answer 315 views ### How hot does the upstairs need to be before it will heat the basement through convection? During the winter we keep the basement door closed so that the cold air from upstairs won't flow into the basement. Then we heat the basement and the upstairs gets heated partially by conduction ... 2answers 145 views ### Spin-Position Coupling/Interaction Firstly, is there a general procedure/algorithm for attacking Hamiltonians having spin-position coupling, e.g.,$$\frac{\mathbf{\sigma_1}\cdot\mathbf{\sigma_2}}{|\mathbf{r_1}-\mathbf{r_2}|}$$I do ... 2answers 214 views ### Can the Lorentz force stabilize the Hydrogen atom? I've recently been working on relative equilibria for some systems of particles. (ie. studying equilibrium solutions in a rotating frame. Saturn's rings for example.) This has evolved into some ... 2answers 331 views ### Information or Matter or Energy Which one is the most fundamental of the universe? What it is made of? Physicists are searching for unique and fundamental form. The question is , information is more fundamental than energy ? ... 1answer 493 views ### What does 1/k represent regarding Newtons Law of Cooling? What does 1/k represent regarding Newtons Law of Cooling? I know k represents the cooling constant. I think the inverse of k is the time taken for the liquid to cool from its maximum temperture to ... 1answer 292 views ### Does a photon travel through space exactly at the speed of light? In practice, given that in the vacuum of the universe is not perfectly empty, does the photon actually reach exactly c? Is it even possible? If it travels at exactly c, then from the photon ... 1answer 124 views ### A simple question about special relativity [closed] Assume that the table moves with the velocity \vec{v} = v\hat{i}. For the observer at x=0, the event at (ct',x')=(0,k) is observed at (t,x)=(k\gamma\beta, k\gamma) using Lorentz's ... 2answers 131 views ### Magnetic field resistance material: are there any? [duplicate] I was wondering with a question for a quite long time, thought to ask here. I need to know is there any material or element which can block magnetic field? I mean I am searching for such material or ... 1answer 59 views ### Doing a spring experiment, and need to find the stretch required I'm doing an experiment where I have to calculate the stretch of a spring needed for it to launch itself into a trashcan located some distance away. The spring is located on the edge of a ramp that is ... 1answer 53 views ### Extending a solution for \left(H_\text{osc} + \delta^{(3)}(\vec r) \frac{\partial}{\partial r} r \right) \Psi(\vec r) to Gaussian potentials I am a undergrad and currently trying to understand and use the following paper: Th. Busch u. a. Two Cold Atoms in a Harmonic Trap. 1997. URL: ... 1answer 207 views ### Capillary in a slanted tube with a bend So I've read a question on here about Capillary action in a slanted tube, but my question goes a little further. Firstly though, could someone explain to me what is meant by the only answer to that ... 1answer 190 views ### Magnetic Induction - How would different coil configurations affect the outcome? This is a branch question (from this question) related to magnetic induction: These deal with how different configurations of coiled layers might affect the outcome: If one were to bundle multiple ... 1answer 3k views ### Find the tension and angle from a vertical of a rope hooked up to an object Below is the homework problem I am working on: A 18.3-kg object hangs in equilibrium at the end of a rope (taken as massless) while a wind pushes the object with a 63.9-N horizontal force. Find ... 1answer 47 views ### Compute the minimal distance between two points in movement There are two points, A and B that move according to these laws:$$ \vec{x_a}= 20 -10 t  \vec{x_b}= -15 +15 t $$A moves along the x axis, B along the y axis. I have to compute the ... 1answer 1k views ### Landau Levels and Magnetic length I am looking into Landau Levels and keep coming across a magnetic length defined as follows for a 2D system: l_B=\sqrt{\frac{\hbar c}{e B}} I have seen numerous sources say this is: l_B\approx ... 1answer 145 views ### Balancing stick on hand - inverted pendulum motion How do I calculate the velocity and acceleration of a stick that is vertically on my hand? How fast and far do I need to move my hand from side to side to keep balancing the stick? Assuming that we ... 2answers 74 views ### Would it be possible to measure the change of entropy of a system? why? To be more specific, what I mean is to measure it in a experiment. And if the answer is no, I want to know if it is principally impossible, or just impossible due to the technic limitation of our ... 1answer 73 views ### How to define the dilatation rate (strain) between two particles knowing the instantaneous positions and velocities? Provided that I have the instantaneous positions and velocities of two particles that can separate in 3D with respect to time. I would like to characterize the change in length. What could be a good ... 1answer 85 views ### Equality of masses of particle and antiparticle Usually we say that equality of masses of particle and antiparticle follows from CPT-theorem. But do we need it for showing this equality? The first method to show that is following. The equation ... 1answer 92 views ### Angular Momentum in Quantum mechanics In Gasiorowicz's Quantum Physics, we determined the relation:$$L_z | l,m\rangle= \hbar m | l,m \rangle$$I would like to determine: \langle l,m_1 | L_x | l,m_2 \rangle I thought about expressing ... 3answers 537 views ### What is the difference between these two Feynman diagrams? In which direction is time flowing and what reactions do they represent? EDIT for Gigi (I could not add a comment to your answer): 1) Do Feynman diagrams by definition only show fundamental ... 2answers 516 views ### Relation between pressure and particle displacement in an acoustic wave Consider an acoustic wave in some medium, expressed as particle displacement:$$s(t,x) = e^{j(-\omega t + kx)}$$I understand that pressure must be at its maximum when the particle displacement is ... 1answer 166 views ### Application of Displacement Current I'm reasonably happy with the derivation and results of displacement current, however, I'd like to be aware of a few practical applications of this idea. So far, the only one I'm aware of is when ... 3answers 116 views ### Which particles can go right through the atom? Can elementary particles (like the electron, photon, or neutrino ) go through an atom (not the nucleus)? 1answer 49 views ### Does bragg diffraction affect intensity of transmitted light? Is it possible to measure the plane spacing in a crystal by measuring the angle at which transmitted light intensity dips? 1answer 69 views ### Virgo SuperCluster and space time Is the Virgo Supercluster affected at all by the expansion of space? What about the larger filament that Virgo resides in?I don't quite understand how gravity affects space time locally in groups of ... 1answer 380 views ### Moment of inertia of a hollow sphere wrt the centre? I've been trying to compute the moment of inertia of a uniform hollow sphere (thin walled) wrt the centre, but I'm not quite sure what was wrong with my initial attempt (I've come to the correct ... 2answers 591 views ### Isobaric expansion work, W = p(V2-V1) [closed] Isobaric process, so$W = p\Delta V$according to my book. We have 10 kg of saturated steam at$x = 0.9$, P = 200 kPa. We add work at a rate of$700 W\$ and we're interested in the time it takes. We ...

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