# All Questions

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### Higher $L$ lower energy?

For multi-electron atoms, what is the physical reason behind the fact that a higher total orbital angular momentum, $L$ gives a smaller total energy, $E$?
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### Decay kinematics of Higgs boson

So I'm looking at a two-body decay question for the $h\rightarrow\gamma\gamma$ decay channel for the Higgs Boson. I am asked to find the invariant mass of the Higgs boson. I'm not too sure how to ...
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### Spatial coherence of SLED light (width of active region?)

As far as I know, super-luminescent diodes (a.k.a. SLEDs) have a very similar structure to laser diodes, except that the front faces of the active region are tilted to prevent the sort of reflections ...
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### Rogers-Ramanujan and integrable systems

I'd like to understand the underlying geometry of the Rogers-Ramanujan continued fraction from the point of view of integrable systems (ideally Toda type theories). The generating function ...
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### Relationship between fracture of solid plates and its curvature

I do some school projects about fracture of glass, my assumption is this phenomenon related to the curvature of these plates, specifically, fracture starts from the point which is having “maximum” ...
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### Motivation for usage of 4-vectors in special relativity

I understand that if one considers a 4-dimensional space-time from the outset then 4-vectors are the natural quantities to consider (as opposed to 3-vectors as in Newtonian mechanics), since the ...
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### Which way does the force due to current point

The current is towards the right. The particle with charge $-q$ is going with velocity towards the right. How does one find the force due to the current on $-q$? (The RHR doesn't do anything here). ...
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### Current scientific knowledge of antimatter [on hold]

I am currently working on a theory and need to know something. How much do scientists know about antimatter? About it's properties, charges, location in the universe, etc. If this question will ...
386 views

### Why was the Stark effect discovered much later than the Zeeman effect?

This is strange. The Zeeman effect involves the magnetic field. The Stark effect involves the electric field. In the course of classical electrodynamics, we get the impression that for many physical ...
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### Do stars remain electrically neutral? [duplicate]

How electrically neutral do stars remain through their lifetime? As an example, I could imagine processes such as coronal mass ejections leaving the Sun in a slightly charged state. Are there such ...
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### Why do $C_p$, $\alpha$ and $\kappa_T$ all approach to infinity when two phases coexist at the mean time?

My textbook (writed by Chinese) says that when two phases of a system coexist at the same time, this system's isobaric thermal capacity $C_p=T(\frac{\partial S}{\partial T})_p$, coefficient of ...
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### Question pertaining to the branching ratio of Ka0ns

I'm a little lost for part c of this question: I understand the $\mathcal{BR}$ (branching ratio) for species $i$ is $\mathcal{BR}=\Gamma_{i}/\Gamma_{T}$ (total Decay width). I know that ...
312 views

### Drag - Dimensional Analysis / Buckingham Pi

Dimensional Analysis / Buckingham Pi Theorem I'm working on dimensional analysis and I'm having trouble. Here's a problem from my book I'm working on for practice. I'm suppose to consider a small ...
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### Does the electrons in Stern-Gerlach aplliance change their energies and how?

When an electron goes thru a Stern-Gerlach appliance it changes its spin projection. Then there must be a change of energy content of the electron due to this event. But it is also known that magnetic ...
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### Finding the exponent of $\lambda$ in Wien's displacement law

I am reading this paper on a short history of the $T^4$ radiation law. In particular, on page 5, By assuming that the wavelength of radiation emitted by a molecule was a function only of its ...
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### What is the amount of Power required to maintain a flywheel at an angular velocity $\omega$ rad\sec of mass $M$ kg and Radius $R$ m? [on hold]

What is the amount of Power required to maintain a flywheel at an angular velocity W rad\sec of mass M kg and Radius R m ?
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### How do I get the maximum EMF in this problem? [on hold]

Concern is often expressed regarding the potential adverse effects of oscillating electric and magnetic fields on the human body. Consider a typical magnetic field created by mechanical ...
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### Is there an equation to calculate efficiency of an optical fiber to transmit sunlight for length of 4 m

I want to transmit sunlight over a distance of approx 4 m via optical fiber. Ideally I want to light up the whole house with sunlight. I was reading that the largest diameter for an optical fiber may ...
257 views

### Electric field in space created by intersection of spheres of charge

I am trying to calculate the electric field in space created by a body assembled by the intersection of 2 spheres. The upper sphere, its center is at $$\frac{d}{2}\mathbf{\hat{z}}$$ with radius $R$ ...
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### Blue bird physics- Angry Bird

This is a question from my assignment which is Angry Bird related. Here it is: Before designing new types of birds for the Grumpy Birds game, you are asked to first verify the design of one of ...
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### Does the human body have a measurable gravitational field?

I am researching communication other than speech or vision. The human body emits radiation in the form of heat; As the body has mass, will it have a gravitational field?
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### Heating during expansion in Joule Thomson - Mechanism?

When a real gas(like H2,He) expands through a porous plug into free space, they heat up. How? How does it get the extra energy?
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### Magnetic dipole moment aligning with external field

Is there a law governing the tendency for the magnetic dipole moment to align with an external magnetic field? If you look at the classical model of an electron orbiting a nucleus, Fleming's Left Hand ...
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### Can drag force and lift force be in the same direction in the following case?

In the attached picture, can I say that there is a lift force in the Y-direction, and a drag force too in the same Y-direction? $F_L$ proportional to $V_fx^2$ ? $F_D$ proportional to $V_py^2$ ? Is ...
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### How commutators reverse the direction of current?

I've seen this video and read this article about commutators but I still couldn't get how commutators reverse the direction of current.I would like an simple and intuitive answer.
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### Is 0.1 bar (hydrostatic pressure) equivalent to 0.1 bar vacuum pressure (absolute pressure)?

Suppose we would like to test the ability of an objec to withstand the pressure under 1 meter of whater. I would like to understand how to simulate this situation using vacuum. Is the 0.1 bar (for 1 ...
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### Simplest explanation of pendulum having a constant time period at low angles

What is the simplest explanation for the pendulum having a constant time period at low angles?
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### Thermodynamics - Change in temperature based on time

Hello Physics Stack Exchange, This is my first post on this forum, please correct me on any semantic mistakes I may make. Recently in my physics class we did a lab on Heat Capacity, where we had a ...
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### Could dark energy and particles create magnetic field? [on hold]

Could dark energy create magnetic fields or is this just quintessence theory?
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### Optimum “fur” dimensions for absorbing ultrasound at a given wavelength?

By "fur" I mean an array of bendable fibres aligned vertically on a substrate. The ultrasound hits it at an oblique angle. Is there a spacing that will provide optimum absorption? A basic thought ...
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### Pulley Advanced Problem [on hold]

How to show that M would have to be more than 8m
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### Electromagnetism question involving magnets on the ends of a metal pole

My teacher showed us a phenomenon in school involving a metal pole with two magnets on each end. The magnets are aligned so that both south poles are stuck to each end of the metal pole. This results ...
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### Invariant amplitude in QED in terms of Mandelstam variables

So I'm having a little trouble with this question: These are my workings thus far: I just can't seem to get certain terms to vanish. I have the 1/4 factor for going between $8e^4$ to $2e^4$. Is ...
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### Writing operator evolution as a quantum dynamical map

In the Heisenberg picture we have the evolution of the operator in time given by: $$A(t)=U^+A(0)U$$ I was looking into the theory of open quantum systems where we introduce the concept of a quantum ...
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### Binocular vs. monocular field of view in head-up displays

I've been reading about head-up displays in Wiki: Head-up display and understand that it works such that an image from an LCD screen (automotive) or from a cathode ray tube (aviation) is projected to ...
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### The effect of an electric field on capacitance

Decreasing the distance between the two parallel plates of a capacitor increases the amount of charge that can be held on each plate. If this is because the charges are attracted to each other and ...
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### Why don't we call the fermions in the standard model force carriers?

Maybe this is a chicken-and-egg problem, but couldn't we call all the bosons fundamental and treat the fermions as force carriers between them? EDIT: After all we never see the asymptotic states of ...
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### Does the dispertion medium affects Quantum Dots fluorescence efficiency?

I would like to use CdTe Quantum Dots to make a fluorescent coating on a transparent support. There's a link to the material here: ...
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### Pulley Advanced Equilibrium Problem [duplicate]

How to show that M would have to be more than 8m
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### Diffraction and wavelength [duplicate]

Why is it that when the slit-width is much larger compared to the wavelength of light, there is little diffraction or spreading-out of the light? And why is it that the diffraction effects are ...
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### Will the force acting be doubled? [duplicate]

If me and a man are holding a string, and I apply a force of 100N, the tension in the string would be 100N, and it would exert a 100N force on the man and an equal and opposite force of 100N on me. ...
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### Confused regarding sign convention of silvered plano convex lens

I'm totally confused while finding the sign convention of a silvered plano convex lens. I know that equivalent power of such a system can be found by adding the power of the mirror and twice the power ...
In the standard derivation of Maxwell's area construction (which can be found on page 4 of this pdf) the following equation is often written: $$G(p_1,T)=G(p_0,T)+\int^{p_1}_{p_0}Vdp$$ When the two ...