# All Questions

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### Derivative of a constant tensor field alng a path

I understand that the time derivative of a tensor filed $\mathbf T$ along a curve $\gamma\left(t\right)$ can be shown to be,  \frac { d\mathbf{T}}{ dt } = \left(\frac { dT^{ i } }{ dt } + V^{ k ...
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### Richter scale equation

According to Wikipedia, the equation for finding magnitude according to the Richter scale is $M_\mathrm{L} = \log_{10} A - \log_{10} A_0(\delta)$. However, it is rather ambiguous as to the effect of ...
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### Momentum operator of particle in electromagnetic field

In quantum mechanics to all observables correspond some self-adjoint operators. In absence of electromagnetic field the momentum operator is clearly $\vec{P}:=\frac{\hbar}{i}\vec{\nabla}$. However in ...
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### Is there a unit measured in kilogram seconds?

I'm trying to get a full grasp on the relationship between many of the units that are used in kinetic physics. I've found that it is possible to make a venn-diagram that shows the factors of many of ...
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### Is the harmonic oscillator potential unique in having equally spaced discrete energy levels?

I was wondering if the good old quadratic potential was the only potential with equally spaced eigenvalues. Obviously you can construct others, such as a potential that is infinite in some places and ...
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### How can a fruit be used as a battery cell?

Fresh fruits can be used as batteries for glowing bulbs, but how this is possible? I mean how can electric charges flow through fruits? Do they contain chemicals like cells?
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### is quantum indeterministic?

The question might look clear from a viewpoint of a non-physics guy but let me be more spesific. Can we say quantum leaps or waves or maybe the universe itself are completely indeterministic or do ...
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### Why do we fall down when the bicycle slows down? [duplicate]

My question is: It is easy to balance a bicycle when it is moving at a fairly high velocity, say 7 m/s or 25 km/hr. But when a bicycle slows down, it is hard to keep it upright, and the person riding ...
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### What is an intuitive explantion for the fact that the Maxwell-Boltzmann distribution of energies is independent of mass?

If you take the Maxwell-Boltzmann distribution of velocities (which depends on the mass) and substitute $v=\sqrt{\frac{2E}{m}}$ you get the distribution for the energies, which turns out to be ...
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### Amplitude of motion for a cart on an inclined plane attached to a spring

A very practical question. So, let's imagine that we have a small cart attached to a spring lying on an inclined plane. If I move my cart by 10 cm (measured as if there were a ruler lying along the ...
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### Describing Objects in the First Dimension

The "third" dimension is the one we experience day-to-day. An example of the "second" dimension is the shadow of a three-dimensional object. How do we describe the "first" dimension? What would be an ...
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### Why isn't jumping against a wall an elastic collision?

According to this calculator http://www.abecedarical.com/javascript/script_collision1d.html when low mass object hits high mass object it is reflected gaining opposite velocity almost the same as ...
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### Photoelectric Effect - How the electrons are regained?

When the photons with enough energy impinges on a photocathode, it emits electrons. Does this mean that the solid will lose all its electron at one point? If not, how come the electrons are restored?
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### Magnification of an astronomical telescope not in normal adjustment?

I am stuck on this question: A telescope consists of two thin converging lenses of focal lengths 100cm and 10cm respectively. It is used to view an object 2000cm from the objective. What is the ...
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### Wavelength of blue filtered light

Does blue filtered white light have a certain wavelength, or is this highly dependent on the filter and source of light?
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### How to prove when electron spin is perpendicular to linear momentum, orbital angular momentum can't be 0

And when they are paralleled, orbital angular momentum is 0.
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### Having trouble weighing the sun

So I gather the way you (and Vera Rubin) calculate a galaxy's mass is by measuring a star's orbital velocity $v$ and its distance $R$ from the galactic center, and then plugging them into this ...
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### What is Absorption Grating

I came across the word "absorption grating" in a review article. I googled it tried to find out what it means but couldn't. Could you explain it to me?
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### Inertial frames

I'm just starting my study of relativity, and I have a rough understanding of the connection between inertial frames, newton's laws, and galilean transformations, but I'd probably benefit more if ...
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### 1D Kinematics - Relative Motion involving non-inertial frames of reference

I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
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### What can currently be deduced about empty hyperspace?

Michio Kaku's explanation of universes in hyperspace in this youtube video gives a metaphor of our universe being the surface of a hyperspace bubble that's currently becoming larger. He also says ...
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### What do you exactly mean when you say that momentum is conserved?

I am taking for granted that when we say that something is conserved it is understood 'in its full integrity'. Energy is represented by a number (of J, or other) and is usually conserved. But ...
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### What is the difference between primary and volume currents in electromagnetism?

What is the basic difference between the two currents and how each is contributing to the magnetic field at source and the surface?
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### Accelerometer validation trace

I am attempting to validate an accelerometer. I have a triaxial accelerometer and placed it on a wheel which goes at various frequencies from 1 to 3 Hz. Am I right in thinking that I would expect the ...
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### Temperature in a Voltaic Cell

The potential difference across a voltaic cell varies with temperature. But my question is whether the voltage increases or decreases as temperature rises. According to the Nernst equation, the two ...
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### Why should any physicist know, to some degree, experimental physics?

I've been trying to design a list with reasons why a proper theoretical physicist should understand the methods and the difficulty of doing experimental physics. So far I've only thought of two ...
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### latent heat of vapourization

latent heat of vaporization of water is normally we use to calculate the heat transfer occurred at 373 Kelvin when water transit the phase to vapor. but we have curves which gives latent heat of ...
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### What is the status of Everett's Thought Equation?

Here is Hugh Everett's PhD Thesis: http://philosophyfaculty.ucsd.edu/faculty/wuthrich/PhilPhys/EverettHugh1957PhDThesis_BarrettComments.pdf On page 9 he says: "We have the task of making ...
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### What physical conditions would allow for this kind of perpetual seesaw

I'm working with a simulator(Box2D) and need to create these conditions. I have a perpetual seesaw with two objects on either side. I'd like for the following conditions to be met. The first ...
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### Why is optical orbital angular momentum (OAM) called “topological charge”?

The terminology "topological charge" is frequent in lots of research papers related to optical vortex or optical OAM, it is used to represent the optical OAM. Why? How to comprehend it?
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### Voltage across an inductor contradicts Lenz's law?

Imagine a simple circuit consisting of an alternating current source connected to an inductor. Assume they are connected in the following fashion: AC source - terminal A - Inductor - terminal B - AC ...
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The adiabatic approximation for solid state systems is rather radical. I was wondering in which cases it breaks down. As it is based on the idea of the nuclii being much heavier than the electrons I ...
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### What is the relationship between radation intensity and count rate?

If you know that the radioactive source is, for example, Cesium-137, is it possible to extrapolate a relationship between the count rate and radiation intensity? If it is not possible, what is the ...
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### Are the implications of an infinite universe necessarily so unsettling

I have often heard it said (by professional cosmologists) that if the universe is infinite, then there necessarily exist infinitely many copies of me repeated throughout. The reasoning seems to be ...
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### WHY does the “order” of a differential equation = number of “energy storage” elements in a system?

OK. in all engineering courses there comes a point when they introduce you to systems theory and modeling of systems (for eg. via the impulse response) and then the Laplace transform. The modern ...
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### Computationally solving bodies that push and pull

Is there a way to find a solution for the positions (as a function of time) of multiple free bodies that push and pull on each other? Say for instance I have a collection of cells which can ...
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### What are the thermal properties of a “perfectly rigid” container?

can a "perfectly rigid" container be a diathermal boundary? I checked the wikipedia article for heat and read: Kinetic theory explains transfers of energy as heat as macroscopic manifestations of ...
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### How can blackbody radition be explained by quantization?

I don't understand why quantization makes a peak on the blackbody radiation curve (so there is no UV catastrophe) and the relationship between that peak and quantization concept. When the blackbody ...
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### Does it make sense to continue searching for dark matter on Earth?

The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of ...
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### How the number of charges (colors) and the number of photons (gluons) is connected?

This question is a continuation of "Can a third type of electrical charge exist?" and specifically this comment. I know the common knowledge that there is 1 kind of electric charge and thus 1 kind of ...
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### Can a human size object move so fast that it cease to be observable?

In many anime, comics, movies, etc, we see a lot of super human beings moving and fighting at such high speeds that a regular human being cannot see that they are fighting or moving pass by. In ...
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### How do electrons interact if one of them had just exited the two slits of the double-slit experiment?

Consider the following experiment: a double-slit set-up for firing electrons one at a time. Let's now add a second electron (orange), which is fired parallel to the first one, but in the opposite ...
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### Good introductory papers and books on laser physics and pulsed lasers

I am looking for good introductory papers and/or books on the principles of lasers. In particular, I am interested in pulsed laser technology. I understand that Gould, R. Gordon (1959). "The ...
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### Third principle of Nernst. Is this expression fulfilling it? [on hold]

That is what I tried, but it does not convince me. How could I treat this problem?
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### Thermodynamic potentials: Demonstration [on hold]

I must prove whether the statement on bold is true or wrong. Under it there is what I tried, but it does not convince me. I use one maxwell relationship on the latest line. And I take advantage of ...
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### What does it mean to “convert energy into time”?

In a recent article about creating electron-positron pairs by colliding photons in a laboratory, Andrei Seryi, director of the John Adams Institute at Oxford University, was quoted to said: It's ...
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### Conservation of energy in different reference frame

Consider a rollercoaster that goes down a slope: At the higher level it has speed $v_0$, then it goes down a slope and at the end it has speed $v_0 + \Delta v$. The carriage is not powered and has ...
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### Potential due to charge over infinite grounded plane conductor using the method of images

I am reading section 3.2.1 of Griffiths 3ed which explains how to calculate potential using first uniqueness theorem. Griffiths/3.2.1 Griffiths/First Uniqeness theorem (Its corollary actually) ...