# All Questions

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### Are there any naturally occurring examples of photons without mass?

I read that a photon is said to have zero mass at zero velocity. Does this mean that they only exist in a state of probability until observed && interacting with some system? And then when ...
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### Do transformers lose energy?

EDIT: The title should rather be how/why transformers lose energy My idea of a transformer is that it is composed of two separate wire windings around some metal core. The purpose is to ...
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### Fractional quantum Hall effect [duplicate]

Can someone explain the fractional quantum Hall effect in layman's terms, I'm having some difficulty understanding it?
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### How do magnetic field lines cancel outside of a solenoid?

Please explain me briefly, how magnetic field lines cancel outside solenoid? There is only one wire wrapping it and therefore only one direction of current so how can magnetic field cancel out? How ...
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### Field theory for a finite temperature normal fluid

Can normal-fluid (not superfluid) hydrodynamics be derived from some classical field theory? Here I mean conservation (continuity) equations for mass (density), momentum, and energy (entropy, ...
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### What is the physical reason that the undamped driven oscillator has mean power zero?

The instantaneous power absorbed by an undamped driven oscillator is given by:$$\mathbf{P} =-\omega\dfrac{F_o/m}{{\omega_0}^2 -{\omega}^2} F_0 \sin{\omega t}\cos{\omega t}$$. But my book says the mean ...
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### Does nucleus itself has its own motion?

We know that electron(s) is(are) moving around the nucleus, that consists of protons and neutrons. But does nucleus itself has its own motion, its own momentum, or the nucleus is stationary? Now, is ...
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### What happens to half of the energy in a circuit with a capacitor?

For a simple circuit with a battery supplying a voltage V to a capacitor, let us assume that the charge on the capacitor is Q. Now, the work done by the battery or the energy supplied is given by the ...
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### Why are L4 and L5 Lagrange points stable as points and not part of a circle?

I read this Phys.SE thread which is similar Why are L4 and L5 lagrangian points stable? but I did not want to necro that thread. It seems that most discussions of a three body problem are presented ...
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### Work done by moving up an inclined plane

Suppose an object is pushed up a smooth inclined plane from ground level to a point h above the ground with force F. The angle of inclination is A. How much work is done? To push an object up a ...
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### How to determine whether a nuclear transition would be electric octupole, or hexadecapole?

The transition from one nuclear state to another is classified as quadrupole/octupole, etc, depending on the units on angular momentum transferred. But depending on the angular momentum of the two ...
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### Application of Coulomb's Law

I've just finished reading a section in a book on Coulomb's Law. I'm trying to practice the math a bit and came up with the following: Suppose you have two charges, -5uC ($q_1$) and 7nC ($q_2$). ...
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### Why mirrors form image and others don't?

In the case of mirror, I understand how a image is formed, If I replace plane mirror by wood or some other opaque material in the above image and position of object(bottle) and eye remain the same , ...
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### How to determine which object is moving relativistically?

Apologies in advance if I've overlooked some obvious point. In relativity, I know that there is no way to know if Object A or Object B is moving relative to the other. Each would see themselves as ...
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### Hot air ballon and a sandbag moving at constant velocity

Suppose you are in a hot air balloon with a sandbag that has a certain mass. The hot air balloon is moving upwards at a constant velocity of $15$ $m$.$s^{-1}$. If you throw the sandbag out of the hot ...
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### EM waves in conductors

On a recent test in my E&M class, we derived what happens to an EM wave propogating in a conductor of conductivity $\sigma$, but I'm having trouble understanding the results. We started from the ...
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### About a recent experiment which claims reality doesn't exist until we measure it?

Reality doesn't exist until we measure it, Quantum Experiment confirms. Is this one more experiment which is the victim of how news generally hypes stuff like this? This is a section from the ...
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### Is a string taut if the tension is zero?

I'm studying vertical circles and a particle on a string will remain in motion as long as the string is taut. However, what if there is 0 tension in the string? Is it still technically taut?
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### Is sunlight like a spotlight? [closed]

It is believed that if earth would have no atmosphere then the sunlight would fall on earth like a spot light. According to this fact the sunlight on moon must fall like a spot light. Does it? Then ...
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If we have one particle we first look at an orthonormal basis of the one-particle Hilbert space $|n\rangle$. Here $n$ is the abbreviation for a compete set of quantum numbers, for example $n = ... 2answers 108 views ### Why does the ball lose contact if it has velocity great or less than$\sqrt{rg}$, while moving over a smooth sphere of radius$r$? Let a ball of mass$m$is given a velocity over the the top of a smooth sphere of radius$r$. The equation of motion at the topmost point will be $$mg - N = m\dfrac{v^2}{r}.$$ As$v$increases,$N... 1answer 39 views ### When align the neutron's magnetic dipole moment, does moving neutron radiates? Was performed an experiment in the past, where neutrons pass a magnetic field and their magnetic dipole moment get aligned? Was measured an electromagnetic radiation during the experiment? 1answer 70 views ### Is a zero-energy universe necessarily also a zero-information universe? The universe needs to be near zero energy to not crumple in on itself. Under the same logic, does it also need to have near zero information content to prevent the passage of time from burning it to ... 2answers 112 views ### Lorentz force Law I want to ask a fundamental question about Lorentz force equation. Why is it important to incorporate both electric and magnetic forces into one single expression? I know magnetism is electricity's ... 1answer 84 views ### Can someone explain what's the difference between all these terms in “Simple Words” with their “applications”? [closed] I'm very confused between all these terms. Can someone explain what's the difference between Classical Mechanics, Relativistic Mechanics, Quantum Mechanics, Quantum Field Theory, ... 4answers 218 views ### Ohmic Heating in Wires please could someone tell me why Ohmic losses are always referred to asI^2 R$losses? Here is my problem. If the power coming from a power station is fixed then you can either deliver this power as ... 1answer 27 views ### Adjoints in occupation number representation I am having some trouble understanding how to compute things in occupation number representation. I believe my problem is only implicitly dealt with in the notes I have read. A simple example should ... 4answers 931 views ### Why do like charges repel and opposite charges attract? [duplicate] Why do like charges repel and opposite charges attract? 1answer 118 views ### What physical properties can we measure most accurately? As far as I am aware, frequency is the most accurate physical property we can currently measure. This has led us to very high standards of experimental verification of e.g QED predictions and the CMB ... 3answers 264 views ### How exactly does wave theory of light fail to explain blackbody radiation? [duplicate] I don't really understand the reason why wave theory of light fails to explain the blackbody radiation. My textbook says the Planck's quantum theory explains blackbody radiation. It says "If we ... 2answers 61 views ### It's All About Earthquake! [closed] All the following informations i've got are from a book.(i want to check that whether the informations are correct or not,that book isnt a science book though) There is a limit to which earth can ... 1answer 37 views ### What is meant by “method of approximate numerical method” or “method of digital computer” for solving the differential equation of resistive force? I was reading "motion against resistive forces" in Newtonian Mechanics by A.P. French; here is the excerpt: [...] In general, the resistive force$\mathbf{R}$is is a function of speed, so that ... 1answer 51 views ### Quantum Entanglement Particle Properties I have background in static/dynamic/thermodynamic physic. I am reading on quantum physics and quantum entanglement. Me and some of my colleagues were wondering on the properties that are shared ... 3answers 183 views ### Question on normal force and static friction [closed] Why is this statement false: If the normal force on an object increases, the static friction must increase? Thank you! Is it because they did not state what normal force is referring to? 1answer 51 views ### Is it possible to create helium atoms by bombarding heavy water with neutrons? If heavy water is bombarded by neutrons is it possible that any of the deuterium atoms can capture neutrons and transmute to helium atoms? I suspect the more probable event would be knocking protons ... 2answers 179 views ### Dimensional Analysis Question [closed] First of, I would like to say that I have tried this question, and have my answer as well, just not sure such a method of obtaining the answer is valid or not, therefore trying to look for help here. ... 1answer 129 views ### Helium balloon stays on the floor So yesterday I came back home with a buoyant helium balloon (no comment, and before you ask, it's blue) and I left it in the house. Obviously, it rose to the ceiling. This morning I woke up to a ... 2answers 1k views ### Calculating the energy supplied by a battery If you wanted to calculate the energy supplied by a battery in time$t$you would use$E=VIt$where$I$is the current through the battery. If the internal resistance is$r$we could also use ... 2answers 88 views ### Frames of reference and why are they different Here is a quote from "The Elegant Universe" by Brian Greene. Imagine two countries that have been at war are sitting down to sign a treaty ending hostilities while traveling aboard a train that is ... 1answer 566 views ### Question about ohmic conductors I'm having some trouble understanding Ohm's law. My trouble is with the different ways it is described when referring to ohmic and non-ohmic conductors. If someone can answer this question I think it ... 3answers 147 views ### Is it possible that the charged sphere can lose mass by adding electron? While studying Electrostatics, I was wondering about whether a charged sphere gains or loses mass while just adding electrons? If it is possible then the negatively charged sphere will have more mass ... 1answer 65 views ### Why water expands when freezes? [duplicate] I'm sure this is for most of you a basic question, but it really puzzles me: How it is that, even though all materials expand as they get warmer, and contract (maybe these are not the correct terms) ... 1answer 373 views ### Pendulum on the moon, (Highschool) A simple pendulum used as a clock, set with the correct time at earth, was sent to moon, it was noticed that it is late 36mins for each hour on earth. Calculate the ratio between acceleration of ... 2answers 90 views ### Energy transitions of 12.1eV electron? Here is part of the energy level diagram of hydrogen: n=4 --> -0.85eV n=3 --> -1.50eV n=2 --> -3.40eV n=1 --> -13.6eV When an electron of energy 12.1eV collides with this ... 3answers 172 views ### Since the gravitational force is only attractive, why does matter not just concentrate into a small sphere? This doubt has been wandering in my head for a long time. The gravitational force is only attractive force not a repulsive force. Since gravitational force is only attractive force, why not the ... 1answer 58 views ### is it necessarily true that the partition function$Z$(with degeneracies)$ =1\$?

The partition function with degnerate energies is $$\text{Z}=\sum _ig_ie^{{-E_i}/{k_BT}}.$$ Because the partition function Z is defined as the normalisation constant, does Z always = 1?
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### Will going up with a larger diameter ensure a higher water pressure in the distribution pipes? [closed]

Have a look at the drawing below describing a sample situation: a water tank a 1'' diameter pipe bringing the water down, inside the ground, arriving near the house in the house, 2 x 0.5'' diameter ...
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### Charging a capacitor using a capacitor?

I recently did an experiment using a fully charged capacitor (assumed) and charged a separate capacitor through fixed resistor. We measured the potential difference of the capacitor being charged. We ...