All Questions

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Confusion between TWO shear stress formulas

There are two formulas that I have encountered so far for shear stress in my Engineering class. Let S be shear stress, F be force, and A be cross sectional area: S = F/A Note: This formula is ...
460 views

What happens when you pass a current through a coil made of a ferromagnetic substance?

I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type ...
47 views

Green light in the satellite image

What could be the possible reason for the green border visible in this satellite image ? (Image source)
9 views

Shaving down length of a GRIN lens to a desired wavelength

I have a GRIN lens that collimates light from a point source at 670nm. I want to shave the thickness of the lens down to use for 530 nm. I can't find anything useful for equations online. None seem to ...
9k views

Why wet is dark?

When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks ... What is the reason for this? How does water soaking into the material ...
24 views

Do solids have translational energy?

Along with having vibrational energy, do both crystalline and amorphous solids also have translational energy? I ask because I've always understood solids to have just vibrational motion/energy. But ...
36 views

infinitesimal and infinity [on hold]

In differentiation and integration we use infinitesimal to evaluate derivative and integral, talking about infinitesimal first this is the no. that we actually can't say how small it is still we are ...
159 views

Magnetic Energy Density Equations

I have a plasma with a magnetic field through it and I want to know the magnetic energy within the plasma. I have the simple equation $U=\frac{B^2}{\mu}$ for the energy density. But my question is ...
38 views

We can move with speed of light [on hold]

We all know de-broglie equation $λ = \frac h {mv}$ but let us take it a little further. Let $λ$ be the wavelength associated to an object with mass $m$, $v$ its velocity because of its energy $E_G$ ...
36 views

Help trying to make circuit! [on hold]

I tried to make circuit. I have battery of 9V and led light with Vf of 3.30. How can i find the cureent of circuit. Basically two wires are going from battery to led bulb making it light but can i ...
171 views

Luminance from multiple light sources

I have a LED diode: Given Luminance intensity [I] of $1.85$ cd. I want to have Luminance [B] from the light source of $75 \ {\rm cd/m^2}$. From $B=I/S$, where S is light source plane area, I get ...
23 views

What do water stains make things appear dark? [duplicate]

If a piece of grey tarmac is damp after the rain, it appears darker. If I spill water on my carpet, the damp patch is darker than the rest of the carpet. Generally speaking, a lot of things appear ...
46 views

At what wind speed does wind chill's conductive cooling exactly cancel out the compressive heating of the air?

At relatively slow wind speeds such as 15mph, wind chill drains heat from an object as it flows past, and this conductive cooling effect seems to increase as the wind speed increases. However, at very ...
35 views

If a body slides down a frictionless inclined plane what will be the net normal force?

If a body(m) slides down a frictionless inclined plane (M), will the net normal force between the ground and the inclined plane be (M+m)g ? I feel it should be less than (M+m)g. This is because one ...
39 views

Why bremsstrahlung occurs only with the nuclei? Why not with the electrons?

In many books I read that bremsstrahlung effect (for e+) only occur when the electron goes near the atomic nuclei. Why is not possible when cross near an atomic electron? Thanks,
10k views

Relationship between amplitude and frequency of a wave

What is the relationship between amplitude and frequency of a wave? Some say there isn't any relationship, some say that there is, but from their answers the relationship is still unclear.
104 views

Nobel Prize challenge: Could neutrinos be used for quantum information processing?

We know that two scientists, Takaaki Kajita and Arthur B. McDonald, working on Neutrinos have just been awarded the 2015 Nobel Prize in Physics. My question as a Nobel Prize Challenge Question is: ...
1k views

Liquid nitrogen and liquid helium

In cryogenics, liquid nitrogen and liquid helium are often used as coolants. Other than their low boiling point of 77K and 4.2K respectively, what properties make them suitable as coolants? Are there ...
156 views

Is work done by a pseudo force?

If a body is viewed from the frame of another body which is itself accelerating, will work be done by the pseudo force acting on the first body in the frame of second body ( provided the first body ...
414 views

Hamiltonians, density of state, BECs

When working with Bose-Einstein condensates trapped in potentials, how can one tell what the density of state of a system of identical bosons given the Hamiltonian, $H$? (I have been told that it is ...
3 views

Attracting atmospheric positive ions to carbon nano tubes for collection

Can nano magnets built into carbon nano tubes be used to attract moving positive ions from atmosphere to increase the resultant positively charged collecting mass?
48 views

Can meters measure a distance in higher dimensions?

Consider meters as a unit of measurement. Meters can, of course, be used to express distance across a two-dimensional plane. E.g. The distance from your chair to the door is 2 meters. Meters can also ...
53 views

Timelike Boundary

I was reading in a paper (see 1st paragraph of introduction section in http://arxiv.org/pdf/1510.00709.pdf) that in AdS space, waves can reach the boundary in finite time and, since said boundary is ...
25 views

Proving the following cycle is equivalent to Carnot cycle

I want to investigate whether the following cycle I'm about to describe is equivalent to Carnot cycle or not. By equivalent I mean, giving two reservoirs($A$,$B$) with temperature $T_1$ and $T_2$ ...
37 views

Does magnetic induction produce potential across zero resistance wire?

If magnetic field is increased at a constant rate inside a zero resistance wire loop, then, according to Faraday's law , $$\varepsilon = \frac{dΦ}{dt}$$ Thus, a potential difference is produced. ...
245 views

Big Bang…or…Everywhere Stretch?

Recently I watched a minute-physics video that suggested that a better name for the beginning of time would be "Everywhere stretch" because there wasn't a space-time singularity that formed where the ...
12 views

All contour integrals in the world are zero…? [migrated]

Using Stoke's theorem, line integral of a vector gives surface integral of curl of the vector, and after that if we apply gauss' divergence theorem in that, it gives vol integral of div of curl of ...
13 views

Entangled or Separable-State measurement

This image is from a Nature paper. A question about the caption: how is Victor's data used for sorting Alice and Bob's measurements into subsets? I would really appreciate it if you could walk me ...
22 views

Why does a block 2 on a oscillating block 1 start sliding at the maximum acceleration?

A block of mass $m_{1}$ is oscillating horizontally with another block on it of mass $m_{2}$. There's friction "k" between both blocks, so the thing is why the second mass starts sliding at the ...
18 views

equilibrium state of a system in statistical mechanics

Why we consider the maximum number of micro states or complexions as equilibrium state of a macro state or a system in statistical physics?
12 views

Can Ultrasound and or Microwaves actually lock mass in place trapping it in standing wave nodes

Ultrasound Standing waves trap small particles and manipulate their velocities and direction and cause them to defy gravity. Source : https://www.youtube.com/watch?v=odJxJRAxdFU Does current physics ...
24 views

Question on Electromagnetic Induction

If a magnet is moving through a solenoid, why is there no electromotive force being induced while the magnet is at the centre of the solenoid? (Is it because emf is induced in both directions?) Can a ...
74 views

How dangerous is the radiation from a fiesta-ware plate?

I know that with a Pancake probe you can get up to 30K CPM on a small plate. I ordered a 6" red plate off ebay and measured outside the box when it came in. It registered around 200 CPM on a CDV-700 ...
39 views

Capacitors in parrallel [on hold]

There are two $20 \mu F$ capacitors in parallel that are connected in series to one $50 \mu F$ capacitor. The p.d across the parallel pair is $30 V$, what is the charge on each capacitor? The EMF of ...
120 views

Atmosphere model

Im working on project where I should simulate glider soaring. The goal is to create gliders that will look for regions with hot upwinds using evolution algorithms. That shouldn't be problem. What I ...
11 views

The Exchanged Force Pulse from reversing magnetic field increases the field strength a few hundred times [on hold]

How do we account for such a dramatic field increase just by reversing the magnetic field ? What is at work here? Richard Feynman Physicist is a source for this effect.
36 views

Does a changing magnetic field impart a force on a stationary charged particle?

Does a collapsing and re-establishing magnetic field impart a force on a stationary charged particle ? Does the charge particle get repelled and or attracted ? Does it move or spin ?
37 views

How Did the Universe Manage to “Explode”? [duplicate]

I'm taking a slightly different "look" at the Big Bang. I do not question the Big Bang's validity but there is one oddity about it I don't think I've ever seen adequately addressed. Our universe is ...
36 views

Bernoulli equation as an energy conservation equation

I don’t want to learn and apply Bernoulli's equation. It is complicated and you need to remember a lot. I instead want to apply energy conservation. But I don't always find it easy. For example, when ...
293 views
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Does the poisson bracket $\{f,g\}$ have any meaning if neither of $f$ or $g$ is the system's Hamiltonian?

Say one has a mechanical system with hamiltonian $H$, and two other arbitrary observables $f,g$. $H$ is super useful since $\{H, \cdot\} = \frac{d}{dt}$. But does $\{f,g\}$ give any useful information ...
12k views

How do electrons jump orbitals?

My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals ...
7k views

Heat and work are not the state functions of the system. Why?

Heat and work, unlike temperature, pressure, and volume, are not intrinsic properties of a system. They have meaning only as they describe the transfer of energy into or out of a system. This is ...
9k views

Why does water sometimes form bubbles when I pour it into a glass?

Sometimes when I'm filling up a container with water from the tap, bubbles will form on the top of the water. They look a little like soap sud bubbles, but there's no soap suds present. I notice, ...
46 views

What makes a lens a lens?

I am asking about the way that a convex lens works. All the lenses I have ever seen were solid glass or solid plastic. If I have a convex sheet of clear glass or of clear plastic, shaped into a ...
19 views

Tight binding on sawtooth 1D lattice

I am reading the paper "Bose condensation in flat bands" (arXiv). The authors consider a tight-binding model on the one-dimensional "sawtooth" lattice, comprised of two sites A and B in the unit cell ...
30 views

Relation of spring constant with mean radius of spring

My teacher says that spring constant depends on its radius. I tried to understand it, and checked many questions in this site and other sites. All of them say that spring constant depends on number of ...
41 views

Educational benefit of putting units outside of variables? [on hold]

When I studied physics (both in high-school and university), in all of the worked examples, variables would be used to denote physical quantities, and thus include dimensional units. For example, ...
33 views

What are the cosmological ramifications if we probabilise and continuify the order of differentiation in $F=\frac{d(mv)}{dt}$?

Newton's second law of motion states that $F=\frac{d(mv)}{dt}$. This is a first-order differential equation, in which the order of differentiation of momentum is 1. So we can write it ...
I've been stuck on what I'm pretty sure is a simple part of a larger question. It's a cylinder (radius a) spinning in a viscous fluid. It's rotating at rate $\Omega$ .During this question we get that ...