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By convention, North and South rank higher in the English language. Thus we have Northeast and not Eastnorth. You have presumed a flat earth. If you start 1.5 km from the North Pole, then after skiing 3 km east and 1.5 km north, you will be at the North Pole, 1.5 km North from your starting point.


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I am an undergraduate physics student working on device physics of organic semiconductors in a chemistry lab. From my elementary understanding, there is a big difference in charge transport of these two semiconductors. In bulk (inorganic) semiconductors, I believe that charge normally flows (not sure what this means), where as in organic semiconductors ...


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The problem in answering this question is that the term wave itself is so loosely used to define that which we observe. But fundamentally a wave is just an expression of the flow of energy in time and space. It's observable evidence that energy is flowing. It's clear that traveling waves expresses the flow of energy. And the interference or superposition ...


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$f(x-vt)$ isn't the general formulation of a wave, but is the general expression for a travelling wave. Also, a standing wave can be transverse or longitudinal (on a guitar string or inside a laser cavity it is transverse, inside a flute it is longitudinal). The reason you can hear the sound of a flute is because some of the energy coming from the standing ...


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Terms like "Father of Physics" (or "Father of Modern Chemistry", or "Mother of Computer Science") aren't official titles, they're just subjective opinions. No one appoints them. Calling Einstein the Father of Physics is like giving your dad a "Best Dad in the World" mug--it's a nice gesture, but no one ever did a survey of every dad in the world to ...


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The (Lie-)group $U(1)$ is the topological space $S^1$ (what we call a circle together with its standard open subsets) together with a rule how to multiply its points. In its representation as numbers in ${\mathbb C}$ with absolute value $1$, we have ${\mathrm e}^{{\mathrm i}\alpha}\bullet{\mathrm e}^{{\mathrm i}\beta}:={\mathrm e}^{{\mathrm ...


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I don't think there is a universally agreed phrase to describe this, but I think the closest is the principle of geometrical reversibility.


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Engineers created that problem. ;) (probably not) Many physics books use $Y$ for Young's modulus (Symon, Knight, Young & Freedman). Taylor's Classical Mechanics uses YM. Halliday, Resnick & -fill-in-the-blank- state that engineers use $E$. I suspect that physicists started using $Y$ for exactly this reason: to highlight a difference in the meanings ...


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Coincidence, nothing deep I'd say. Note that the equation representing the electric field modulus depends on the units you've picked and as such putting so much emphasis on the exact characters appearing in the eq. is senseless. Note that it's possible to form many physics equalities and equations involving 3 characters. E, epsilon and sigma are quite used. ...


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Yeah, that's just a coincidence. The easy way to see this is that $\epsilon$ is a relatively static property of a dielectric but a totally dynamic property of a stretching material.


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Just a coincidence. There are too many quantities and not enough letters. It probably does make a difference that the fields in which these two equations exist (material science and electromagnetism) are well enough separated that you typically won't see them both in the same papers or textbooks; if that weren't the case, people would start using different ...


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Consider the following model of an atom: Keep in mind that it is only a model and while it is a good model that elevates our understanding of the subatomic world, it is still just a model and reality will look different. How exactly? We don't know. The model is good enough, though, to understand what an excited atom is. With this caveat out of the way, ...


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Introduction In general, a Physical System State is described by a set of variables Let’s consider the “System Internal Energy” variable System States A System is said to be in its “Ground State” when it is at the lowest possible energy level Any other State is then an “Excited State” and they would correspond to energy level greater than the ground ...


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Basically electrons prefer to stay in least energy level in an atom. If certain amout of energy is given to it then it jumps to a higher energy level. There are discrete enegry levels so e- would accept only some particular energy to get exicted to higher energy level. When it returns to a lower state it gives out the energy in form of photons. Search ...


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Excitation is an elevation in energy level above an arbitrary baseline energy state. "In English, please!" So what this is effectively saying is that an atom is considered "excited" when its energy level is higher than the rest. This can be manifested as heat, light, etc. For example, the Aurora Borealis. The Aurora is when radiation from the sun ...


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This is how I understand it. There is a series of definitions used in physics, and one used in engineering mostly. I'll describe the one used in physics first: In mechanics, we describe the motion of bodies, and the causes that effect them. This includes the special case where the "motion" is no motion, i.e. bodies are stationary. The description of the ...


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As a native English speaker, I don't even see three definitions. The first two sounded 100% the same all the way up until you wrote the third. At which point the first one sounded pretty meaningless. You could just say motion if you meant any possible motion. To do science we have to make predictions. Which means you predict that one thing happens as ...


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Let's say you are doing a typical SR experiment and you have Alice and Bob flying around in spaceships and such and you have each ship feeding you data. Things outside look one way to Alice and a different way to Bob because of their inertial frames. Let's say they're observing two supernovas and trying to determine their timing relative to each other, and ...


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Boosting means you are changing a frame of reference; boosting frames doesn't imply any actual motion. When you talk about boosting, you are talking about changing the way you are observing something instantaneously. Acceleration on the other hand, is a type of motion inside a frame of reference. When you talk about acceleration, you are talking about a ...


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I might use "boost" for a short burst (more like an impulse) and "acceleration" for a more prolonged burst - but both imply a force applied for a certain time in order to effect a change in momentum. I recommend you ask your professor for clarification. He/she must have had a particular application in mind. In the case of orbital mechanics, the calculations ...


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What's "prompt" depends on just what you're doing. One second is a brief time interval if you're interested in radiological shielding, but an eternity if you're interested in the spectroscopy of a single nucleus. For instance, suppose you have neutrons capturing on some material. The neutrons typically capture in some very excited nuclear orbital and ...


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As Qmechanic pointed out in the comments, you're mixing Einstein and abstract index notation a bit. To make things absolutely clear, we will use early Latin indices for abstract indices $(abc)$ and Greek indices for component indices $(\mu\nu\rho)$ and will always indicate Einstein summation explicitly. First and foremost, an abstract index is nothing more ...


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A Journey into Gravity and Spacetime is John Wheeler's attempt at a popular yet comprehensive explanation of general relativity. He tries to convey all of the significance and depth of GR without using any mathematics beyond simple algebra and geometry. The explanations are very original and can sometimes be quite hard to follow and relate to GR as it is ...


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According to your links an isolated system is : In physical science, an isolated system is either of the following: 1) a physical system so far removed from other systems that it does not interact with them. 2) a thermodynamic system enclosed by rigid immovable walls through which neither matter nor energy can pass. A closed system In ...


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Diffraction occurs when the wavelength and dimension of aperture or slit through which it is passing becomes comparable. When the dimension of the respective system is much larger than the wave length we can neglect the wave properties and consider it to be a ray.Depending on this two different cases we use the terms "geometrical optics" or "physical ...


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A ray is a simplified (asymptotic) description of a wave (which is a field) for the case when neither diffraction or scattering have to be considered. Ray optics requires that the curvature of wavefronts be large compared to the wavelength. JQK is correct that birefringent media require a slight modification of the simple ray algorithms for reflection and ...


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The ray is associated with being normal to the wavefront. However, the ray concept, energy flow, and wavefront somewhat breakdown when you're in birefringement media.


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You're more or less correct. The ray is the limit of a wave where interference effects go to zero, and we can then treat light classically using ray diagrams and such.


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A real force has a reaction force. A pseudo force has no reaction force.


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Real forces are those which arises due to actual interaction between objects.But pseudo forces are not result of any interaction between objects rather it arises due to change of frame of reference and that is why it is pseudo.For example let us consider a person standing in a lift and suddenly the lift is accelerated downward.Now you can see that from a ...



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