Confused Definition and 1000 Threads

I've stumbled over this article and while reading it I saw the following statement (##\xi## a vectorfield and ##d/d\tau## presumably a covariant derivative***): $$\begin{align*}\frac{d \xi}{d \tau}&=\frac{d}{d \tau}\left(\xi^{\alpha} \mathbf{e}_{\alpha}\right)=\frac{d \xi^{\alpha}}{d \tau}...

I worked out the expectation values of the components of a 1/2 spin particle. However, I'm confused about Griffiths notation for the x and y components. For the x component I got, ## \left< S_x \right> = \frac \hbar 2 (b^*a+a^*b)## which is correct, but Griffiths equates this to ##...

Hello, Sorry if this is the wrong section of the forums, but I figured that questions about mutually exclusive events are relevant to probability. My current understanding: Two events are mutually exclusive if both events cannot occur at the same time. In other words, two events are mutually...

Hello! I am a bit confused about the systematic errors in experiments. For example, say that a mass scale was not calibrated and indicates 1g bigger all the time and I want to publish a paper in which to quote some measurements made with that scale. Let's assume that the value obtained, without...

Hello. Recently we began taking static electricity and our teacher asked us to do a research paper on static electricity and charges in general to help us understand the material better. I've been stuck a bit on trying to understand what's the difference between polarization and induction and...

Hi. I am confused about the use of Newton's 3rd law in the following situation. If someone steps horizontally out of a skyscraper with zero vertical velocity. Then obviously they fall downwards. But if i apply Newton's 3rd law ; persons weight act downwards on the air so doesn't the air apply an...

i have been researching how to build a boost converter. according to the articles i have read, when the switch is closed current flows through the switch to the negative terminal. when the switch is opened, the back emf from the inductor and input voltage add, which forward biases the diode. i...

I was able to derive, ##1/2*1*v_1^2 = 1/2*4*v_2^2 \\ v_1=2v_2 ## But I am confused whether the ratio is 1:2(Looking at the coefficient) or 2:1

I have just finished my 1st year as an undergraduate in Computer Science in the UK. Having always loved Mathematics up to an insane extreme, I was very disappointed with the course. It barely required any Maths, and most of the time it was just about arithmetic or simple discrete maths. I really...

Hi all, I just finished up my master's degree a few months ago, during which I did my thesis work at another university. The work I did was very exciting and gratifying to me since I plan to continue in the same field. As a result, I had asked my supervisor if there were any research...

Okay, I am confused about work and what it is. I know the formula, W=FDCos(theta), so putting it in math terms doesn't help. I am trying to get a layman's/physical understanding of it. Everything I read says it is equal to energy, so then I think it must be energy right, has same units? But...

Hi Im current in last year of HND mechanical (100% distinction so far) and have HNC in general engineering (100% distinction). Im better at the research and piratical bad at exams (diffucult reading and writing and slow comperhention skills and expression using writting what i want to...

Hello! I am a bit confused about the distinction between virtual and real particles. For example a Z boson, which has a very short lifetime, in all experiments will decay to some other stable particles (i.e. it is detected through its decay). This means that it will always appear as a...

Summary: I'm stuck on this simple excersize, to show that in this coord transform, despite x = x', d/dx != d/dx' From "Intro to Smooth Manifolds" (this is a calculus excersize), The Problem I have is with showing d/dx != d/dx' When I write out the Jacobian matrix, I get exactly d/dx = d/dx'...

Hello everyone! Recently I saw this paper: https://arxiv.org/pdf/1304.4801.pdf ("Any nonlocal model assuming “local parts” conflicts with relativity " by Antoine Suarez). He mentions standard experimental configuration with beam-splitters and detectors. Then he distinguishes possible models...

Summary: Lower than average weight at the equator causes the Earth to be wider, yet positive gravity anomalies are claimed to cause an increase in sea height. Summary: Lower than average weight at the equator causes the Earth to be wider, yet positive gravity anomalies are claimed to cause an...

So I'm a chemistry student here in the UK - and I'm feeling a bit like a fish out of water on a physics forum but... I'm having trouble with a derivation that seems simple but i can't for some reason seem to understand. I know that the energy of a photon is given by E=hc and that c=lambda*v...

Summary: Trying to understand pressure and it's relation to force Okay here is my dumb thought. A force is defined as an influence on an object, causing change in motion correct? Then how can pressure be a force on an area? Maybe I'm stuck on the word "on". But the way I'm reading the force...

Summary: Should both envelope detection and windowing+overlapping be used before FFT? Summary: Should both envelope detection and windowing+overlapping be used before FFT? Hi everyone! I'm somewhat a newbie to signal analysis, but I've also noticed that there seem to be many different...

So the equation for work is W = F * s F = m * a, so W = m * a * s Transferring this to units of measurement gives us: J = kg * m * s-2 * m Or simplified: J = kg * m2 * s-2 Transferring back to units of quantity: W = m * v2 How can that be correct? Obviously Ekin = 1/2 * m * v2. Where did that...

I might be a slow learner, but am still trying to understand the difference between field lines and vectors. I've got that magnetic field lines are symbolic and that the directional arrows applied (from north to south) are a convention. But see the attached image. The field lines form a closed...

Hello! As far as I understand, in QFT the interaction between particles is mediated by the exchange of a boson. When doing calculations, one assumes that you have 2 free particles coming in, they interact at a point by exchanging a boson and then they propagate again as free particles, and this...

There seems to be different forms of this lemma which conclude different things, yet they all seem to go through the same steps, so I figure that they must be related somehow. I'll start with the form that I understand: Considering a pair of primitive polynomials A( x ), B( x ), such that C( x...

I’m at the point in my career where I’ve been accepted to a few grad schools and am currently deciding where to go. My top priority is advisor fit, since I plan to stay in my field. Talking to multiple professors/scientists at different institutions, it seems that my success in grad school is...

Our teacher taught us "Laser" today and it made me confused. So Electron s energy in n=1 is around 13 eV (-13eV) and in n=2 is around -3.4 eV. Our teacher told us if we radiate a photon which has 9.6 eV energy (the difference energy of the first and second layer, n1 and n2, which is 13-3.4=9.6...

Ok, i am struggling to figure something out. I don't know why math is so much easier than physics haha. ok, here is my struggle. I have two states, state 1 and 2, which i will call just 1 and 2. 1: T=298kelvin V=0.025m(cubed) P=310Kpa Mass1=Mass2 R=0.2870 2: T=323kelvin V=0.025m(cubed) P=...

Hawking Radiation says that an antiparticle and particle spontaneously appear and annihilate each other everywhere, but at the horizon, if the antiparticle appearing inside the horizon and the particle appears outside, then the antiparticle is sucked in and the particle is emitted outward...

Homework Statement A dilute gas of N non-interacting atoms of mass m is contained in a volume V and in equilibrium with the surroundings at a temperature T. Each atom has two (active) intrinsic states of energies ε = 0 and ∆, respectively. Find the total partition function of the gas.Homework...

I never really understand the concept of entropy through classical thermodynamics. Here are a few questions. 1. The change in entropy dS in an isolated system is always >=0, but how does it imply the system tends to a state with maximum entropy? How to know that there exist a maximum? 2. Why is...

Homework Statement On my attached pic "wtflang2," he says X' must lie on the segment between P' and Q', but the picture is not indicating that. X' seems to be on a segment P'X', not on segment P'Q'.Not only that, but he says d(P,X) and d(P',X') should be equal but his picture does not show...

HiI was reading about capacitors and potential energy. But the equation seems counter to how i thought. For potential energy you have: U = Q^2 / 2C or U = CV^2 / 2 But doesn't this suggest you lose potential energy the more capacitance you have? Since in the first equation as C increases U...

So let us say that there are 3 separate alien species that somehow speak and write the same language. Let us say that 2 of these have always lived and died in their spaceships/asteriod ... going at speeds close to that of light. Alien species 3. A3 leaves behind a message saying that at time t0...

Homework Statement A vertical block-spring system on Earth has a period of 6.0 s. What is the period of this same system on the moon where the acceleration due to gravity is roughly 1/6 that of earth? Homework Equations w = √(k/m) w = (2Pi)/T T = 2Pi*√(m/k)[/B] The Attempt at a Solution So...

Hi again. I have one other problem I'm puzzled about. (a) A sorting algorithm takes one operation to sort an array with one item in it. Increasing the number of items in the array from n to n + 1 requires at most an additional 2n + 1 operations. Prove by induction that the number of operations...

Homework Statement A 3.20kg rubber ball drops from a height of 4.80m to the ground a bounces back to a height of 2.70m a) how much potential energy does the ball lose on the trip down? b) how much energy does the ball regain on the trip back up? c) what is the net loss of potential energy...

Homework Statement If an atom in energy level 1, how many absorption spectral lines can an atom exhibit due to transition between 3 levels? How about 4 and 5 levels? And also in emission? Homework Equations Concept The Attempt at a Solution I am confused one book says it can absorb a photon...

In the textbook (attached image) it says that the boundary condition is V=0 at r=R. This creates a correlation that ##B_l=-A_l R^{2l+1}## but the potential at any boundary is continuous so when we take this account, we get. ##B_l=A_l R^{2l+1}## These two clearly contradict each other. I'd...

Homework Statement This is for a lab report and I am just confused about how I should regard volume because this issue is affecting 3 other questions. If you heat a gas in a closed flask that is connected to a manometer with water in it, the water level goes up (the arm open to atmosphere rises...

Homework Statement So i have this lab where I am supposed to push a car up an inclined ramp. I record the time it takes for the object to reachest the highest point on the inclined ramp before it goes back down. I am supposed to create a position vs time graph, velocity vs time graph, and...

Homework Statement I've an equation here: h = 3270 Pa / 1,0 g/cm^3 × 9,81 m/s^2 = 33 cm How did those units cancel out to make it cm? That's something I don't get. Homework Equations Given above. The Attempt at a Solution I've tried to cancel them out by looking at the same unit in the...

(mentor note: this is a homework problem with a solution that the OP would like to understand better) In Taylor's Complex Variables, Example 1.4.10 Can someone help me understand this? I don't know what they mean by (i, i inf), or how they got it and -it

Homework Statement Homework Equations E=KQ/R^2 The Attempt at a Solution I'm kinda confused at what the question is asked. It is in terms of x, but I thought the integral for potential is V=int(Edr)? Also, should it be integration starting from infinity? Why is the integration from -2 to 3...

Homework Statement My textbook is no help, my teacher is no help, so I've found myself here. I am having a difficult time understanding the differences in 1.Electric Potential energy 2. Potential Difference 3. Electric potential Im sure this question has been asked tons of times but I need...

Homework Statement Hi guys, Sorry in advance for posting this type of question in this section as I'm sure it belongs somewhere else, however it technically still is homework for me as I'd really like to be able to get good at this. Personally I've never been great at rearranging equations to...

Hey! I'm confused about this: ½v21 = ½v20 - gh1 v21 = v20 - 2gh1 v1 = √v02 - 2gh1 Soo, what basically happened here when solving the equation for v1? I understand that the equation should be multiplied by ½ and then take a square root in order to solve for v1, but what's that factor "2"...

Two batteries connected in series feed a 0.16 Ohm resistor with 80 Watts of power at 3.85 Volts. Each 4 Volts battery is capable of supplying up to 20 Amps of continuous current. Ohm's Law calculation gives 22.36 Amps of current draw for the entire circuit but ... Question 1: How much current...

Hello everyone! It seems to me that there are many ways of calculating SNR depending on the type of signal and the nature of problems. I was able to get a decent amount of information for electrical signals but couldn't find resources which discuss the topic in a more generalized manner. I was...

So I've been working on Pythagorean stuff and it's pretty straight forward but then I got confused over something quite simple. It's a geometry question so I'll try my best to illustrate the question. So there's a triangle and we must evaluate whether it's a right angle. The lengths are not...

Given two probability distributions ##p \in R^{m}_{+}## and ##q \in R^{n}_{+}## (the "+" subscript simply indicates non-negative elements), this paper (page 4) writes down the tensor product as $$p \otimes q := \begin{pmatrix} p(1)q(1) \\ p(1)q(2) \\ \vdots \\ p(1)q(n) \\ \vdots \\...