Confusion Definition and 1000 Threads

Hi all, I have a severe confusion about the time-ordering operator. It is the best thing ever, I think, since it simplifies many proofs, due to the fact that operators commute (or anti-commute, but let's take bosonic operators for simplicity) under the time-ordering. However, sometimes I...

Good evening people. Recently I started taking the "electric network analysis" course in my school. We already saw the mesh analysis method for solving circuits. Now we are seeing the node analysis method. I understand that the first step for this method is finding the number of nodes (and one...

I don't get DC. How do the electrons flow from one side to the other? Wouldn’t the electrons on both terminals just meet in the middle because of their attraction?

Homework Statement I have the solution and everything, I'm just confused why they use cos for Fy and sin for Fx ... Homework Equations I've always known Fx=Fcos and Fy=Fsin .. but now I am getting to different problems and it confuses me The Attempt at a Solution I read many posts and answers...

Why does Wikipedia's page on electrical charge have a picture of a positivity charged object with arrows going to a negatively charged object? Doesn’t electrons flow from a negatively charged object to a positively charged object? Or is the picture just showing conventional current? Thanks.

Hi all! I know that this might be a stupid question, but I am very confused about a particular aspect of the electric field. I have seen these equations: E=-∇V and E=-∇V-∂A/∂t Could you guys explain how the electric field can be explained with or without -∂A/∂t

Hi again I'm trying to graph a function in WolframlAlpha, but I can't figure out how to set limits on the x-value's domain. Is that an option for that site? I'm trying to do this function set: _____ 4-x^2, x < -2 h(x) = 3 + x, -2 \le x < 0 _____x^2 + 1, x \ge 0 It's hard enough to...

I hope this is in the right thread, I wasn't sure which one to put this in but this seemed like the most likely one to be right, so I'm sorry if this is in the wrong thread. Anyway, my question basically amounts to this: what is the difference between something orbiting around a still planet...

So the definition I have seen is: Given a topological space <S,F> it is compact if for any cover (union of open sets which is equal to S) there exists a finite subcover. By the definition of a topological space both S and the empty set must belong to the family of subsets F. Wouldn't <S, empty...

Homework Statement Homework Equations principle of moments Newton's 3rd law The Attempt at a Solution Okay. I am not asking how to solve this question. I just have a little misunderstanding of the concept of the Newton's Third Law. I will get straight to the point. For example, in this...

I was trying to understand a few of the relativity basics that seem to have me confused. Below is a thought experiment and some questions, I would really appreciate any help to improve my understanding. Thanks Imagine a large, circular, tube like space station. Free to spin around the inside...

Hi, I am not sure what $ {f}^{*}({z}^{*}) $ means? I think the '*'s cancel, ie $ {f}(z) = u(x,y) + iv(x,y), \: \therefore f({z}^{*}) = u(x,y) - iv(x,y), , \: \therefore {f}^{*}({z}^{*}) = u(x,y) + iv(x,y) $ ? Thanks

This is something that's bugged me since I've read about it. What does it mean to say "energy is the capacity to do work"? I've read somewhere that work is some sort of integral. But I'm still confused, what do we mean when we say "the energy of object x is so and so"? I know the two quantities...

I uploaded my question below; basically I am confused in part b) where they show that: 50 kgm/s = (5kg)v2 - (5kg)(-4m/s) then they say that 30 kgm/s = 5kg v2, but shouldn't it be 70 kgm/s = 5kg v2? As noted at the beginning of the question North is positive and thus since the cart moves south...

Index notation in GR is really confusing ! I'm confused about many things but one thing is the order of index placement , ie. is Λa b the same as Λba ? And if not what is the difference ? Thanks If anyone knows of any books or lecture notes that explain index gymnastics step by step...

http://www.majordifferences.com/2013/06/difference-between-incomplete-dominance.html#.VYwirvmqqko in 5th point of codominance it is written that That in codominance " quantitative effect is absent." Why?I am really not getting?As far as I know codominance has genotypic ratio of 1:2:1 and so is...

Some days ago I got confused trying to solve an exercise about fluid dynamics. Trying to simplify the problem here is a similar situation: I have a cistern connected to a tube containing a fluid as shown in the picture below. Assumming that the fluid is incompressible... I know from the law...

I've found this a very confusing thing:when we locate the second dark fringes above and below the central maxima,we divide the slit into four parts and claim that pairs of waves interfere destructively as the path difference would be wavelength/2.But what if we just divided it into two parts and...

Hello, I am having an issue understanding something about the RCS of a sphere. The radar cross section of a sphere in the back-scattered, mono-static direction is simply equal to the spheres cross sectional area, for wavelengths much less than the circumference. In the following link...

There is no such thing as absolute motion or rest. This is because one can record the speed of an object moving relative to it and find that it is in motion. The same holds for the object in motion. An observer on the object will observe the other observer moving relative to him. The measured...

I am currently reading "Differential Equatons with Applications" by Ritger and Rose, and I need some clarification about some notation and convention that they are using. I think it all stems from a lack of clarity of the difference between the operator d/dx and the "object" (I don't know what...

Hello. I need some help understanding time dilation. So the idea is that moving clocks tick slowly. Say there was an observer A who, by his frame of reference, is stationary, and he sees an object B moving past it at high velocity. From what I understand, to A it would appear as if B's clocks...

Homework Statement a particle on a slope with angle theta with no friction. v(0) = 0, x(0) = 0, with coordinates i down the slope and j normal to it. I am confused about why with the constant velocity forumla I get a different answer to my attempted method.. I can't see what's wrong..I need to...

Question already asked on http://math.stackexchange.com/questions/1310194/confusion-about-a-random-process?noredirect=1#comment2661260_1310194, but couldn't get an answer so reposting here...

Muon created by fast cosmic ray has speed 2.99X10^8 m/s and life time 2.2 micro sec. According to this numbers muon should travel only 0.66Km with respect to Earth in his life time. however it travels more than 10 km (10.4km) due to time dilation. in muon frame of reference, Earth travels only...

Hi all, quick question about a PLA circuit I'm doing for coursework. I'll upload a pic of the circuit to help explain. I've got the main stuff worked out but a little line in the coursework is making me think if I need to add a couple of extra connections on it. The circuit has 7 incrementing...

For me BIOS and UEFI is all now confusing :-) Is there any element similar to BIOS in UEFI? When a UEFI based PC starts, is there any BIOS component, 16 Bit real mode starting from Reset Vector that still runs and then it actually loads UEFI or is it the UEFI firmware right from the very...

Alright here's my confusion, if i take say 3x^2 + 4x^2 ill end up with 7x^2 which i accepted was the correct way to think about it, but if i try the same problem without the x variable doing the same method, 3^2 + 4^2 = 7^2 this is obviously not the correct answer. Instead 3^2 = 9 and 4^2 = 16...

Hi! According to this http://en.wikipedia.org/wiki/Electrical_mobility, the definition of electrical mobility ##\mu## is: ##\vec{v} = \mu \vec{E}##. But since electrical mobility is always positive, this means that the velocity is always parallel to the E-field regardless of charge. How can...

Homework Statement The question is made of a smooth inclined ramp at an angle of 30 degrees. There is a particle on the ramp with mass m. The question asks to find R (The reaction force on the ball) in terms of mg Homework Equations Resolving the forces with the ramp and equating upward and...

Homework Statement The distance between the objective and eyepiece lenses in a microscope is 21cm . The objective lens has a focal length of 5.5mm. What eyepiece focal length will give the microscope an overall angular magnification of 350? Homework Equations M=(25*d)/(fe*fo) or...

Define the following $$Z= \begin{pmatrix} 0 & A \\ B^T & T \end{pmatrix}$$ where we define $A$ and $B$ as $r \times m $ matrices and $T$ is an $m \times m$ matrix with nonzero distinct indeterminates at the diagonal, that is, $T_{i,i} = t_i$. What is the meaning of $B^T$ ?

I have a confusion about the rotation of dc series motor..Suppose I put some load on it and turned it on..Due to no initial back emf, high current will flow in the armature (and field) and due to high starting torque, the motor will start rotating at say,1000 rpm. This will induce back emf which...

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an alternating current, an alternating magnetic field is produced, similar to a sine wave. Therefore, I...

Little bit stuck with this practice question for my exams, how do they suppose I work out the length of the individual beams or height of the framework without an initial length? Is there a secret way I've never heard of? Any help would be appreciated, it's foundation degree level but probably...

Hi, I am working on a project and came across a conceptual roadblock. I am working with a PSD, let's say the units are V^2/Hz. I choose a dF based on how many sine tones I want in the time signal I am going to create. I sample the PSD curve at my frequency bin locations; so I have both my...

If a charge is moving in a magnetic field with velocity v, q(vXB) force acts on it. If a current carrying conductor is placed in a magnetic field, it experiences a force BiLsinθ (all symbols have usual meaning). But the reason behind the later force is the interaction between two magnetic...

This is a long one if you have to follow all of my steps. If you are reasonably familiar with Killing forms then you can probably just skip to the three questions. Okay, I'm on my latest project which is to get some idea about how Dynkin diagrams and Coxeter labels work. (How do you pronounce...

As I am new to this forum, I must apologise if I have began this thread in the wrong category but I have a bit of a problem. I don't necessary study physics, I study Electrical Installation at college. As a result we overlap on some physics topics We have recently covered Star Delta. Now, I...

Hi Why are there three types of neutrinos? Why isn't there just one neutrino just like there is only one electron? (I mean electron doesn't have different flavours to it, same with tau and muon.) My textbook touches on this very breifly and confuses me with "if there were only one type of...

Hello everyone! I am new here. I have used this forum on and off through google searches in the past and learned a fair bit from the posts. This is the first time asking anything. The question is probably extremely simple but has been overrun in my head for a week! It is in regards to...

Namaste If escape velocity on Earth is 11 km/s and velocity of Earth is 30 km/s how is that the atmosphere doesn't escape the pull of earth. Is the escape velocity with reference to Earth ? I don't think so because when finding the formula we add kinetic and potential energy and then equate to...

I am confused about black hole horizons and such common statements as "light cannot escape from inside the horizon". The way I currently understand it is as follows : 1. Horizons are always relative to an observer, and what is called "the black hole horizon" is just a shorthand for "the black...

Hello. The skin depth is nothing but measure of penetration depth of EM Wave when it is incident on the conductor. It is well known that the skin depth is decreased when the EM wave frequency increases. But thinking about DC field. We know that when DC is applied to metal (metal is installed...

So while reading some old threads/blog posts on the black hole firewall paradox, it occurred to me that I had some residual confusion regarding why firewalls (supposedly) form at all. IIUC, the argument is that usually, the vacuum is a highly entangled state, and that disentangling it (in order...

Look, I found that there exist two kind of electric current: conventional flow and electron flow. I have read that in every situation I have to use the conventional flow, however I'm going to work with electric circuits using copper wires. In solids, only negatively charged particles (electrons)...

First let me give the definition of tensor that my book gives: If V is a finite dimensional vector space with dim(V) = n then let V^{k} denote the k-fold product. We define a k-tensor as a map T: V^{k} \longrightarrow \mathbb{R} such that T is multilinear, i.e. linear in each variable...

I have been reading optics for the past few months. If light has the property of interference, when I look around, why don't I see any interference patterns. does it mean all the waves around me are in phase ? Another question is, why don't Cellphone signals interfere with each other ? they are...

I know there has been a lot of threads on the forum about this topic, but my question is slightly different from the others. I have recently read this article by Sean Carroll (http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/); now, I'm completely aware (& convinced)...