Confusion Definition and 1000 Threads

Hi, I am a high-school student who recently finished the chapter on QM. I thought I completely understood it, but when I started to look back at what I’ve learnt, then suddenly, nothing really makes sense. And one of the things I find really really hard is the nature of electrons. My...

I've learned that a force is said to do work when it acts on a body and causes a displacement in the same direction of the force and that W = F.s ( when theta equals zero) But I have a problem understanding the concept. On Pushing a brick wall, carrying a bag heavy brick at a constant height, it...

Lets consider an ideal transformer in no-load state, i.e. with the primary side connected to a voltage source, and the secondary side in open-circuit. Now, this is what I believe; the voltage Vp in the primary produces a current, which lags the voltage by 90°, as would be in an inductor. This...

Hi! I am having a hard time with residues. :( I understand the formal definition of a residue, but anything past that and I am struggling. My course lecturer has a very confusing way of organising the course material and it is very hard to comprehend so was wondering if anyone could help with...

Hi, I was taught that a standing wave is formed when a progressive wave meets a boundary and is reflected. I was also taught that waves that meet a fixed end, reflect on the opposite side of the axis to the side that they met it at. (I hope that makes sense) If this is true, when the wave is...

Hello there. New here. I have read and tried to understand the Kelvin Plank statement of the second law. Essentially, it would imply, it is impossible to convert a given quantity of heat completely to work. Why is it so? I mean, what is the justification for this? I am ready to...

Hello. Electrical conductivity is written as \frac{n_{e}e^{2}}{m_{e}\nu_{ei}} where n_{e}, e, m_{e} and \nu_{ei} are for electron density, charge, mass and electron-ion collision frequency. According to Wikipedea, http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity Unit...

If I understand it, Hilbert spaces can be finite (e.g., for spin of a particle), countably infinite (e.g., for a particle moving in space), or uncountably infinite (i.e., non-separable, e.g., QED). I am wondering about variations on this latter. The easiest uncountable to imagine is the...

A point has no dimension and a line, which has dimension, is made from points together. How does something without dimension create something with dimension? I can't really make any sense of it. Could you share your opinions?

Please look at pictures. What is it that Fv-Mg=-Ma? This does not make sense to me. Fv applies torque while Mg is a translational force. How can a force that is applied perpendicularly at a point of other than the center of mass cause translational motion?

This question is in this rubric because I figured it belonged to measure theory, but I am ready to move it if I am wrong. In reading "Fractal Geometry" by Falconer, I see (Thm. 16.2 and comment following its proof) that the Hausdorff dimension of a Brownian sample path (a continuous function...

Folks: I have a FORTRAN program published in Multivariate Morphometrics (Blackith and Reyment - 1971). In this book they list a FORTRAN program that computes Canonical Correlates. I don't have a FORTRAN compiler and I'm trying to translate this program into PERL. The one FORTRAN book that is...

C) How did they go from the first red line to the second? f) How did they go from the first green line to the second g) B + B(bar) = 1, so surely the answer should have a +1 ? 2) How did they go from the first purple line to the second? I have a list of the Boolean laws and I have used...

Hey all, Quick question about BZ's and it's probably a really dumb one. Solid State isn't my favorite class... What does it physically represent? Like is the area of the BZ divided by the area of a k-state (2π/L) equal to the number of charge carriers in the system? So if there was an...

This is how I learned about Green's functions: For the 1-D problem with the linear operator L and the inner product, (\cdot,\cdot), Lu(x) = f(x) \rightarrow u=(f(x),G(\xi,x)) if the Green's function G is defined such that L^*G(\xi,x) = \delta(\xi-x) I understand how to arrive at this...

Homework Statement A 2 kg mass with initial velocity v = (5i + 7j) collides perfectly elastically with a 3 kg mass with initial velocity v = (-1i -3j) After the collision, the 2kg mass has a speed of √50 m/s and the 3 kg mass is traveling at an angle of 329.77Θ as measured from the...

Given a curve ##\gamma: I \to M## where ##I\subset \mathbb{R}## and ##M## is a manifold, the tangent vector to the curve at ##\gamma(0) = p \in M## is defined in some modern differential geomtery texts to be the differential operator $$V_{\gamma(0)}= \gamma_* \left(\frac{d}{dt}\right)_{t=0}.$$...

Hi, I'm really confused with how electrons become 'free' in a metal. I have a few questions and would be very grateful if someone could shed some light on them. 1. Are the electrons actually free? In a sense that the atom it is attached would essentially become an ion 2. If you take a copper...

Hi. I am confused a bit about the solution for 2:4 decoder in the picture below. Please help me with the question in the figure. Thanks.

I am trying to convert a FORTRAN version of a Canonical Correlates program listed in Multivariate Morphology - Blackith and Reyment. I've programed in FORTRAN decades ago and now I have to understand the language to rewrite the program into PERL. a) DO 260 I = 1 , M b) SX( I ) =...

I understand why an object in a moving frame would be longer, but not why one in a stationary frame would be shorter. Wouldn't one in a stationary frame be the same as the object would be in the rest one? I understand the time dilation behind it, it's just that the rest of the reasoning makes no...

In "A Student's Guide to Vectors and Tensors" by Daniel Fleisch, I read that the covariant metric tensor gij=ei°ei (I'm leaving out the → s above the e's) where ei and ei are coordinate basis vectors and ° denotes the inner product, and similarly for the contravariant metric tensor using dual...

My mcat book says temperature is a measure of the total kinetic energy of a system. Then later on it says temperature is a measurement of the average kinetic energy of a system. Is this an error? Thank you.

Hi all, I'm sort of struggling to understand the difference between active and passive transformations. I'm working with two books, and both say that in one case the vectors are transformed (active) and in the other the operators are transformed (passive). That's fine and dandy, but in terms...

If you have a charged solid sphere with uniform volume charge density ρ, then the total charge on the sphere is Q = ρ*4/3*∏*R^3 , where R is the radius of the sphere. Now...

In a recent physics class I took, my teacher explained how friction is not affected by surface area, but by the "bumpiness" of the two objects and the mass, as well as other things, but not the surface area. But this made me wonder how nails get harder to pull out the deeper they are embedded in...

Homework Statement A dog takes a running horizontal leap off a 10 m cliff and jumps with a speed of 3 m/s onto a ledge 4 m below the height of the cliff. With what speed does he land on the ledge?Homework Equations KEi + PEi = KEf + PEf 1/2mvi2 + mghi = 1/2mvf2 + mghfThe Attempt at a Solution...

Power loss doubt: power loss = I^2 R Power loss = V^2 / R But the 2 equations are contradictory ,,, from the first equation , we can say " MORE THE RESISTANCE MORE THE POWER LOSS" from the second equation ,,, it is the other way round... Why does this happen? ( usually the 1st equation is used...

Newton's third law confusion? If A exerts some force on B then it experiences a force of same magnitude and in opposite direction. This didn't seem intuitive to me so I thought of it this way, Let A and B be a single system. Now there is no net external force acting on the system so the...

I'm watching a lecture on Newton's method with n-dimensions but I am kind of hung up on why the professor did not use the negative sign while taking the first gradient? Is there a rule that explains this or something that I'm forgetting? The rest makes sense but highlighted in red is the part I...

I'm watching a lecture on Newton's method with n-dimensions but I am kind of hung up on why the professor did not use the negative sign while taking the first gradient? Is there a rule that explains this or something that I'm forgetting? The rest makes sense but highlighted in red is the part I...

Homework Statement Convert -2+2√3i to polar coordinates. Homework Equations r = √x2+y2 θ = tan-1(y/x) The Attempt at a Solution I am confused because θ = tan-1(2√3/2) = tan-1(√3) = -π/3 and r = 4, so that would make the polar form 4cis(-π/3), but the calculator gives: 4cis(2π/3). I...

Homework Statement My snipping tool is totally broken. So I'm going to leave a link :x It's problem 1.6 http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/assignments/ps1a.pdf Homework Equations E_{sheet}=\frac{σ}{2ε_{0}} E_{slab}=\frac{ρD}{2ε_{0}}...

Homework Statement A 50 KVA,6360 V/230 V transformer is tested on open and short-circuit to obtain its efficiency,the results being as follows: O.C.: Primary Voltage-6360 V, Primary Current-1 A, Power Input - 2 kW S.C: Voltage across primary winding-180 V Current in secondary...

So a coherent state in quantum mechanics is "the most classical" quantum state (A Gaussian wave packet), which satisfies the Heisenberg uncertainty relation with an equality. This allows the wave packet to travel in space in a more localized fashion (like a classical particle) because its...

When deriving capacity of a parallel plate capacitor, we consider the electric field (sigma/epsilon), i.e. the field due to one of the plates while both the plates are charged with Q and -Q respectively...so should not be the field due to both the plates, i.e. (2sigma/epsilon) since the...

Follow the 1st ideia: \\ d\vec{r} = dr \hat{r} + r d\theta \hat{\theta} \\ \\ \frac{d\vec{r}}{dr} = \frac{dr}{dr} \hat{r} + r \frac{d\theta}{dr}\hat{\theta} \\ \\ \frac{d\vec{r}}{dr} = \hat{r} and now: \\ \frac{d\vec{r}}{dr} = \frac{d\vec{r}}{dt} \frac{dt}{dr} = \frac{d\vec{r}}{dt}...

suppose that you have to wires connected in parallel, one double the length of the other now that means that the longer wire has double resistance . according to kirchhof's law , the current going in the two wires is the same as the current coming out , but if one is double the length of the...

Hi all, I tried searching for this but failed to find an answer to my question. I am having an issue with properly interpreting the equations for time dilation and length contraction. Let's assume that I am standing still and a train is passing by next to me (moving with uniform velocity). Let...

Hi. For whatever reason I'm really struggling with figuring out the direction of a moment in two dimensional statics problems. How can I tell if it's CW or CCW? The right hand rule just confuses me even more and I cannot find any explanation that breaks it down simply enough for me to...

This paper, http://arxiv.org/abs/1402.3055 Black Holes, Firewalls and Chaos from Gravitational Collapse, reminds me why it is risky to get too close to a black hole. The authors suggest some the paradoxes posed by black holes may be a consequence of the cosmic censorship hypothesis. I may have...

So the voltage across the R2 resistor is given as vT-0 = vT But then the voltage across the R1 resistor is given as "vT-Vs1" I'm not sure which two nodes the voltage across R2 involves. Is it the same as R1? Also, I am not sure of the voltage source vs1. Across which two points does it apply?

Homework Statement The diagram: http://images.fr1ckfr4ck.fastmail.fm/probC.jpg This MOSFET has the following parameters: |VT| = 0.6V μpCox = 100 (μa/V2) L = 0.25μm λ = 0 Establish a drain current of 0.8 mA and a voltage VD of 1.5V. Determine the transistor width W, and the...

Homework Statement I have been doing dot and cross product recently. I get how to calculate everything; however, I am confused about which angle to use when asked to find the angle between two vectors. When you use the cross product, you always end up with 2 answers, for example 120° and...

My professor confused me today :( I'm trying to figure out the thickness of an anti reflection coating and it looks like from the equation 2ndcos(Θ) = mλ that for a given λ the thickness of the film should increase for incidence slightly away from normal. But he said that intuitively it...

Hi guys, The other day I found myself asking the question below and couldn't quite manage to re-align my own personal experience with E&M theory. I am sure it will just be a gap in my knowledge base of E&M. The Question: If you are contained within a metal mesh cage which acts as a...

Hello friend... I have confusion in understanding the concept of viscosity. Please help me. Viscosity is the property of the fluid which offers resistance to the movement of one layer of fluid over another adjacent layer of the fluid. Here both top and adjacent layer causes shear stress on each...

This is about Hans Ohanian, "Einstein's E = mc2 mistakes," http://arxiv.org/abs/0805.1400 , a historical paper that discusses whether Einstein's original proofs of E=mc2 were really valid. My general understanding of the topic is as follows. I'm just discussing SR, not GR. What's really...

I can't figure out what actually is the Pich-off voltage of a JFET. I basically have confusion between these two definitions: Pinch off voltage is that gate source voltage at which there is no drain-source current Pinch of voltage is that 'Drain-Source' voltage after which the drain source...

So I just started taking Modern Physics and we are currently discussing special relativity. And needless to say, its giving me a headache. Here's my confusion: First, my Professor is Russian, and while his accent isn't so thick that I can't understand him, his grasp of English itself, is such...