Confusion Definition and 1000 Threads

Suppose I have two charged particles with charge densities ρ1(r,t) and ρ2 (r,t) with corresponding velocity fields V1(r,t) and V2(r,t). Can I write continuity equation for the combined system? Wouldn't charges moving with different velocities would contribute differently to the current which...

Homework Statement Hello, I'm little bit confused about a particular inequality in a proof: | (D_j f_i) (y) - (D_j f_i) (x) | ≤ | [(f'(y) - f'(x)]e_j | ≤ ||f'(y) - f'(x)|| The last part of the inequality confuses me. Is the absolute value (norm on R) less than any other norm on R^n?

I just started an E&M class and right from the beginning the notation seems so confusing it has to have been done as a joke. Trying to do a problem I run into about 10 different r's I have to keep track of. Capital R Lower case r Lower case r prime The r in spherical coordinates The "squiggle" r...

Homework Statement im supposed to use a direct proof to prove that if 1-n^2>0 then 3n-2 is odd for all n∈Z Homework Equations The Attempt at a Solution if you let n∈z then suppose that 1-n^2>0 then 1>n^2 but the only inter n such that 1>n^2 is 0. 3x0-2=-2 as -2=2(-1), -2 is even ...

We all know that M.I of a Uniform rigid rod about an axis perpendicular to it's length and passing through it's center is MLsquare/12.Where M is mass and L is length of the rod. If it is broken to half such that M becomes M/2 and L becomes L/2,we can't apply ML square /12 formula to it.We have...

Greetings, I am a Physics instructor teaching a course on Physics for Medical Radiologists and have a question to further my own understanding of wave / particle behaviour of X-Rays as used in x-ray image production. My background is more in climate / geophysics. The textbooks available for...

Im not sure how to interpret the notation, specifically the one on the left, the one on the right seems like you just include everything in the universal set? what does it mean when the line goes over everything? what does it even mean when the line is over the and/or symbol

So everyone knows the speed of light is a universal constant. However in many phenomena involving light it is useful to think that light is 'slowing down' like light travels slower in glass/ water then it does in a vacuum. How can this be if it is a universal constant?

Homework Statement A baseball pitcher is known to throw a pitch with a speed of 105 miles per hour. In how many seconds will the pitch reach the catcher if the mound is 20 meters away? (assume 1600 m in 1 mile) Homework Equations v=d/t The Attempt at a Solution Idk how to...

Hi as I'm reading http://www.maths.tcd.ie/~cblair/notes/432.pdf at page 13 I see that he states that the covariant and contravariant field tensors are different. But how can that be? Aren't they related by F_{\mu \nu} = \eta_{\nu \nu'} \eta_{\mu \mu '} F^{\mu ' \nu '} ? and is not the...

The cartesian sign convention for a convex lens is follows: 1. All distances on the principal axis are measured from the optical center. 2. The distances measured in the direction of incident rays are positive and all the distances measured in the direction opposite to that of the incident...

Hello, a confusion has arose during my so far study of the above book. According to the composition rule (2.3.11) it should be: U\left( \Lambda ,a \right)=U\left( \mathbf{1},a \right)U\left( \Lambda \right) and according to transformation law (2.5.3) and the eigenvalue equation which follows...

I read about the random walk the other day. The simplest 2D form, where you start at zero and move up or down one unit at random, both are as likely. To get an the average distance from zero after N steps, the following argument was used: The distance after one step is 1. If after some steps...

If a car is pushing a bus (and the two both move in the direction of the car), I understand that the amount of force with which the car pushes against the bus is equal to the force the bus pushes back on the car. What I don't understand is why the car moves. Is it going forward with the same...

In nodal analysis method, two books use different and contradicting approaches and not sure which one is correct. One books says that currents at each nodes should be treated independently from the other nodes so that the same current can have two opposing directions in the same equations. The...

As far as I understand, the momentum operator is: \hat{p} = -i \hbar \frac{\partial}{\partial \hat{q}} Where I'm not sure at this point if it's mathematically correct to talk about a derivative wrt. the position operator - but the point is, as far as I understand, that this equality is true...

The Dirac delta "function" is often given as : δ(x) = ∞ | x = 0 δ(x) = 0 | x \neq 0 and ∫δ(x)f(x)dx = f(0). What about δ(cx)? By u=cx substitution into above integral is, ∫δ(cx)f(x)dx = ∫δ(u)f(u/c)du = 1/c f(0). But intuitively, the graph of δ(cx) is the same as the graph of...

Confusion on Newton's 3rd law! According to the 3rd law, the equal and opposite forces are acting on two different bodies and therefore cannot cancel each other. They are mutual forces. Why then, so we say the force of gravity on say, a book on a table, and the normal force acting on the book...

Lets take a simple BJR transistor having an Rc. The Ic = beta*Ib, of course. But Ic=(Vcc-Vce)/Rc as well right? Now the confusion, does Ib cause Ic or is Ib possible without Ic (and thus no Vcc)? If we have Vcc and thus Vce than we shall have Ic thus we can have Ib=Ic/beta? What causes Vce, is...

So since we know that electrons are flowing in a relatively less negative (relative positive) direction why does + indicate source? Surely the electrons are flowing towards the + and not from it.

I'm thinking of non pyrotechnic ways to make changes in the velocity of a satellite in space and my concepts here might be totally wrong, but i wondered if transfer of momentum might work. That is, as in the first image if i have a small mass compressed by a spring and i release it later by...

I have a simple question about the notation. I want to be more correct with notation, I don't understand exactly what the notation is saying. In regards to a Metric space A metric space is an ordered pair (M,d) where M is a set and d is a metric on M, i.e., a function {{\bf{d: M \times...

While studying the brillouin zone I came across the dispersion relation and the group velocity. The group velocity is given by v=dω/dκ, I understand this in the sense of beats where it is Δω/Δκ and I understand that the group velocity is the propagation speed of the envelope function. However...

Hey Guys, I continue to get mixed messages about the nature of electron behaviour during the double slit experiment. I have heard the term observation used to describe an interaction with the electron (Obviously necessitating a change in it's behaviour to facilitate the ballistic outcome)...

Homework Statement The problem is attached Homework Equations P=F/A The Attempt at a Solution I did the question like this (got wrong answer though): Surface area of sphere=4∏r2=4×∏×0.252 Atmospheric pressure=1.01×105 Force=1.01×105×4×∏×0.252≈80000N Actual answer 20000N...

So, when you generate electricity, you spin a magnet pushing the electrons in the surrounding wires and creating a stream of electrons, now the confusion... If you do this for some time, wouldn't the electrons in the wires run out? I mean there is only a certain number of loose electrons on the...

Hello all, i have an equation for flux density taking the inductor chrecteristics into account as Bmax= (Vrms * 10^8)/(4.44*A*N*f) but the company i work for has given it at Bmax=(Vl * 10^4)/(4.44*A*N*Vss) where Vl = voltage across inductor. i am finding a lot of variation for...

Quantum Confusion -- "Does not exist until it's observed" and age of universe Hi. I ran across this: http://physics.jamesbaugh.com/quanta.html QUOTE: "It is a problem of assuming values of properties are "out there" independently of the acts by which the values are determined. The...

Hi, So I have a circular linked list; each element of the list has a int value and a next pointer to the next element. BUT. When I try to compare rather the NEXT element has a certain value, I always get a true return; how do I properly compare the structure values with an int? I'm doing...

Could you please help me to understand some basic concepts about antenna polarization. The books I have are really confusing and do not have examples that I can learn from. Please look at the attached E plane radiation pattern image I attached (figure 13). The books image (figure 13)...

Apparently for emf to be induced in a coil, the magnetic field (or part of it) has to act along the normal to the coil face. So does this mean that the coil moves side-ways through the magnetic field? where instead of moving through its length (its longer side), it moves through the coil face...

This is from a textbook but it is not a homework problem, it's an example following the introduction of the "Sandwich Theorem". It says "for all x ≠ 0", but then it appears to assume that x = 0 when it finds the limits of g(x) and h(x). Clearly 1 ≤ u(x) ≤ 1 means u(x) = 1, I don't dispute...

I understand that they have done \displaystyle\sum_{r=k-1}^{2k} r =\sum_{r=1}^{2k}r - \sum_{r=1}^{k-1-1}r But where did r = 1 come from as r = k-1 before is what I don't understand. Also this question: Show that \displaystyle\sum_{p=3}^{n}(4p+5) = (2n+11)(n-2) \displaystyle4\sum_{p=1}^{n}p...

Well, am an Alevel student... Edexcel.. I just find quantum physics a really really confusing topic.. My question is particularly in black bodies. If we consider the sun as a black body, where did the radiations of the sun initially come from. I don't mean the emitted radiation we see, i mean...

Hi, Please apologize the ignorant question, but I am confused on applying the discharge capacity of a capacitor. If Farads = Coulombs/Volt, then a hypothetical 1 Farad capacitor could generate 1 volt at 1 amp for one second. But by the same formula, a .00005 Farad capacitor could generate...

Transition in LS-coupling confusion ! :) Hello :) Lets take for example a 2 electron system with l1,s1 and l2,s2. One electron changes energy due to electric dipole. I understand the rules for electrons in electric dipole transitions: 1) Δl = +/- 1 (parity flips) 2)...

Dear all, I have a confusion about partial derivatives. Say I have a function as y=f(x,t) and we know that x=g(t) 1. Does it make sense to talk about partial derivatives like \frac{\partial y}{\partial x} and \frac{\partial y}{\partial t} ? I doubt, because the definition of...

line integral -- confusion on squares and square root terms Homework Statement Do you see where they have sqrt(16 sin^2t etc = 5? How do they get that, the answer should be 7, the square root of 16 is 4, sin^2 + cos^2 is 1 and the square root of 9 is 3, 3 + 4 = 7. It's like they're...

Reading Brian Cox and Jeff Forshaw's book "Why does E=MC2". They mention that satellites speed up with time, but, then reading Wiki it says the crew of the ISS experience the slowing of time. Which one is correct? I'm slightly confused. Both experience a weaker gravitational pull and high...

My lecture notes say: Let f:[a,b]->R be bounded. F is said to rienmann integrable if: L=\int_{a}^{b} f(x)=U where : L=Sup(L(f,P)) and U=Inf(U,(f,P)) but everywhere else(internet) there's a definition with epsilon. I have the epsilon stuff later under "riemann...

Microwaves heating is often referred to as dielectric heating, but I'm not sure why this seems so special to specify of all the different thermal radiation frequencies. Doesn't infrared heat the dielectric material as well in a similar process? Isn't radiation heat transfer common for a wide...

I'm struggling with Bayes' theory. Please consider the following: Example 1: Submarine sinks if one missile hits it. Two ships aim at submarine and fire one missile each. Ship 1 shoots missile X1, ship 2 shoots missile X2. P(X1 hitting = 0.8) P(X2 hitting = 0.5) P(X1 and X2 hitting | submarine...

Homework Statement a) Evaluate the work done by the force field F(x, y) = (3y^(2) + x)i + 4x^(3)j over the curve r(t) = e^(t)i + e^(3t)j, tε[0, ln(2)]. b) Using Green’s theorem, find the area enclosed by the curve r(t) and the segment that joins the points (1, 1) and (2, 8). c) Find the...

I have a question about the Unruh effect. For the spacetime to be flat, it must contain no energy. But the Rindler observer is supposed to be eternally accelerating, which would require infinite energy. Is there an obvious resolution to this apparent contradiction?

Homework Statement Compute the surface integral for F = [3x^2, y^22, 0] and S being a portion of the plane r(u,v)=[u,v,2u+3v], 0≤u≤2, −1≤v≤1.The Attempt at a Solution I managed to get the correct answer, because with some luck I defined the normal in the correct direction. I am just confused...

dE = dQ + dW = dQrev + dWrev = dQirev + dWirev. We have for an reversible process, dQrev = TdS and dWrev = -PdV. So; dE = TdS - PdV So this relation is for all changes (irreversible or reversible) since dS and dV are state functions. What doesn't make sense to me is the next part when...

Say a spring is on a horizontal table, and the particle is initially at the midpoint of the spring in equilibrium, and then the particle is displaced to one side. I have attached a diagram, let this side be more to A. Then I am confused as to which direction the tension in both sides of...

I'm reviewing for my final exam so one of the practice problems is: 5= 3^(x+5) Here's my attempt at it: ln 5= x+5 ln 3 ln 5 / ln 3 = x+5 (ln 5 / ln 3)-5= x 1.46-5 ≈ x -3.54 ≈ x I checked my answer and I get 3^1.46 ≈ 4.97 so rounding it up gives me 5 since I rounded off 1.46...

Suppose a function is defined as: f(x,y)=0 for x=y=0 Does this mean that the function would be zero when both x and y are xero or when either one of them are zero?

Hi all I have a confusion regarding a physics concept. When you consider area under graph (velocity time graph), if the area is below x axis, is the area considered to be negative? For example, look at the attachment. There are 2 shaded areas. Let the area above x-axis be A and area below...