Pair Definition and 400 Threads

hi I always heard my lecturer mentioned about 'less than 1 exciton'. as everybody knows, exciton is electron-hole pair. can we have <<<1 exciton? What does it mean? thanks in advance for your reply.

Homework Statement find all orderde pairs of integers (x,y) such that x^2+y^2=4x+2y Homework Equations The Attempt at a Solution rearrange to--> x^2=4x+2y-y^2 because x and y can only be integers, y(2-y) must be divisible by x so y(2-y)>=x y(2-y)=x(x-4) x(x-4)>=x x-4>=1 x>=5...

Pair of moving charges -- confused Here was a subject I thought I kind of had a grasp on, but apparently my understanding of SR is not very good at all! We have 2 charges, a positive and a negative one. I'm holding one in each hand, and I'm running forward, so their attraction is...

I'm trying to figure out what the transconductance of a bipolar differential pair with a certain tail current would be, but I'm getting tangled up in thinking like "well the pair sees half the input swing, but the transconductance might be double if there are two transistors.."etc. Could...

There were two piers reaching over the Thames. On each pier I spied a different friend of mine, fishing. These two friends were born of the same mother on the same day of the same year, yet they are not twins. How is that possible?

This question was brought to mind while reading other threads. I didn't think it was appropriate to diverge those threads off their subjects, so I started a new one. (hope this is right). I'm specifically thinking about the extremely rare event of the interaction of two gamma rays as the...

So, let's get this straight :smile:. Black hole evaporation is, by the layman's version, supposedly due to a negative mass particle entering the black hole, while it's counterpart leaves, as radiation. These particles are formed near the black hole by vacuum fluctuations (i.e. pair...

A two-dimensional harmonic oscillator is associated with the group Su(2). What is that association? Solutions to the Dirac equation require a pair of spinors at each point? Can we think think of spacetime as having pairs of 2D harmonic oscillators at each point? Thanks for any help.

Homework Statement I am given a one form Psi = zdx -xydy and two vectors v(1,1,-2) and w(-2,1,1) both tangent vectors of R3 at point P(2,-1,0). I am asked to find dPsi(v,w). Homework Equations Lie bracket? The Attempt at a Solution I know how to computer Psi(v) at p but this...

Classify Cam-Follower pair in Cam-follower mechanism as...?? Hi guys... Just want to hear your views on the following case,I haven't reached any conclusion as of now... I think its better if mny ppl contribute their views abt this.. Here is the question:[Deals with Theory of Machines]...

It seems to me that the Ginzburg-Landau equations are derived from considering the particle of superconduction to be behaving in a superfluid way. This required the particle of superconduction to be a boson so that B-E statistics might apply. The use of Bose's presumptions surely tell us that...

When a photon, with the help of a nucleus experiences pair production to make a positron and an electron, the energy of the photon will equal the rest mass of both the electron and positron together right? Then when the electron and positron annihilate, the two photons produces will each have...

Effect of a pair of slip rings in a DC motor Hi, I have a question here. Knowingly that the effect of a slip ring in a DC motor is to reverse the direction of the current in a loop whenever the commutator changes contact from 1 brush to another, so as to ensure the loop to be always...

Homework Statement As in the title Why can an electron - antiproton pair not be created by a photon in free space? This question came up last term but our tutor told us that it is because there are "no stimuli", I'm sure there is a better answer than this. I seem to recall that it can...

In Pair Production where a high energy photon collides with a nucleus a positron and an electron may result. But I have also come across references that say that two high energy photons can collide with each other to produce an electron and a positron. Is this correct?

Apologies if this has been asnswered before or if it's in the wrong place but I really don't know the proper terms I should be looking for. I have a system whereby people are asked to choose between two items, then another two, etc. until all paired combinations from the list of items has...

Homework Statement i just have questions the one i couldn't figure it out the eletroc/position pair produce track drift chamber has field of 0.2 weber/m^2, radius of the drift 0.025m. using p = eBr equation to find the energy and wavelength of the pair producing photon. with the...

What holds a :smile::smile: pair together?

Why the decay of neutral pion to electron positon pair is forbidden?

I am trying to understand the cooper pair in a box. They don't seem to behave like normal particles. Can someone point me to a good intro. Especially on that focuses on how they are not like a quantum well. Some questions: 1) Does the cooper pair in the box see anything of the geometric shape...

Two consecutive positive decimal integers are such that the sum of the digits of each of them is divisible by 11. Determine the minimum possible pair of such numbers.

Does anyone could indicate what is the best literature to learn about black hole pair production? Any textbook explaining the instanton derivation in detail for the case of black holes? Jan

Hello, how do the angular distributions of Bhabha Scattering e^+ e^- \Rightarrow e^+ e^- and Muon pair production e+ e- \Rightarrow \mu^+ \mu^- differ? Regards, Phileas Fogg

Say we have two electrons in a spin entangled state about the z-axis |01> + |10>. One electron travels off to our left, the other to our right. The right electron passes through an inhomogeneous magnetic field with gradient solely in the z direction (Stern-Gerlach type), and subsequently...

Hello, Im trying to find out if, since an electron positron pair can anhillate to produce a muon-anti muon pair by the weak interaction, can the same thing occur for the production of an electron/anti-electron pair? Or would it just happen by the electromagnetic force? Or both, with the weak...

A bit confused about how it works. Link - http://www.technologystudent.com/elec1/transis2.htm (3rd fig from top) The way I understand, transistor TR1's Base-emitter conducts, which fwd biases B-E junction of TR2. This in turn will turn on the lamp, but it won't be really bright. Once its...

I was just wondering how you might use Lewis theory to predict the reaction of molecules with an incomplete octet with a molecule that contains a lone pair? The idea is very abstract to me, I'd appreciate any ideas.

Hi guys I hope you can help. The other day I tried to explain to someone the mechanism behind 'stripes' in lightly doped cuprates that gives rise to the Mott insulator/ anti-ferromagnetic stuff. It quickly became clear that my understanding of super-conductivity differs considerably from the...

Homework Statement I have 2 questions from a practice test paper that I can't do (I missed the lessons) - I've attached them, the other questions I did fine. They should be quite basic but I'm not sure if what I'm doing is right (only done physics for 2 weeks). If anyone could correct my...

Homework Statement the 1.0kg block is tied to the wall with a rope. it sits on top of the 2.9kg block. the lower block si pulled to the right with a tension force of 20N. the coefficient of kinetic friction at both the lower and upper surfaces of the 2kg block is mk=.40. what is the tension in...

Hi! I have encountered many differential crossections: \frac{d\sigma}{dE_+d\Omega _+ d \Omega _-} (Pair production of electrons and positrons) Where E+ is energy of positron. However, in all of these crossections, the energy of the electron; E- is included in the formula, e.g eq 2.1.1...

Hi I am looking for a source which covers a differential crossection for pair production of electrons and positrons due to photons. \frac{d^2\sigma}{dEd\Omega} I need it to be valid for high relativistic energies of electrons/positrons and for all angels. I can only find formulas...

Homework Statement A pair of fair dice is rolled until the first 8 appears. What is the probability that a sum of 7 does not precede a sum of 8. Homework Equations Geometric series The Attempt at a Solution P(sum of 7 does not appear before sum of 8) = 5/36 + 5/36 * 25/36 +...

5. A photon of energy E strikes an electron at rest and undergoes pair production, producing a positron and an electron: photon + e * = e * + Positron + e * The two electrons and the positron move off with identical momenta in the direct ion of the init ial photon. Find the kinet ic...

I'm a little unsure about a certain part of this shown in a book. There is an electron and a positron moving in the +x direction. They annihilate each other and release 2 photons. to conserve momentum 1 moves in the -x and one in the +x direction. So then the first step is to do conservation...

I read about "pair production" how a photon can create and electron and a positron. I read the calculations and I understand how this is impossible unless something else (a nucleus) is present to take away some of the initial photon momentum, however, the book doesn't say exactly 'how' the...

Dirac's theory of the electron predicted that there were identical particles of equal mass but of negative energy. He appealed to the Pauli exclusion principle and proposed that there was a negative energy 'sea' of electrons that was full up to -2mc^2 in order to answer critics that positive...

Use of the term "pair" vs "ordered pair" Why is it that authors use the term "pair" and "ordered pair" interchangeably and, maybe I'm mistaken, a little imprecisely? For example, in listing the field axioms, the language "for every pair x and y" is usually used. However, surly the author means...

Homework Statement assume that two dipoles are placed back -t0 - back along axis as shown: ((-) a (+))(( +) a (-)) ------------------x axisr is oriented between ))(( but above, a distance...

how do we define the eccenticity of a pair of straight lines

why can't a gamma ray photon -->positron+electron? My notes simply say this would violate momentum conservation (you need a recoiling nucleus), but why? I mean, the photon WOULD have momentum (=E/c), so the sum of momentums of the positron and electron would just have be E/c..

Hi everyone Thanks for taking the time to read my first post. I was reading Bill Bryson's A short history of nearly everything (which may be like saying that I was reading cat in the hat in an english literature forum, but i shall see). Unfortunately I don't have the book here, or i would make...

Homework Statement To show that the minimum energy a photon must have to create an electron-positron pair in the presence of a stationary nucleus of mass M is 2mc^2[1 + (m/M)], m is the electron rest mass. Homework Equations Conservation of energy and momentum.Also the minimum energy a...

Say we have a BELL state |B00> = cos(a) |00>+ sin(a) |11> then for a (just one) pair of entangled particles, we keep one on location q, the other one in location w; the one in q forms a system Q, the one in w forms W. ( 'x' in a function like |v> x |w> indicates a tensor product)...

[SOLVED] Constructive and destructive interefernec and a pair of speakers Homework Statement Two loudspeakers, A and B, are driven by the same amplifier and emit sinusoidal waves in phase. Speaker B is 2.00 m to the right of speaker A. Consider point Q along the extension of the line...

Homework Statement Prove ln(1+x)>=(x)/Sqrt(1+x) Prove (x-1)^2>=x((ln(x))^2) For x>0 Homework Equations The Attempt at a Solution I have tried using MVT, but i only end up with more inequalities that i cannot seem to prove... Another idea that works but i cannot prove exactly...

Why is the nn-pair unbound? I don't seem to find the answer in any of my textbooks =/

Homework Statement Is it possible for pair production to occur without interacting mwith matter? Homework Equations E+ + E- = E(gamma) - 2*m_e*c^2 The Attempt at a Solution In the Coulomb field of nucleus (or electron), the incident photon energy can be converted to the...

Homework Statement Show that the creation of an electron-positron pair (or any particle-antiparticle pair, for that matter) by a single photon is not possible in isolation, ie, that additional mass (or radiation) must be present. (Hint: Consider the reaction at threshold, then apply...

which pair of elements is most apt to form an ionic compound with each other? nitrogen and hydrogen or barium and bromine? please explain