# Search results

1. ### Why are only some photons virtual?

Sorry it was hard to think of a good title. Essentially, why do only virtual photons carry the electromagnetic force? What stops 'normal' photons from carrying the EM force? Is it the fact that we can detect them? What decides whether a photon will be virtual and hence carry the EM force, or...
2. ### Why don't virtual particles cause decoherence?

I was recently told virtual particles don't cause decoherence. Why not? Do they just never interact with their environment (apart from transferring energy/force) so they can never collapse a wavefunction?
3. ### Why do things 'decohere'?

Could someone please explain why superpositions collapse when we observe particles? Surely if it is because we have interacted with the particle, then any interaction would decohere a particle, i.e. why would the magnetic fields in two electrodes (which are containing a particle) not collapsing...
4. ### Infinite Salesmen problem?

Hi, I'm looking into quantum computing, and if you could forgive my naivety I was wondering whether the superposition of a qubit could produce a one-step solution to an infinite salesman problem? The salesman problem is where a computer has to calculate the most efficient route for a man to...
5. ### Algebra without a calculator

How would one solve the following WITHOUT a calculator? Sub in t as x^{\frac{1}{2}} 4x+8=33x^{\frac{1}{2}} I just don't see how to do this without a calculator. If I take t^2=x, then sub it in I need to do the quadratic formula which is too hard without a calculator/would take too...
6. ### Superposition and Pauli's principle

Does Pauli's exclusion principle apply to superposition or only collapsed states? I.e. could a particle be 'superposed' - if that is the word in the same state as another electron in a localized region? Also doesn't Pauli's exclusion principle create a form of measurement because...
7. ### Is spin actually spin?

Hi, Just a quick question: When people talk about an atom's spin do they actually mean it is physically spinning or is it a word for some different process or property of the atom - if so, what property is this? Thank you for your time.
8. ### Electron Pump - Making

Hi, In the next week I am going to NPL for physics academy and I will be designing and building a prototype electron pump. I've tried to look for articles or books related to electron pumps or how to build them but I simply can't find anything at all. Does anyone have any material at...
9. ### What does 'observing' mean

Hi, Please can anyone tell me what 'observing' means for example when we 'observe' a particle its wavefunction collapses, however surely observation is the wrong word as human conscience has absolutely nothing to do with this. Any help is greatly appreciated, thank you
10. ### How can the Higgs Boson induce mass?

How can the Higgs boson induce mass? How can it interact with itself? Is it the only particle able to do so, if yes, why, and if no, what other particles can interact with themselves? As a side thought, is Young's Double Slit Experiment evidence of particles interacting with themselves (the...

12. ### Calculating gradient with distance and speed

Homework Statement http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_PC_2006_QP.pdf Question 11 Homework Equations h=v^2/g The Attempt at a Solution convert 36km/h into 10m/s 10 is final velocity so average should be 5m/s h=v^2/g=5^2/10=2.5m Using pythagoras...
13. ### Momentums, Ladder against a wall force

Homework Statement http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_PC_2008_QP.pdf Question 6 Homework Equations Moment = Force * Distance moved The Attempt at a Solution I have tried this and I am sorry to say that I have no idea how to work it out. I think it...
14. ### Force and acceleration leading to weight of a parachutist

Homework Statement http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_PC_2008_QP.pdf Question 8 Homework Equations f=ma The Attempt at a Solution Sure since f=ma A) would have force of 0, since there is no acceleration B) force would be 800N C) force of 0N D)...
15. ### Open switches, current

Homework Statement There is a circuit with 7 LEDS connected in parallel, each with a switch on its parallel. There is a battery supplied. The LEDS correspond to those of a digital clock for example the number 8 would light up all 7 LEDS, whilst the number 0 would light up 6 LEDS. Which...
16. ### Using a pendulum to find the distance to the sun

Hello, One or two years ago I had a mathematics lecture where one part of it was using basic formulae, a pendulum and the distance to the centre of the earth to find out what the distance to the sun was. Recently, I came across a question which asked me to figure out the distance to the...
17. ### Slowing down the speed of light in a medium

Hi, Before I phrase my question, I'll just go through what I know so no unnecessary comments happen. I've read that the speed of light slows down in a medium because when a photon hits an electron the electron absorbs the energy of the photon and re-emits another photon. I also know...