# Search results

1. ### Newtonian derivation of Scwarzchild radius

can anyone say why the derivation works? my teacher went through it in class and sort of said "don't question it" (which i hate) but it's still annoying me now even though it's a few weeks since i finished college. KE = GPE 0.5mv² = GMm/r r=2GM/v² and then if the escape velocity is the...

Hi, I'm 18 and have just completed my A levels. I will be studying physical natural sciences at uni if I've got the grades in my a levels (I'm pretty sure I have) I would like to volunteer teaching high school level maths and/or physics in quite a deprived country (somewhere in Africa...
3. ### Revising simple lenses - magnified, and diminished images

Basically, I'm trying to revise lenses and the one thing I never really understood was how to tell whether an image is magnified or diminished. http://store.aqa.org.uk/qual/gce/pdf/AQA-2450-W-TRB-OGA.PDF pages 6 and 7 has the diagrams to show what I mean I can do the geometry of an object...
4. ### Proof that the sum of a number's digits is a multiple of 9 iff it is divisible by 9

Homework Statement prove that the sum of a number's digits is a multiple of 9 if and only if it is divisible by 9 Homework Equations none that i can think of The Attempt at a Solution say any real integer can be written as: anan-1...a2a1a0 where a0 is the units, a1 is the tens...
5. ### Eigenvectors - why must det(A-λI)=0?

if we say that an eigenvector u is a vector whose direction is unchanged by the matrix transformation A: Au=λu=λIu rearranging: Au - λIu = 0 u(A-λI)=0 we know the u=0 is obviously a solution. and i also appreciate that if A-λI=0 then A=λI which is just a scalar multiplied by the identity so is...
6. ### Summations using complex numbers

Homework Statement express in terms of n and r: \sum { ^{n} C _{r} } \times cos(rx) from r=0 up to n Homework Equations well i know de moivre's theorem also, in class we have been finding ways to represents a series of cosines added up as the sum of a geometric series so i tried it on this...
7. ### Vector grad as a normal vector

i have done a little on multivariable calculus in school -partial derivates and tangent planes to f(x,y), but now we have moved on to functions of more than 2 variables my teacher, however, doesnt really teach us - she gives us equations and tells us to do questions and i usually find myself...
8. ### Capacitors - energy stored vs work done

this isnt homework, im doing revision for an exam :) a 180 microfarad capacitor is charged so that is has a PD of 100v across the plates. i calculate the energy stored as 0.5cv² = 0.9J the question then asks me to calculate the work done by the battery in charging the capacitor. the mark...
9. ### Zero potential between two plates

Say there are two charged plates opposite each other, 1m apart; one is +20V and the other is -20V. There is a point where we say there is zero potential, 50cm from either plate. I don't understand how we can say that a charge would have zero potential when we define potential energy as an...
10. ### A simple rearranging question

Given: T=mgcos\theta and cos^2\theta + \frac{mV^2}{ag} cos\theta - 1 = 0 show that: T = \frac{mV^2}{2a} [1+\sqrt{1+(\frac{2ag}{V^2})^2}] I always get: T = - \frac{mV^2}{2a} [1 + \sqrt{1 + (\frac{2ag}{V^2})^2}] T represents a tension in a string so I understand why you'd take...
11. ### Uniform field between parallel plates

Hey, I've recently been studying electric fields, and our teacher told us that the field is approximately uniform between two charged parallel plates, ie the force acting on a unit charge is equal everywhere. This doesn't seem to tie with everything else we've been taught; surely, as you...
12. ### Programs Which of these UK degrees?

Okay, so I've applied for the following courses: Warwick - Maths and Physics Joint Honours - Offered AA Birmingham - Theoretical Physics - Offered AA Nottingham - Theoretical Physics - Offered AA/AB (Confirmed offer, but the exact details are being considered) Imperial College London -...
13. ### Recharging an electrochemical cell

If you want to recharge an elctrochemical cell, which electrode do you supply with more electrons? My thinking was: There was a P.D. between the elctrodes but now that the cell is spent, the P.D. is lower. To create a P.D. again, you must make the negative electrode more nagative or the...
14. ### Muon decay constant

muon decay constant/ muon flux where can i find the decay constant of a muon (the lambda which appears in): http://upload.wikimedia.org/math/3/f/2/3f28b1c0d4362b86a89f976d83d81070.png thanks edit: oh the wiki page http://en.wikipedia.org/wiki/Exponential_decay gives the relationship...
15. ### Relativity at cern - deflection

obviously an electron will change path when passing through a field could anyone point me to an equation which suggests how much electrons change path by - i guess it depends on mass, velocity (maybe in the form of momentum for the relativistic case im think of?), field strength and the...
16. ### Length contraction

http://cas.web.cern.ch/cas/Baden/PDF/Relativity.pdf on pg 16, it says that a muon travelling at a relativistic velocity towards earth would see the distance to earth shorted by the gamma factor... i thought the length of the muon is all that is shortened by the factor of gamma? am i wrong here? :s
17. ### Experimental data in relativity

hi, im doing a project on special relativity (im 17, doing A level maths, further maths and physics) for this project, I need to analyse some data. can anyone tell me where on earth you can find data from experiments which give empirical evidence of special relativity, like muons arriving...
18. ### Name of the experiment

i need the name of the experiment where you pass an electron through a p.d. and it accelerates, but as the electron's predicted acceleration (from field strength etc) would give a relativistic velocity, the results do not agree with newtonian mechanics? he said it's useful evidence, in a...
19. ### C being constant in all frames deduced backwards

Sorry, this is a really basic question which will possibly annoy you and I'm embarrassed to even be asking this :blushing: But if you travel at say 0.5c to the left (relative to your axes) and a photon of light goes past you to the right at c (again relative to your axes) what are the sums...
20. ### Programs Physics degrees in the UK and specialising at undergrad level

Hi, I'm going into my second year of 6th form and I've done: A level maths (did the "fast track" option) AS Physics AS Chemistry and I will be doing fast track A level Further Maths AS French (But I'm dropping that) So I'll leave with A level Maths, Further Maths, Physics and Chemistry...
21. ### Velocity and mass?

Sorry, I'm very new to this topic, this is going to annoy you I expect. How do we define velocity in relativity? There's no fixed aether to measure against. So in the lorentz transformation, when we say v2/c2... What does v mean? If we measure against a photon the photon will shoot past...
22. ### Graphical representation of complex roots to equations

I've never properly studied complex numbers but I will soon (in September). Basically: We get taught from a young age that: the real root of f(x)=x²-4 is where the graph of y=f(x) cuts the x axis But is there a graphical representation of a complex root? What's so special about the...
23. ### Deriving t=T/√(1-v²/c²)

On this page http://www.patent-invent.com/electricity/inventions/special_relativity_1.html [Broken] you are given that in a certain scenario -(cT)2 = (vt)2 - (ct)2 then it says Hence: t=\frac{T}{\sqrt{1-v^{2}/c^{2}}} But this doesn't rearrange to that equation, and I don't like taking...
24. ### Light clock moving to demonstrate time dilation

Hello all, having decided that I wish to apply to Oxford to study Physics (as well as Imperial and, I am still considering Natural Sciences at Cambridge), I have been informed that extra reading and independent study would be advised, so I'm delving into the world of relativity (I'm a first year...
25. ### Neutron-Neutrino collisions and the W bosons

Hi, I have my AS physics exam tomorrow and the only thing on the syllabus I'm unsure of is the reaction between a neutron and a neutrino and also the reaction between an antineutrino and a proton. A Ve is an antineutrino, I can't work the overline codes :/ I've seen various feynman...