Recent content by poonintoon

Thank you, yes you have understood me correctly! That is my question. I thought that 6!/(2!3!) was basically equivalent to finding distinct permutations of ABCDEE (which would include ABE etc but clearly not). What does 6!/(2!3!) tell you the number of?

Homework Statement Find the number of distinct three letter words obtainable from the letters A,B,C,D,E in which E may occur 0, 1 or 2 times but the rest may occur only once. Homework Equations Number of combinations when picking r objects from n possibly objects in which one object is repeated...

Hello, I am looking for a physics/engineering project that is doable over a couple of weeks and has a bit of wow factor. Building a trebuchet would be a good example but I would like to do something else. Any ideas? Thanks.

Why is sound louder in a room with many people? Thanks

Please could somebody explain how the coefficient of static friction can be quoted as a constant in tables etc? \mu_s = F_s/ R In most cases the reaction force is constant but as I push the box harder the friction force increases. Is \mu_s actually the coefficient of limiting friction? Or...

MIT has a Physics Demo called "Rubber and Glass Rods with Tinsel and Balloon" (Not sure if I can post links but easily found on youtube). I have watched the video several times but am a bit puzzled. First the lab technician charges the rod by friction but then when he moves it close to the...

Hey, could I pester you again? I am still banging my head against the wall with this question. I have \int_{0}^{2\pi} d\phi \int_{0}^{\pi} d\theta \int_{0}^{\infty} dr \, r \sin(\theta)...

Doesn't the \vec{b}.\vec{r} term then become a horrible mess though? Like b_{1}cos\theta sin \phi +b_{2}sin\theta sin \phi+... which is a pain because it is in the exponential so at best you can get it in the denominator of a fraction when you integrate r out.

Hi, Thanks, you are right about the pi factor. But what if the function f(x) was say x then there would not be a pole and residue calculus wouldn't make sense would it?

Hopefully people are still prowling the forums this close to christmas :) I want to show that sin(ax)/x is a representation of a delta function in the limit a->infinty i.e 1) It equals 0 unless x=0 2) integrated from plus minus infinity it equals 1 and 3) multiplying by an arbitrary...

Hi, I am trying to show that for two operators S and P: (S+P)^{-1}=S^{-1}-S^{-1}P(S+P)^{-1} I can't get anywhere and searching on google I am not even sure if it is possible to solve the general case but the question gives no more hints. Any help appreciated. Thanks. J.

Hi I am looking at Quantum Computation by Neilsen and Chuang at the CHSH inequality. Looking at the spin singlet state they make measurements of for example the observable Z1 and Z2-X1 and then find the expectation value of the product. I am slightly confused here because a) Z and X are...

Thanks that's what I wanted, I thought once I had seen this I would be able to figure it out, unfortunately it's just not clicking for me. Can I check I have the right thinking... \epsilon_{ijk}\partial_j A_k For B1 you set i to 1. then that leaves two combinations for partial_j A_k...

It is, but I can't find out how to use it.

Hi, does anyone know a link showing how to calculate curl with a Levi-Civita tensor. I can't figure it out but I am sure if I could see an actual example would be able to work out what is going on. Thanks.