# Search results

1. ### The relationship between the lattice spacing and the distance between parallel planes

I found the solution had already been posted here: https://www.physicsforums.com/showthread.php?t=119037 Can someone explain why the sum of the squares of the cosines is equal to one though? It just says 'from trig' but I'm not familiar with that identity :/
2. ### The relationship between the lattice spacing and the distance between parallel planes

How can one derive the relationship for a cubic crystal: d= \frac{a}{\sqrt{h^2 + k^2 + l^2}} It is shown here. This is probably trivial but I am having trouble proving it as the Miller indices are reciprocals but the reciprocal is not distributive. This isn't for homework by the way - I...
3. ### Where can I find theoretical isochrones?

I found the data here http://stev.oapd.inaf.it/cgi-bin/cmd it is rather laborious to strip the data calculate the relevant colour index and plot it so I might make a python script to do it. I hope this will be of use to anyone else who has the same problem and comes across this thread via the...
4. ### Where can I find theoretical isochrones?

I am currently doing a 2nd year lab report and need some theoretical isochrones to work out the age of some clusters, M15 and H+chi persei (Double Cluster). I was going to use Seiss: http://www-astro.ulb.ac.be/~siess/server/iso.html [Broken] But it doesn't seem to be online :( What...
5. ### The treatment of errors and uncertainties?

Thank you!!! This finally made me understand that confusion I had. Now it all makes sense, I think so far in my experiments I am justified in assuming uncorrelated (i.e. independent errors) and so therefore need not worry about covariance.
6. ### The treatment of errors and uncertainties?

I am confused over how to work with errors and uncertainties. So far when dealing with a small number of measurements I have used the partial derivative method to calculate the final error in my result e.g. if my result is E=mgh \text{ then assuming no error in g my uncertainty is }...
7. ### Programs How easy is it to find funding to do an Applied Physics PhD abroad?

Those look interesting, I'll see what research is available at my university too as it'd be cool to get to know the staff well before third and fourth year where there is more research done (that's a horrible sentence but you see what I mean :P ) I'll try and apply for IAESTE too but that...
8. ### Programs How easy is it to find funding to do an Applied Physics PhD abroad?

I got a 1st (87%) in the First Year and am just entering the second, that got me on the Deans Commendation thingy which is like ~40 students out of each year or something. I also receive a scholarship from the university due to getting 5As at A level from a struggling school (if only they had...
9. ### Programs How easy is it to find funding to do an Applied Physics PhD abroad?

Although I am not yet sure which area I would want to do a PhD in (I am only in 2nd year undergrad) it would most likely be something applied like accelerator physics, plasma physics, metamaterials, plasmonics etc. (I realise this is a ridiculous range of topics :P ) The proposed ~30% cuts to...
10. ### Hey, guys and gals, it's vanity time!

Panda eyes, yay! Apparently as a male, I look like Edward Norton. As much as I wish that were the case, I don't really see it myself :P
11. ### Please explain what a Fourier transform is?

Hmm, I noticed that the period goes to infinity and thus the discrete summation becomes a continuous integral, but what does that actually mean? I mean what is it that the Fourier transform actually tells us, what is it used for? I understand the usefulness of being able to approximate functions...
12. ### Please explain what a Fourier transform is?

I understand Fourier Series fairly well and how to use them to approximate functions (I even wrote a C program to do it) but Transforms are really confusing. If I was to take the value of each fourier coefficient and plot it on the y-axis against the angular frequency on x-axis (obv. there...
13. ### Physics Making it as a physicist

Indeed, as Newton said "If I have seen further it is only by standing on the shoulders of giants." and was it E.O Wilson who said "Genius is the hard work of many attributed to the names of a few for convenience." Evolution or transmutation as it was known before, was understood to have...
14. ### Faraday's Law

Yeah, that seems correct as you are just using the definition of flux: \phi = \int \vec{B} \cdot \vec{dA} And subbing that into your above expression for the emf. It looks correct but I'm not certain as I'm only a mere first year so you should probably get someone else to confirm.
15. ### Best foreign language for Future Physicist

French perhaps as ITER is at Cadarache no? And the EPFL is French-Speaking, thus the name. But English is probably sufficient. It would be awesome to one day work in Fusion, I just hope I do well enough now in undergrad to get a PhD and so forth. Good luck :)
16. ### Thermodynamics (Adiabatic PV Diagram)

Homework Statement Give a definition of an adiabatic process. Derive an expression for the work performed by n mol of an ideal gas undergoing an adiabatic expansion in terms of the initial and the final temperature of the gas. [Hint: you may find it helpful to apply the First Law to the...
17. ### Simple vectors question that I can't seem to get right?

True, but I'd already typed it up there. It seems like the mark scheme might just be wrong as everyone else seems to get the same answer as me.
18. ### Simple vectors question that I can't seem to get right?

All information pertaining to the question and my attempted solution is here: http://mathbin.net/39295 [Broken]
19. ### Repulsive Casimir Forces

I need to do a basic talk for a few minutes on Casimir forces and their effects on nanotechnology. I kind of understand the basic concept of Casimir forces intuitively, as less virtual particles can exist in the standing wave state between the plates than can exist outside of the plates and...
20. ### Capillary rise-conceptual

I'm guessing here too, but I'd imagine it'd rise to the top of the tube, as the molecular forces responsible for the surface tension are still present, but the water has no effective weight as the lift is in free fall, therefore there will be a net upward force which will pull the water up the tube.
21. ### Energy-Time Uncertainty Problem.

Hmm, now I realise if I use the partial derivative method for the treatment of errors I arrive at the same answer. \Delta v = \sqrt{ ( f \Delta \lambda )^2 + ( \Delta f \lambda)^2} = 0 \therefore f^2 \Delta \lambda ^2 = - \Delta f ^2 \lambda ^2 \therefore f \Delta \lambda = - \Delta f...
22. ### Energy-Time Uncertainty Problem.

ehild, I think your method is correct, I didn't realise you could express the uncertainty in the velocity as a sum like that, but that's awesome! Thank you for your help.
23. ### Energy-Time Uncertainty Problem.

Wait, surely one of derivations is wrong, and I have a feeling it is the one in terms of wavelength. The reason is because if I assume my working to be true, then we know that somehow we can equate the proportional uncertainty in frequency and wavelength. But from my workings thus far that would...
24. ### Energy-Time Uncertainty Problem.

Hmm... I've made a little more progress this time by starting with: \Delta t = \frac{\Delta \lambda}{v} = \frac{\Delta \lambda}{f \lambda} = t \frac{\Delta \lambda}{\lambda} Therefore \frac{\Delta t}{t} = \frac{\Delta \lambda}{\lambda} Which is very similar to my expression \frac{\Delta E}{E}...
25. ### Energy-Time Uncertainty Problem.

Yeah I mentioned trying to use E=\frac{hv}{\lambda} In my original post, I have been trying it for several hours now and still can't seem to make any progress, my main issue is that whilst something like \Delta E = h \Delta f is true, the similar statement, \Delta t = \frac{1}{\Delta f} is...
26. ### Energy-Time Uncertainty Problem.

c= f \lambda is only for photons though, whereas it says show that for ANY wave, so I guess that wouldn't be relevant. I could try using the frequency-period relation but I'm not sure exactly how.
27. ### Energy-Time Uncertainty Problem.

Homework Statement Following a question that asks for the Energy-Time uncertainty principle, \Delta E \Delta T \geq \frac{\hbar}{2} Show that for any wave, the fractional uncertainty in wavelength, \frac{\Delta \lambda}{\lambda} is the same in magnitude as the fractional uncertainty in...
28. ### Kind of a dumb question

Yeah, one of my professors was talking about this. The idea that it is mostly due to friction seems to be a popular misconception.
29. ### Simple Energy Levels confusion

So in general for atoms and molecules, do the energy levels get closer together as you move farther apart from the atom. That is, do the differences in energy between the energy levels decrease at higher energy levels?
30. ### Simple Energy Levels confusion

In the famous diagrams of the energy levels of a hydrogen atom it seems that the energy levels get closer together as they increase such that the difference in energy between higher energy levels is less than between lower ones. But working from the electron in a box approach we get the...