# Search results

1. ### A question about ballistics

Air resistance will play a role in how far the projectile lands, however, if it did have a significant effect, I would think the bigger cannon ball would be impacted more than the smaller bullet (assuming that there shapes are similar). I don't recall that air resistance has a significant...
2. ### A question about ballistics

The actual distance a projectile (bullet, cannonball, etc) travels will depend on the angle at which it is fired. As long as the gravitational forces do not change, mass has no play into determining where and in what time the projectile lands. It can be shown that in order to maximize the...
3. ### Cohesive energy calculation

I would find the factor of 2 to be normal as it is cancelled out by the 1/2. The purpose of 1/2 is to eliminate the double counting. This is typical for pair interaction potentials. If you're comparing with the book, there is a possibility of a typo.
4. ### Cohesive energy calculation

Best to express the term in brackets (where the sigmas and R's are in) as something like U_ij and then manually perform a double sum and collect like terms. You should see the N pop out. Note that for this to work U_ij = U_ji as you stated.
5. ### Average of function (using dirac delta function)

From the problem statement, your a is = to 1 not -1.
6. ### Drawing crystal structure software

By draw, I think you mean visualization. Ovito or AtomEye should do the trick. They are free software used by research scientists. You can find them through google.
7. ### Varying The Gibbons-Hawking Term

I would suggest expanding the summation over mu and nu and then applying the variation operator.

I would not worry to much about the CC transcript. Admissions to Ph.D. programs look at other things besides the transcripts such as letters of recommendations, research and work experience, GRE test scores and your letter of intent (that being a written letter by you on why you want to attend...
9. ### Triboelectric generators

BTW triboelectricity is not piezoelectricity. Piezoelectricity uses crystal like materials to generate power when they are subjected to stress, where as triboelectricity uses materials that are brought into contact to generate power.
10. ### Triboelectric generators

Energy Density = Power/Area. It is a metric that describes how good a power technology is. If you have 98 Watts/Square meter and you had 1 square meter of triboelectric material, you should expect 98 Watts of power. Or if you have 2 square meters of triboelectric material, you should expect 98 X...
11. ### How to find equipotential surface for given case?

I can answer the second question. At far off distances the grid should look like a uniformly charged plane. This results in the potential being equivalent to that of a uniformly charged plane.
12. ### Triboelectric generators

Triboelectricity happens as a result of taking two different materials and rubbing them together. After rubbing, one material gives up its electrons to the other material. This results in one material becoming negatively charged and the other becoming positively charged. When you separate the...
13. ### Faraday's vs Ampere's Laws and current density

On the right side of Del X E you would have the negative of the time derivative of B. The substitution for E looks fine.
14. ### Force between wires

May I suggest you first figure the magnetic field (or magnetic flux density) on each wire due to the other wire. The magnetic field can be obtained using Amps Law. From the magnetic field you can then obtain the magnetic force which in this case is given by F=I*L*B where I is current, L is the...
15. ### Engineering Physics or engineering for study?

If you want to do pure research or teach Physics, then Physics is the way to go. If you want to design and build things, then Engineering is the way to go. For Physics, I'll have to caution you that if you want to conduct pure research in Physics, you will need a Ph.D. Not to say you cannot get...
16. ### Is it possible to produce the inverse of a decay?

Yes, though I would not call that inverse decay. Fusion might be a more appropriate term and their would be release of energy.If you look at the nuclear binding energy curve, you'll see that low Z elements are most likely to undergo fusion, where as heavier elements are likely to undergo decay.
17. ### Equations of state -- Partial derivatives & Expansivity

May I suggest you use the chain rule of derivatives since V=1/rho=(rho)^-1. Take the derivative of the outside function times the derivative of the inside.
18. ### MQF or PhD physics? Decision for Fall 2015

I have a degree in Physics and yes you can transition from Physics to finance like positions because I have made that transition. When I started out my career I was a Research Scientist for the Army (on the government side, not a contractor) conducting research on Power Generation Technologies...
19. ### DoD jobs and internships

I'm a government employee (GS level) who evaluates the cost and technical aspects of proposals submitted by companies like Raytheon, Lockheed, etc, so I have to cation, that if you want to work for these companies, know that you may not get overtime pay, unless it's a certain amount over. I...
20. ### Fourier series, Hermitian operators

Sorry the square of the momentum operator is -(hbar)^2*d^2/dx^2
21. ### Fourier series, Hermitian operators

I believe the point of your problem is to prove that d^2/dx^2 is Hermitian. You only need to substitute and show that the difference <f|Lg> - <Lf|g> is zero using integrals. All functions in quantum physics should be square integrable because if they weren't, then the inner product, and hence...
22. ### Quantum state of system before measurement

The statement you can make about a wave function before measurement is that it is a superposition or sum of basis wave functions, such that when a measurement is made, that wave function collapses into one of the basis. Another words it is a wave packet made of many waves each with its own...