Recent content by Dawei

Really? No one can do it? I wrote it simpler here: http://www.flickr.com/photos/54479402@N07/5047681891/

I'm trying to find the total charge on a conducting surface but am stuck at the last part of this integral. Maybe I'm just dumb but it looks really complex to me and I can't seem to figure it out. http://www.flickr.com/photos/54479402@N07/5045800952/#/photos/54479402@N07/5045800952/lightbox/...

Hello, I have taken 5 samples and found that my average concentration is 5 mg, with a range of .003 mg in either direction. I would like to calculate the variance with only this information. Is this possible? I am used to calculating the variance from the standard deviation, but I don't...

Thanks. That's what I tried to do (after your first post) but I got nervous, it didn't look like it was going to end up in the form that I wanted. I'll just multiply it out and see what I get though. All this time searching for a better way, I probably could have done it already. Thanks again.

Thank you...I'm still not getting what it should be though. I would like it to expand into the following form, and I'm having trouble figuring out the steps to get there: http://www.flickr.com/photos/41988307@N08/4928253310/sizes/l/in/photostream/

I know I probably learned this 10 years ago, but I really have no idea how to simplify something like this: (A*B + C*D + E*F)2 Is there any kind of shortcut (even a website that does it automatically!) that can help me solve expressions like this?

In this case it is density... By the way I'd also like to know the general answer here. That is, if the f0 term were a function of x as well.

I'm trying to simplify this. I have two functions, f0(z), and f'(t, x, y, z). One is the 'base' value that varies only with height, the other is the small 'perturbation' value that varies with all four variables. I am substituting these into an equation that calls for ∂(f)/∂(x) Do I write...

I'm an engineering major taking an advanced level physics class. I realize that I really have no clue when it comes to basic mathematics, and it is extremely frustrating. I always just learned *how* to solve equations, never what I was actually doing. For example the del operator. What...

I was reading this website, and I don't understand this last statement. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html It reads: "Since only a tiny fraction of the electrons in a metal are within the thermal energy kT of the Fermi energy, they are "frozen out" of the heat...

Yeah you're right. 10^9 was what I got when I took number of electrons / m^3 and raised it to the 1/3 power, to get N/L. I think I'm supposed to use the 1 dimensional equation. edit: yeah I was just being dumb, I had it right, was just using the wrong units for mass. Thanks though.

Homework Statement For free electrons in a metal, the depth of a potential well can be determined by observing that the work function is the energy required to remove an electron at the top of the occupied states from the metal; an electron in this state has the Fermi energy. Assuming...

The other reservoir, the hot one, does not have infinite heat capacity, it is maintaining a constant temperature because it is losing heat at the same rate that it is coming in from the refrigerator.

Hm, I guess it wasn't quite straightforward. It's just a simple refrigerator, pumping heat from a low temperature reservoir to a high temperature reservoir by inputting work W. The low temperature reservoir has infinite heat capacity, the high temperature reservoir does not. I'm trying to...

Hello, For a refrigerator, if a low temperature (TL) reservoir has infinite heat capacity, what is the heat QL that is coming from it? I have W = Qh - QL and I believe I know what Qh is, but I need a better way to express QL, something involving TL, TH, and/or W. I know QL = CpdT, but...