1.

PS: h=9.5cm a=8.6cm

为啥不合适啊我觉得很合适

这件事告诉我们做事莫上头。。。。

如何提高英语水平？？？真心求教
@JZMPLPQ @ck_cookie

另求美利坚绩点，看到什么某球员GPA4.3，逆天啊，我国拿A才4.0啊

先召唤再出题..@ck_cookie @seepath @求助攻

Text assignment: By looking on the web, textbooks or other articles, explain the phenomenon of "triboluminescence", emphasizing the role of electrostatics. (You should use no more than one-third of a page.)
The following problems are to be done on paper, showing all work. The presentation should be neat, legible, and easy to follow.
What is the “self-energy” of the electron? (Don’t be scared by all the text – the calculation is not too difficult, though the result may be …unsettling.)
Calculation 1: Pretend the electron is made up of two halves, each with charge e/2. How much energy is required to bring the two halves together, i.e., so that they occupy the same point in space?
Calculation 2: That calculation was a bit over-simplified. Let’s do a better job. Pretend that the charge of an electron is spread uniformly over the surface of a spherical shell with radius r0. Next calculate the electric field everywhere in space, i.e., at an arbitrary distance r from the center of the shell. Obviously the answer will depend on r and r0. Next, calculate the total energy stored in the field, by integrating the energy density u over all space. Finally, let the “electron” become a point particle, by letting r0 go to zero.

召唤吧主失败了？
@ck_cookie