Recent content by johnnyies

Homework Statement from the cartesian definition of angular momentum, derive the operator for the z component in polar coordinates L_z = -ih[x(d/dy) - y(d/dx)] to L_z = -ih(d/dθ) Homework Equations x = rcosθ y = rsinθ r^2 = x^2 + y^2 r = (x^2 + y^2)^1/2 The Attempt at...

Homework Statement Estimate the energy density between 499.5 and 499.6 nm emitted by a blackbody at a temperature of 2000 K. Compare to the classical value predicted by the Rayleigh-Jeans law. Homework Equations http://en.wikipedia.org/wiki/Planck%27s_law The Attempt at a Solution now I...

Homework Statement I just took an exam and one of the questions gave us a finite line of charge and asked us to calculate the E-field at a point at a point P to the right of the line of charge. here is a poor sketch [+][+][+][+][+][+][+][+][+][+][+][+]---------------------------------- .P...

umm, since he was willing to offer $1200, maybe he wants the original printing. Anyways, what's so valuable about the first one? Did Richard Feynman sign all of them?

easy as calc 1

I've read that companies who remove chairs from board meetings get better results from them. So it has something to do with standing up.

Hey, has anyone ever seen a clearboard? What kind of pens do you use on a clear board? img: http://t0.gstatic.com/images?q=tbn:JP-wFtJJxBaDtM:http://i18.photobucket.com/albums/b130/Jelsemium/Numb3rs/93431_ptv_0047r225.jpg&t=1

I use a chalkboard cause it was given to me for free. But yes, they are pretty handy for studying. As a plus, you aren't sitting on your bum the entire time. I couldn't stand the smell of dry-erase markers anyways.

I don't still understand how assuming P, then proving Q shows that P \rightarrow Q is true?

Ya, you're right; that's the question though. The book told me to refer to a proof strategy in which you have givens, and the statement you want to prove is P \rightarrow Q in which you assume P as a given, and prove Q. Which is similar to what you're saying?

Crap. I accidentally clicked submit instead of preview post. Attempt at solution: Our two givens for this proof is that x is a real numberand x is not 4, and the statement is in an if P, then Q: P \rightarrow Q. However, the proof is in the form of the converse, if Q, then P: Q \rightarrow P...

Homework Statement Theorem. Suppose x is a real number and x \neq 4. If \frac{2x - 5}{x - 4} = 3 then x = 7 What's wrong with the following proof of the theorem? Proof. Suppose x = 7. Then \frac{2x - 5}{x - 4} = \frac{2(7) - 5}{7 - 4} = \frac{9}{3} = 3. Therefore if \frac{2x - 5}{x - 4}...

I have chalkboards and whiteboards. I stand up when I study.

What's the starting salary for a physics/math major at Wall Street? I doubt any salary will be enough to live in New York. College grads are fleeing that state because of the high cost of living. Probably should 'risk' it with academia.

There's there's a lot of mentions of saying that you should go for a more lucrative degree, and in your free time, you can do your own studying/research. While it seems logical, wouldn't that take time out of other things you can enjoy in life. . . family and friends? Doesn't seem so practical.