# Search results

1. ### Support PF: Buy on Amazon.com from here

Wow, never knew about this until the mass email about the login issues. ...and I just bought ~\$200 of books from amazon 2 weeks back. Dang.
2. ### Mathematica Solve large equation (Mathematica)

Perhaps nice compact solutions simply don't exist if your expressions are too complicated. Do you really require an algebraic expression? If not, plug in your expressions for w and v, then use Solve/NSolve.
3. ### Number of C-14 atoms in old piece of wood

Well....*technically* N(t1) = N_0 * e^{-\lambda*t1} , so you shouldn't have cancelled out the N0, although it does not affect your final answer.
4. ### Organic cis- tran- structure

We use the terms cis-but-2-ene (best be clear where the double bond is) and trans-but-2-ene in my chem classes, so I think they're fine.
5. ### Classical or quantum electromagnetic theory?

In no way does the classical theory imply that the statement is false. As said above, quantum and classical theory do not disagree on the definition of the word "intensity".
6. ### Simple Electrostatics Lab: Clarification

Hm, maybe the discharging effect of you touching it is not that significant after all...>.<
7. ### Simple Electrostatics Lab: Clarification

You have to charge both combs separately, then bring them together to see if they attract or repel.
8. ### Simple Electrostatics Lab: Clarification

Both the object and the comb will be charged. What you really want is the comb to be charged, not the objects!
9. ### Electric Field Zero where?

They're really pretty much the same thing isn't it? If L is unknown you will have to give your answer in terms of L anyway.
10. ### Simple Electrostatics Lab: Clarification

That's because you shouldn't be touching the charged comb. If you do, you'll act as an earth and the comb will be discharged. As for the other materials, it's for you to try and find out =D
11. ### One dimensional motion problems

1) Can you find the displacement (with respect to the flagpole) of each runner at any given time? When they meet, what must their displacement be? 2) How long does it take for the train to stop with the given acceleration? Thus how far would it have travelled?
12. ### Simple Electrostatics Lab: Clarification

The purpose of the second comb is to find out the polarity of the charges! You have no way of knowing if you're using just a single comb. You shouldn't expect to find them charged in their natural state.
13. ### Electric Field Zero where?

Yes, it should be wanting 2.90.
14. ### Electric Field Zero where?

What are the coordinates of q1 and q2? Therefore what is the coordinate of the point with zero E field?
15. ### Electric Field Zero where?

You ought to count from the origin...
16. ### Raman effect and fluorescence

If the photon is absorbed, it is completely absorbed, since its energy will match the gap between the energy levels of the atom. When the atom falls back to the ground state, it might not do so in one step, but instead it might have several transition states. If so, at each transition, the...
17. ### Partical equilibrium

"-1/d^2 = 11/(d+L)^2 where L = sqrt(125)" L should be sqrt(1.25)... Simply cross multiply, expand the brackets, and solve the quadratic equation!
18. ### Electric Field Zero where?

Yes, since you assumed L = 1, x=-.395 will be between the two charges.
19. ### Simple Electrostatics Lab: Clarification

When you rub against the comb, you don't know if it gains a positive or negative charge, right? Thus you rub one comb with, say, cotton, and the other with rubber. If the combs attract, they have opposite charges.
20. ### Complex Roots

If you draw it out on an Argand idagram, the argument is - tan^{-1} \sqrt{3} = -\frac{\pi}{3} so z^4 = 2e^{(-\frac{\pi}{3} + 2n\pi)}
21. ### Classical or quantum electromagnetic theory?

Indeed the energy densities are the same precisely because the intensities are the same! The original sentence is false. The third paragraph you quoted does not imply in any sense that the statement is true, does it?
22. ### Complex Roots

express the right hand side in the polar form: |r| e^(x + 2*n*pi) then you can take roots on both sides explicity and solve from there.
23. ### Products or Reactants ?

As mentioned before, this question is more than just acid-base equlibria. Take into account that Mg(OH)2 has a low Ksp as well, so consider its solubility equilibria. I'm not sure how they got that number, but you can imagine that it'll be huge. Any OH- produced will precipitate out, lowering...
24. ### Six more kinematics, worked out already with questions/doubts/wrong answers

1) Good point. Question should have stated "with respect to centre of the earth" to be more precise. Clearly in this case you've done what they wanted 2) Exactly the same thing as your other thread. Pay attention to the directions in your vector diagram! You have to swim against the flow to...
25. ### Electrostatic Problem - finding initial separation of two particles

You've written down the necessary equations to work out the potentials in your first post!
26. ### Classical or quantum electromagnetic theory?

If the intensity is the same, and the beam sizes the same, the energy carried by each is the same... Besides, even going by classical theory, how can you assume that energy densities of the two different beams are the same? "According to this view, the intensities of radiation are equal...
27. ### Six kinematics problems - all either worked out with wrong answer or conceptual

2) The time taken to cross the river would be the width of the river divided by the velocity component in that direction, right? The velocity component parallel to the river doesn't matter here as it doesn't contribute to getting you across the river. 3) Eh, 3 choices are arrows, the 4th is a...
28. ### Vector Identity Rules Ax(BxC)

No it wouldn't, I wonder what makes you think so?
29. ### Vector Identity Rules Ax(BxC)

Which identity are you referring to? Whatever the identity it would work for any vector....but of course the cross product of 2 equal vectors is zero =)
30. ### EM field between 2 superimpose spheres

As stated, you will need Gauss's Law. Go wiki it. You ought to get a text though, cliff notes are horrible for learning.