Remarks on AP courses in high school

[Lucretius]

48 hours have passed for me.
So DUDE, wait a sec.
The free-response... the ones I got were like super easy. The first one was like, measuring g and you had a table of d vs. t. The second one was on electricity I think. The third was on reflection/refraction and slit stuff. The fourth was on Thermodynamics. The mechanics question was somewhere in there and one on an electron and a positron and stuff.
If that's the paper you had, I seriously think you were mistaken if you thought it was difficult and the multiple choice was easy... 'cause... well... the multiple choice pretty much raped me. :(

You got Form B of the free-response questions, from your description. I didn't have any sort of table for section 1. Was this the test you had? Here is the test I took. I didn't think the multiple choice was very hard; the practice multiple choice exams I had taken in class were much more difficult than this years'.

Look at question 3 on my free response section and see if you can tell what they wanted there. I left that whole page blank.

 

[jbusc]

You got Form B of the free-response questions, from your description. I didn't have any sort of table for section 1. Was this the test you had? Here is the test I took. I didn't think the multiple choice was very hard; the practice multiple choice exams I had taken in class were much more difficult than this years'.

Look at question 3 on my free response section and see if you can tell what they wanted there. I left that whole page blank.

on question #3, basically they are asking questions about the electric field generated by those two point charges. Each point charge has an electric field associated with it; the total electric field is the sum of the two fields. Given the charge on one point, you can calculate its contribution to the field; since you know the total field at that point is zero, then you can calculate the field due to the other point and from that calculate the charge.

 

[Pseudo Statistic]

You got Form B of the free-response questions, from your description. I didn't have any sort of table for section 1. Was this the test you had? Here is the test I took. I didn't think the multiple choice was very hard; the practice multiple choice exams I had taken in class were much more difficult than this years'.

Look at question 3 on my free response section and see if you can tell what they wanted there. I left that whole page blank.

Yup, turns out I did have form B..
On the subject of tests on the website, they released the AP Physics C Mechanics test!
I mean... err... I have the test this Friday, and according to records there has never been an AP Physics C form B. I hope I get lucky. :D
So question 3 from your paper...
Since it says the net electric field at point P is zero, The electric field produced by q1 plus the electric field produced by q2 = 0... so, from there, you can plug in your known values and solve for q2.
Chances are, however, q2 is positive because since q1 is negative, a test charge 1C at point P would be attracted to it, (to the right), so it needs a positive charge, q2, to repel it to the left enough to keep the net electric field 0 at that point I guess.
For part c, the electric force on q2 would be the force on q2 caused by q1, Coulomb's law...
d... Electric potential would be 0 when
q1/4pi*e*d = q2/ 4pi*e*(0.3-d)
And solving for d.. (d would be the distance from q1 to the point)
e... I would integrate the coulomb force from infinity to the point, but I'm not sure if that's acceptable on physics B. You could say, instead, that it's = to the potential energy. I'm not sure why, though.

 

[Lucretius]

Hmm I musta looked at it incorrectly. I meant the one with the graph and they wanted the two pieces of information to be put in. The optics one.

 

[Pseudo Statistic]

Oh, then you meant question 4.
For part a) you could basically use snell's law... n1 sin t1 = n2 sin t2.. and since n1 = 1 (air), you're left with:
sint1 = n2 sin t2 or n2 = sin t1 / sin t2
That's what you have to graph to get a linear relationship and thus, from the slope, calculate the index of refraction you need.
For part c, I'm not sure, but I'd guess "The air-oil interface only". (Not sure why though)
For part e there's a formula... 2t = something...

 

[jbusc]

e... I would integrate the coulomb force from infinity to the point, but I'm not sure if that's acceptable on physics B. You could say, instead, that it's = to the potential energy. I'm not sure why, though.

By the work-energy theorem, the work done on a particle is the change in the energy of the particle (potential energy, in this case) The potential energy of a particle at infinity is zero (because it's infinitely far away from the charges) So bringing a particle in from infinity, the potential energy is equal to the work done.

In AP physics, this is assumed to be true; you can show this using a little calculus 3, stating that since electric fields are conservative, the fundamental theorem of line integrals states the line integral of the field over the smooth curve from infinity to the final point (which is the definition of work) is just the difference between the potential function on the field at the endpoints.