<p>I thought bulb was brighter</p>
<p>Bulb remains the same cause current was given as I=Imax-Kt where Imax and K are constants and t is time.</p>
<p>Emf is -L*dI/dt and dI/dt for this case is simply -K. Thus, induced emf is LK.</p>
<p>Since the emf is not changing, the brightness remains the same</p>
<p>Take a look at number 3 on the E&M free response for the year 2004. It’s almost identical to the one that we had this year. You have to split up the dA integral into dA=bdr, and then integrate. You integrate in this method where dr is changing radially outwards because the magnetic field changes in that direction as well. (not along the wire).</p>
<p>Also for the circuit one, when the switch was closed, I assumed that no current would pass through the capacitors. Is that really right? It makes more sense that the capacitors would take some initial current and then have a charge, but that sounded way to difficult so I didn’t even try it.</p>
<p>-LdI/dt would only make sense if the light bulb was an inductor. The brightness depends on the power. Since the current drops, the bulb gets dimmer. At least I would think…</p>
<p>Brightness does depend upon power. And P= V^2/R. R is constant, and V is constant, so Power is constant, and brightness is constant. How is V constant? E = -d(Magnetic Flux)/dt. That ends up being a constant.</p>
<p>I took mechanics this year as a junior and I’m taking E&M as a senior next year.</p>
<p>If I didn’t get a 5 on mechanics, I’m retaking it next year. I love how my school separates AP Physics classes like it does.</p>
<p>can we talk about the specific FR questions now? Really want someone to explain how to do 1 and 3 on the Physics C Mechanics.</p>
<p>We’re supposed to wait 48 hours/when CollegeBoard puts them up on APCentral.</p>
<p>i thought e and m was way harder than mechanics…</p>
<p>so the curves for mechanics was 47/90 for 5 last year and 50/90 for e & m. guesses on curve this year?</p>
<p>Well if we take it to the logical conclusion, where there I=0, is the bulb still bright? It doesn’t make any sense</p>
<p>I think we can talk about them now. It’s been just about 48 hours, if not more.</p>
<p>My Opinions:</p>
<p>Mech:
MC - More difficult than normal, but fairly easy.
1- Easy
2- Easy
3- A lot of integration, but easy for someone like me who likes calculus-based approaches</p>
<p>E&M
MC - Not too bad, I got tripped up on some questions though.
1- Not bad
2- I hate circuits so I’m biased on this one lol.
3- Not too bad either, I think I may have messed up a bit.</p>
<p>I heard someone ask how do you find work if given Force as a function of time. I didn’t take the test, but the integral of Power<em>dt = the work done. If you have the force as a function of time and the velocity as a function of time you can do P(t) = v(t)</em>F(t) and then integrate that.</p>
<p>I found the change in Kinetic and potential energies and set the work equal to that by conservation of energy.</p>
<p>so, now that we can talk abt it,
on #3 on mech, did we have to solve the integral for full credit? All it said was to derive the formula. It never said we had to get rid of integration signs or anything.</p>
<p>Oh crap, on mech #3 I only set the work equal to change in kinetic energy. Think I’ll at least get some partial credit for that?</p>
<p>I didn’t take C mechanics this year, planning to take it next year.
Hope someone can tell me more specificly about what was on the test in FR part?</p>
<p>College Board should have them up in a few hours. I still can’t remember anything very well.</p>
<p>Mechanics:
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>E&M:
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<p>does late testing have the same questions as the normal one? I know someone who is not taking this till next week. It seems kind of unfair</p>
<p>Obviously not.</p>
<p>Edit: Links to the FRQs at the bottom of page 8</p>