The Official AP Physics B Thread

Test Preparation AP Test Preparation
181

<p>just to ease people’s fears about the curve…</p>

<p><a href=“http://02b9104.netsolhost.com/hiviz_org/apb89/ap/ap_exams/2004_AP_Scoring.pdf[/url]”>http://02b9104.netsolhost.com/hiviz_org/apb89/ap/ap_exams/2004_AP_Scoring.pdf&lt;/a&gt;&lt;/p&gt;

<p>this is the OFFICIAL scoring worksheet from 2004.</p>

<p>if you read it, 115-180, or about 64%, is a 5</p>

<p>good luck tm</p>

182

<p><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;

183

<p>^^ that kinda cheers me up that abut 60% of the students scored 3 or higher on last year’s test.</p>

184

<p>A object is thrown straight up. When it’s going upwards, is the acceleration positive and when its coming downwards, is the acceleration negative? I am kinda confused abut that.
ty</p>

185

<p>acceleration, assuming no other forces act on it, is g, which is -9.8 m/s^2. It’s always negative.</p>

<p>Velocity is positive going up and negative going down.</p>

186

<p>ah, thank you.</p>

187

<p>Yeah there is no such thing as deceleration. Only velocity decides the direction. Acceleration is just the rate of change of velocity. It can be negative or positive.</p>

188

<p>Yeah there is no such thing as deceleration.</p>

<p>:o What!?!</p>

189

<p>I’m at a crossroads…I really don’t understand optics at all and, well, it’s the day before the test and my review book isn’t helping; should I just cut my losses and focus on the rest or is optics really that important?</p>

190

<p>optics is prolly like a couple of questions…just move on.</p>

191

<p>i’m confused about direction of induced current caused by magnetic flux (lenz’s law basically). can someone clarify it for me? much appreciation</p>

<p>oh, i’ve read through pr, done extra problems, and the test hopefully wont be bad.</p>

192

<p>

</p>

<p>This is difficult to explain in words, but I’ll give it my best shot.</p>

<p>Lenz’s law basically states that the induced current will be the opposite of what the flux is creating. Allow me to clarify through an example.</p>

<p>If you have a rectangular loop of wire, and it is moving with a certain velocity v out of a magnetic field directed into the page (depicted as x’s on the AP exam), Lenz’s law states that the induced current will be clockwise. Here’s why: as the wire moves out of the magnetic field in the -z direction, it is losing x’s; Lenz’s Law states that to counterbalance this loss, more x’s will be created. As such, the curled hand rule informs us that the current created by these x’s will run in the clockwise direction.</p>

<p>I hope this makes sense and is helpful. If you’re still confused, please do ask a specific question about what I’ve written.</p>

193

<p>how do you do the questions that, after providing you a chart, ask something like, "which of the following photon energies could NOT be found in the emission spectra of this atom after it has been excited to the n = whatever state? doesn’t it have to do with the difference in the energy levels or something?</p>

194

<p>Do you have a sample problem of the aforementioned nature?</p>

195

<p>A hypothetical atom has four energy states as shown below.</p>

<p>eV n
-1 4
-2 3
-4 2
-7 1</p>

<p>Which of the following photon energies could NOT be found in the emission spectra of this atom after it has been excited to the n=4 state?</p>

196

<p>Anyone else besides me thinking of bailing on this? Anyone know if it even is possible to bail this late? I’m averaging 28 correct / 9 wrong / 33 skipped on the multiple choice…</p>

197

<p>^^ The answer is 4eV because you can not change energy levels by 4eV to any of the emission boundaries.</p>

<p>For example, 1eV is possible from n=3 to n=4 (add 1 to -2 and you get -1)
2eV is possible from n=2 to n=3 (add 2 to -4 and you get 2)
3eV is possible from n=1 to n=2 (add 3 to -7 and you get 4)
5eV is possible from n=1 to n=3 (add 5 to -7 and you get -2)</p>

198

<p>um I still don’t get it :(</p>

199

<p>Here’s a simple trick. See those eV numbers next to the n levels? Like 7 next to n = 1? Just randomly subtract them from each other. </p>

<p>7 - 4 = 3
4 - 2 = 2
2 - 1 = 1
7 - 2 = 5</p>

<p>Whichever sum you can’t “get,” is the invalid number of energy released. In your case, no combination of subtraction can produce 4, so that’s the answer.</p>

200

<p>OHHHHHH OK…Gotcha!
Man, I feel dumb. TY An0maly! :smiley:
And Ty diligency92! :)</p>