***Official Physics B thread 2012-2013***

<p>its (Thot-Tcold)/Thot</p>

<p>solve for b with permittivity of free space/2pi * (I/r)</p>

<p>I agree with that, but if you’re looking for the I for wire Y, and you don’t know I, how can you solve for B?!</p>

<p>yeah so was the other temperature 90k or 1000k?</p>

<p>It was 1000K</p>

<p>i used current given for wire x…</p>

<p>OHHHHHH that makes sense now.</p>

<p>Oh well, got that wrong.</p>

<p>But what direction did the current go in for wire Y?</p>

<p>damn. i put 1000k then changed it to 90 DX</p>

<p>I said y went left</p>

<p>i got current wrong but maybe i got the others right,
potential equal on all ends, current going left because the wires repel (made some bs), if it gets moved to top everything stays the same. If it gets moved up the wire will move down due to repulsion.
please tell me i’m atleast partially right somewhere.</p>

<p>why is there a current in wire y? the magnetic flux was not changing so there shouldnt be a current</p>

<p>What did you guys get for the current?</p>

<p>Free response:</p>

<h1>1 was the fluid with the sailboat</h1>

<p>a) B/T up, Fg down
b) Buoyancy 61.25N
c) tension 428.75N
d) I put D’ > D and explained saying no longer a tension of the rope (not sure about this one)</p>

<h1>2 Object goes into spring at 4m/s</h1>

<p>a) Work was negative
b) magnitude of work? c) spring constant d) frequency
kinetic energy graph I did concave down with 0 as max
acceleration graph I did concave up with 0 as min</p>

<h1>3 finding index of refraction by graphing</h1>

<p>I set up sin(theta i) on y-axis and sin(theta r) on x-axis
b) 1.4 for the index of refraction (slope) - would 1.5 work?
don’t remember other part to this question</p>

<h1>4 Projectile with the ball leaving the cup (not sure if these are right)</h1>

<p>a) Speed out of cup I got 2.57m/s
b) Acceleration I got 3.67 m/s^2
c) Mass of ball .838kg</p>

<h1>5 Thermo question</h1>

<p>a) 1100J
b-d) not sure if right but I put volume goes down, pressure goes down, temperature goes up
e) Internal energy change 0J because said constant temperature?</p>

<h1>6 electricity question</h1>

<h1>7 energy levels</h1>

<p>a) was this 552nm or did I get this wrong?
ionization 12ev
don’t remember other parts</p>

<p>magnetism is my weak spot. Darn i guess ill get like 3 points then for this problem. i think you’re right moss. But what about the potential</p>

<p>for 5 i put that v goes down p and t go up</p>

<p>V goes down
P stays the same
T goes up</p>

<p>@eswara I put mostly the same things. I wasn’t really sure about any of them, although I do know that the electric potential was higher on the side that the force of the magnetic field was pointing when you used RHR (I don’t remember if it was right or left) because the force will push negative charges to one end, leaving positive charges on the other.</p>

<p>no clue on 5…</p>

<p>What did you get for the acceleration of the block?</p>

<p>v definately goes down, t definately goes up and pv/t is constant so p has to go up.</p>