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Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for AP students and parents). 4 AP® PHYSICS C ELECTRICITY & MAGNETISM
2005 SCORING GUIDELINES
Question 2
15 points total
(a) Distribution
of points 3 points
The current through the inductor is zero immediately after the switch is closed ( I L = 0 ) .
Using Ohm’s law
V = IR
For the correct substitution of the emf e for the voltage V
For the correct substitution of the total resistance Rtot 1 point
1 point Rtot = R1 + R2 e = Iinit ( R1 + R2 )
For the correct answer
I init = e ( R1 + R2 )
(b) 1 point 3 points
For the correct application of the loop theorem to an appropriate loop of the circuit
For example, using the righthand loop containing L and R2
VR2 + VL = 0 1 point VR2 = R2 I init
VL =  L dI
dt dI
dt
This equation could also be obtained directly by recognizing that L and R2 are in parallel
and have the same voltage across them.
For the correct substitution of the current obtained in part (a)
dI
e
= R2
L
dt
R1 + R2
For the correct answer
R2 e
dI
=
dt
( R1 + R2 ) L
R2 I init = L 1 point 1 point Copyright © 2005 by College Entrance Examination Board. All righ...
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 Spring '08
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 Physics, Magnetism, AP, Magnetic Field, College Entrance Examination Board, college entrance examination, Entrance Examination Board

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