su11FinalS

# su11FinalS - Physics 54! Summer 2011 Final Exam Solutions...

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Final Exam Solutions If numbers are required, use g = 10, k = (4 πε 0 ) 1 = 9 × 10 9 , μ 0 / 4 π = 10 7 and c = 3 × 10 8 (all in SI units). Part A: Multiple choice questions, 4 points each. Check the best answer. 1. The left sides of the four Maxwell equations are (1) E d A (2) E d r (3) B d A (4) B d r and the right sides are (a) 0 (b) Q enc / ε 0 (c) 0 I linked + 0 E t d A (d) B t d A The correct matches of the two sides are: (1) = (a), (2) = (b), (3) = (c), (4) = (d). (1) = (b), (2) = (a), (3) = (c), (4) = (d). (1) = (d), (2) = (a), (3) = (c), (4) = (b). (1) = (b), (2) =(d), (3) = (a), (4) = (c). 2. Two point charges are on the x -axis. Taking V to vanish at inFnite distance, there is no point on the axis between the charges where the total potential is zero. The total potential is zero at some point(s) on the Fnite x -axis. The total E-Feld vanishes at a point on the axis between the charges. The potential energy stored in the system is negative. None of the above is true. [Charges have the same sign.] Physics 54 Summer 2011 1

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3. Shown is a thundercloud, a tall building, and a tree. Lightning from the cloud is more likely to strike: The building because it is closer to the cloud and therefore the potential difference between them is greater. [Same.] The building because it is closer to the cloud, and therefore the E-Feld is greater between them. Either is equally likely because they are at the same potential. Either is equally likely because the E-Feld between them and the cloud is the same. 4. A beam of electrons and protons of the same speed traveling parallel to each other enter a region of uniform magnetic Feld perpendicular to their initial velocity. What occurs? They move in identical circular arcs. They move along circular arcs of the same radius, but in opposite directions (i.e., one clockwise, the other counter-clockwise). They move in circular arcs, but in opposite directions, and the radius of the electrons’ arc is larger. They move in circular arcs, but in opposite directions, and the radius of the electrons’ arc is smaller. [ r = mv / qB .] 5. A ray of unpolarized light is incident on a block of glass at an angle such that the re±ected ray is completely linearly polarized. The arrow that best represents the refracted ray is 1. 2. [ θ 1 + 2 = π /2 .] 3. None of the above. 1 2 3 Physics 54 Summer 2011 2
6. A fat horizontal glass plate ( n = 1.6 ) has a Flm o± water ( n = 1.33 ) on it, and white light refected by this system is viewed ±rom above. As the water Flm becomes very thin just be±ore it evaporates: The refected intensity is unusually high ±or all wavelengths. [ δ 0 .] The refected light is bluish violet in color. The refected light is reddish orange in color.

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## This note was uploaded on 10/19/2011 for the course PHYSICS 54L taught by Professor Thomas during the Summer '09 term at Duke.

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su11FinalS - Physics 54! Summer 2011 Final Exam Solutions...

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