su09Final

# su09Final - Physics 54 Summer 2009 Final Exam Solutions In...

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Physics 54 Summer 2009 1 Final Exam Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols given, and standard constants. If numbers are required, use g = 10 , k = 1/ 4 !" 0 = 9 # 10 9 and μ 0 = 4 ! " 10 # 7 (all in SI units). Part A: Multiple choice questions. Check the best answer. 1. Concerning the electro static field, which of the following is NOT true? As one follows a field line, the potential increases. [Decreases] Field lines start on positive charges and end on negative charges. Field lines never form closed curves. At a point on a conductor surface the field component perpendicular to the surface is proportional to the charge per unit area at that point. 2. A series LCR circuit is powered by a generator of rms voltage 100 V. The inductive reactance is 1000 Ω and the resistance is 100 Ω . The circuit is in resonance. The impedance is 1000 Ω . [ Z = R = 100 Ω ] The capacitive reactance is 100 Ω . [ X C = X L = 1000 Ω ] The rms voltage across the inductor is 1000 V. [ I = E / R = 1 A] The average power supplied by the generator is 10 W. [ P = I 2 R = 100 W] 3. Two rectangular loop circuits rest side by side as shown. In the left circuit the resistance of R is increased . The magnetic field created by the current in the left loop is into the page inside the right loop. [Out] The induced current in the right loop is clockwise. There is a net magnetic force on the right loop toward the left. [Magnetic moment of loop is parallel to B ] None of the above is true. + R

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Physics 54 Summer 2009 2 4. In the situation shown a grounded hollow conducting sphere has a positive charge + q at its center, and there is another positive charge + Q outside. The net charge on the outer surface of the sphere is zero. [It is negative] The charge + Q experiences a force to the left. [Attracted by the negative charge] The charge + q experiences a force to the left. [The interior is shielded, so there is no force on + q ] None of the above is true. 5. A copper plate is resting on a frictionless table, and a bar magnet a small distance above it is moving to the right as shown (in views from above). In case A the magnet is moving into the space directly above the plate; in case B it is leaving that space. The plate accelerates to the right in both cases. The plate accelerates to the left in both cases. The plate accelerates to the right in case A and to the left in case B. The plate accelerates to the left in case A and to the right in case B. [The force on the plate opposes the relative motion] 6. A person cannot focus clearly on objects farther away than 4 m or closer than 1 m. To correct these defects and allow focusing on objects between 0.25 m and infinity, bifocal glasses should have sections with focal lengths (in m): +4 and –3. –4 and +3.
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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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su09Final - Physics 54 Summer 2009 Final Exam Solutions In...

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