Final_2005Fall_Solutions

Final_2005Fall_Solutions - MIT Department Of Physics Final...

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MIT Department Of Physics Final Solutions Fall 2005 p. 1 of 20 Problem 1: Ten Short Questions. Circle your choice for the correct answer Each problem is worth 4 points for the correct answer or 1 point for admitting that you don’t know how to do it. Unanswered or incorrectly answered problems will earn a 0. Question A (4 points out of 40 points): In lab 1 you fixed the potential difference between two plates and measured equipotential lines from which you determined electric field lines and approximate charge distributions. You are given the two conducting plates at left, with the top plate held at +5 V relative to the bottom plate. What can you say about the relative magnitude of the charge densities near the four locations indicated? 1. |Q(A)| ~ |Q(C)| > |Q(B)| ~ |Q(D)| 2. |Q(A)| > |Q(B)| ~ |Q(C)| > |Q(D)| 3. |Q(A)| ~ |Q(B)| > |Q(C)| ~ |Q(D)| 4. |Q(D)| ~ |Q(C)| > |Q(B)| ~ |Q(A)| 5. |Q(B)| ~ |Q(D)| > |Q(A)| ~ |Q(C)| 6. |Q(A)| > |Q(D)| ~ |Q(C)| > |Q(B)| 7. |Q(C)| > |Q(A)| ~ |Q(B)| > |Q(D)| 8. I don’t know (this answer is worth 1 point) Question B (4 points out of 40 points): In the second lab you worked with a Faraday pail, two nested conducting cylinders as pictured at left. You held the outer cylinder at ground (i.e. at the same potential as infinity) and measured the potential of the inner cylinder relative to the outer cylinder. For one of the measurements you started from a condition where both cylinders were uncharged, introduced a positive charge producer into the central region, briefly connected the inner at outer cylinders with a conductor (your finger) and, after removing the connection, removed the positive charge producer. The positive charge producer never touched either of the cylinders during this measurement. Which of the following statements about the surface charges at the end of this measurement is true? I1 I2 O1 O2 1. Q(I1) = 0; Q(O1) = 0; Q(I2) = 0; Q(O2) = 0 2. Q(I1) = 0; Q(O1) < 0; Q(I2) > 0; Q(O2) = 0 3. Q(I1) = 0; Q(O1) < 0; Q(I2) > 0; Q(O2) < 0 4. Q(I1) = 0; Q(O1) > 0; Q(I2) < 0; Q(O2) = 0 5. Q(I1) = 0; Q(O1) > 0; Q(I2) < 0; Q(O2) > 0 6. Q(I1) < 0; Q(O1) > 0; Q(I2) < 0; Q(O2) > 0 7. I don’t know (this answer is worth 1 point)
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MIT Department Of Physics Final Solutions Fall 2005 p. 2 of 20 Question C (4 points out of 40 points): In the third lab you constructed the circuit at left in order to study the effects of capacitors in circuits. You measured the current through and voltage across the resistor R using the ammeter and voltmeter as pictured at left. The battery would periodically switch on and off, allowing you to measure their “initial” values (right after the battery switched on) and their “final” values (a long time after the battery was switched on). After measuring the behavior in this circuit you had the opportunity to add a second resistor in parallel with the capacitor C . After adding th e second resistor which of the following statements is true? . Neither the initial current nor the final voltage changed the same 1 2. The initial current was smaller but the final voltage was 3. The initial current was larger but the final voltage was the same 4. The initial current was the same but the final voltage was smaller 5. The initial current was the same but the final voltage was larger 6.
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Final_2005Fall_Solutions - MIT Department Of Physics Final...

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