PHYS 212 – MT2 Summer 2012 Sample 3 Question 1 Two charges lie on the x-axis. A representation of the equipotentials of the electric potential of these two charges is shown below. The "streaks" in this representation are parallel to the equipotential curves Which one of the following statements about the sign and magnitude of the charges is true? Compared to the right charge, the left charge… A. B. C. D. E. has the opposite sign and is smaller in magnitude. has the opposite sign and is larger in magnitude. has the same sign and is smaller in magnitude. has the same sign and is larger in magnitude. has the same sign and the same magnitude. Page 1 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 Question 2 In the figure, what should be the position of the switches for the potential across R to be zero? A. B. C. D. E. S1 open, S2 closed. Both open. S2 open, S1 closed. Both closed. More than one answer above is right. Question 3 In the diagram R1 > R2 > R3. Rank the three resistors according to the voltage across them, least to greatest. A. All are the same B. V3 < V1 < V2 C. V3 < V2 < V1 D. V1 < V3 < V2 E. V1 < V2 < V3 Page 2 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 Question 4 Consider the circuit drawn below. Given the way the currents are labeled, which of the following equations is correct? Start from point a and proceed clockwise around the outer loop A.  I1R1  I 2 R2   2  1  0 B. I1R1  I 2 R2   2  1  0 C.  I1R1  I 2 R2   2  1  0 D.  I1R1  I 2 R2   2  1  0 E.  I1R1  I 2 R2   2  1  0 Question 5 Positive charge is distributed uniformly throughout a solid non-conducting sphere. The highest electric potential occurs: A. B. C. D. E. at the center at the surface halfway between the center and surface just outside the surface far from the sphere Page 3 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 The next three questions refer to the figure at right, which shows some equipotential lines in a region of space. Question 6 A proton is released from rest at point A. In which direction will it initially start moving? A. Up B. Down C. Right D. The proton will drift along the 0 V contour line, in either direction E. The proton will remain at rest Question 7 At which of the three labeled points (A, B, C) is the electric field the strongest? A. At the point A B. At the point B C. At the point C D. It is equally strong at points A and B (but is stronger at both of those than at point C) E. It is equally strong at points B and C (but is stronger at both of those than at point A) Question 8 Now consider moving a proton from point B to point C with constant velocity. How much external work would this take (i.e. how much work would you need to do)? A. -3 eV B. +3 eV C. -6 eV D. +6 eV E. -1.6 ⋅10-19 eV F. +1.6 ⋅10-19 eV Page 4 of 10 PHYS 212 – MT2 Summer 2012 Question 9 A parallel plate capacitor has a charge-potential differential relationship as plotted in the solid line at right. It is connected to a battery and charged so that its state is indicated by the big blue dot. With the battery still connected, you do positive work on the plates of the capacitor in order to modify its charge-potential difference relationship to one of the two dashed lines. At which, if any, of the 4 labeled states does the capacitor end up? A. B. C. D. E. Sample 3 q B A D C V A B C D None of the above Question 10 Two points, A and B, are in a uniform electric field which points up the page, as shown, with magnitude 15 N/C. Point A is located at the origin (x,y) = (0 m, 0 m) Point B is located at (x,y) = (3 m, 4 m) The zero of voltage has been chosen to lie at point A. What is the voltage at point B? A. B. C. D. E. F. G. H. I. J. +15 V -15 V +45 V -45 V +60 V -60 V +75 V -75 V Impossible to determine given the above information None of the above Page 5 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 The following two questions use the same set-up A positive charge q sits on the top vertex of an equilateral triangle, with two unknown charges q2 and q3 on the other two vertices. The point P is at the center of the triangle and is a distance a from each of the charges (see sketch) and a distance a/2 up from the base of the triangle. If we define the electric potential at infinity to be zero, we find that the electric potential at point P is also zero. Moreover, we find that the electric field at point P points purely along the y-axis. Question 11 What is the charge q2? A. q B. –q C. 2q D. -2q E. q/2 F. –q/2 G. Cannot determine from the given information H. None of the above Question 12 How much work would you need to do to bring a positive charge Q from infinity to the origin (midway between the charges q2 and q3)? A. 2kqQ 3a B.  2kqQ 3a 3kqQ C. a 3kqQ D.  a E. 0 F. None of the above Page 6 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 The next four questions all depend on the following setup. A C V = 10 V 12 10 (0.1 s, 9.0 V) 8 11 6 I1 (mA) Voltage across elementB (volts) The circuit at right consists of a 10 V battery, a switch S, and three other circuit components (either resistors or capacitors), hidden in boxes labeled A, B & C. You are given the circuit, in which the switch has been open for a very long time, and asked to determine what is in the boxes. You close the switch and record the voltage across element B and the current I1 through element C. You also tried to record the current I2 through A & B, but unfortunately only got its value the instant the switch was closed, which was I2(t=0+) = 10 mA. VB and I1 are plotted below: B (0.7 s, 5.0 V) 4 (1.0 s, 10 mA) 10 (10.0 s, 10 mA) (1.1 s, 3.3 V) 9 2 8 0 0 2 4 6 Time (seconds) 8 10 0 2 4 6 8 10 Time (seconds) Question 13 What circuit element is in box C, and what is its numerical value (i.e. resistance if a resistor, capacitance if a capacitor)? A. B. C. D. E. F. G. 1 10  1 k 1 mF 10 mF 100 mF None of the above Page 7 of 10 PHYS 212 – MT2 B C V = 10 V Voltage across elementB (volts) A Summer 2012 Sample 3 10 (0.1 s, 9.0 V) 8 6 (0.7 s, 5.0 V) 4 (1.1 s, 3.3 V) 2 0 0 2 4 6 8 10 Time (seconds) Question 14 What circuit element is in box B, and what is its numerical value (i.e. resistance if a resistor, capacitance if a capacitor)? A. B. C. D. E. F. G. 1 10  1 k 1 mF 10 mF 100 mF None of the above Question 15 What is the approximate time constant of the voltage decay across element B? A. 0.1 s B. 0.6 s C. 0.7 s D. 1.0 s E. 1.1 s F. 2.0 s Question 16 What circuit element is in box A, and what is its numerical value (i.e. resistance if a resistor, capacitance if a capacitor)? A. B. C. D. E. F. G. 1 10  1 k 1 mF 10 mF 100 mF None of the above Page 8 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 Question 17 The circuit at left consists of three identical resistors each with resistance R, two identical batteries with emfs , and a capacitor with capacitance C. The capacitor is initially uncharged at t = 0. After a very long time, what is the charge Q (as labeled in the picture) on the capacitor? A. B. C. D. E. F. G. Q  23 C Q  C Q  12 C Q0 Q   12 C Q  C Q   23 C Question 18 A parallel plate capacitor is charged using a battery and the battery is then removed. The plates of the capacitor are now brought closer together. Which of the following statements is FALSE? A. The electric field inside the capacitor remains the same. B. The potential difference between the plates of the capacitor decreases. C. The capacitance of the capacitor increases. D. The charge on the capacitor remains the same. E. The energy stored in the capacitor increases. Page 9 of 10 PHYS 212 – MT2 Summer 2012 Sample 3 Question 19 A 12 V car battery connected to 10  resistor supplies 1 A of current. What is the maximum current that the battery can supply? A. B. C. D. E. F. 1 A 1.2 A 2 A Theoretically it could supply any amount of current There isn’t enough information provided to determine the maximum (but there is one) None of the above Question 20 Two uncharged conductors, A and B, are of different sizes. They are charged as follows: 1. A is charged from an electrostatic generator to charge q. 2. A is briefly touched to B. 3. Steps 1 and 2 are repeated until the charge on B reaches a maximum value. After the first touch the electrostatic energy associated with B is four times that of A (when they are well isolated from each other). After the process is complete (after B has been charged as completely as possible) how much charge is on B? A. B. C. D. E. F. q/4 q/2 q 2q 4q None of the above Page 10 of 10