True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 123. The exam period was 90 minutes; the mean score was 73.3 the median was 73. Click here to see page1 page2 page3 of the formula sheet that came with the exam.

Some helpful information: • A reminder about prefixes: p (pico) = 10^{-12}; n (nano) = 10^{-9}; μ (micro) = 10^{-6}; m (milli) = 10^{-3}; k (kilo) = 10^{+3}; M or Meg (mega) = 10^{+6}; G or Gig (giga) = 10^{+9}.

Two charges are located on the x axis as shown in the figure.

d = 15 cm q_{1 }= -2 μC q_{2 }= +3 μC

What is the electrostatic energy U of the system comprised of charges q_{1 }and q_{2 }?

(a) U = -2.4 J (b) U = -0.36 J (c) U = 0 (d) U = +0.36 J (e) U = +2.4 J

(a) q_{3} = -24.75 μC (b) q_{3} = -11.2 μC (c) q_{3} = -2 μC (d) q_{3} = 11.2 μC (e) q_{3} = 24.75 μC

(a) q_{4} = -11.2 μC (b) q_{4} = -2 μC (c) q_{4} = -1.5 μC (d) q_{4} = 1.5 μC (e) q_{4} = 11.2 μC

Given is a map of equal-potential lines (see figure below). The potential is created by three charges in a plane (q_{1}, q_{2}, q_{3}). Potential values are given in V. Note the signs (+/-).

Based on the map, what is the sign (+/-) of the charge q_{3 }?

(a) - (b) 0 (c) +

(a) left (b) right (c) up (d) down (e) cannot be determined

(a) W = -5 J (b) W = 0 J (c) W = 5 J

Given are 4 charges on a square of side a = 25 cm (see figure above). q = 1 μC.

What is the x component of electric field at the center of the square (E_{x})?

(a) E_{x} = -611,000 N/C (b) E_{x} = -204,000 N/C (c) E_{x} = 0 N/C (d) E_{x} = 204,000 N/C (e) E_{x} = 611,000 N/C

(a) E_{y} = -611,000 N/C (b) E_{y} = -204,000 N/C (c) E_{y} = 0 N/C (d) E_{y} = 204,000 N/C (e) E_{y} = 611,000 N/C

(a) V = -288,000 V (b) V = -51,000 V (c) V = 0 V (d) V = 51,000 V (e) V = 288,000 V

(a) W = -0.22 J (b) W = -0.11 J (c) W = 0 J (d) W = 0.11 J (e) W = 0.22 J

A small sphere of mass m = 0.4 grams is positioned in the middle between two capacitor plates (see figure above). The sphere is charged and at rest. The plates are horizontal, at a space d = 8 cm apart. The capacitor is connected to an electromotive force of 15V.

What is the magnitude of the electric field E between the plates?

(a) E = 1.2 V/m (b) E = 1.9 V/m (c) E = 187.5 V/m

(a) q = -20.9 mC (b) q = -20.9 μC (c) q = 0 C (d) q = 20.9 μC (e) q = 20.9 mC

(a) down (b) up (c) will not move

Two identical capacitors are each built from square plates, each of side a. The distance between the capacitor plates is d. Between them is a medium with dielectric constant κ.

Plate 1 is connected to the positive terminal of a battery of Voltage V, while plate 4 is connected to the negative terminal (see figure).

What is the capacitance C of the system?

(a) C = κ ε_{0}a^{2} / 2d (b) C = κ ε_{0}a^{2} / d (c) C = 2 κ ε_{0}a^{2} / d

(a) U = κ ε_{0} a^{2}V^{2}/ 4d (b) U = κ ε_{0} a^{2}V^{2}/ 2d (c) U = κ ε_{0} a^{2}V^{2}/ d

(a) q_{2} = - V κ ε_{0} a^{2} / 2d (b) q_{2} = 0 (c) q_{2} = V κ_{} ε_{0} a^{2} / 2d

Compare I_{3}, the current through resistor 3, with I_{4}, the current through resistor 4.

(a) I_{3} > I_{4} (b) I_{3} = I_{4} (c) I_{3} < I_{4}

(a) V_{1} > V_{5} (b) V_{1} = V_{5} (c) V_{1} < V_{5}

(a) P = 23.4 W (b) P = 37.1 W (c) P = 48.8 W (d) P = 62.7 W (e) P = 132 W

(a) I_{2} = 0.27 A (b) I_{2} = 0.45 A (c) I_{2} = 0.94 A (d) I_{2} = 1.32 A (e) I_{2} = 3.17 A

Capacitors C_{1} and C_{3} relative to each other are

(a) in parallel. (b) in series. (c) neither in series nor in parallel.

(a) |V_{2}| > |V_{4}| (b) |V_{2}| = |V_{4}| (c) |V_{2}| < |V_{4}|

(a) U = 93 μJ (b) U = 124 μJ (c) U = 215 μJ (d) U = 328 μJ (e) U = 583 μJ

(a) Q_{1} = 29.2 μC (b) Q_{1} = 41.4 μC (c) Q_{1} = 52.4 μC (d) Q_{1} = 61.0 μC (e) Q_{1} = 73.8 μC

In the circuit shown, the switch has been open for a long time so that the capacitor is uncharged.

What is the current through the battery immediately after the switch is closed?

(a) I(0+) = 2V/R (b) I(0+) = V/(2R) (c) I(0+) = V/R

(a) (b) (c)

(a) Q(∞) = CV/2 (b) Q(∞) = CV (c) Q(∞) = 2CV

(a) t = RC/2 (b) t = RC (c) t = 2RC