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 150. The exam period was 90 minutes; the mean score was 99.3 the median was 99. 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}.

(a) (b) (c) (d) (e)

(a) 3/4 kQ to the right (b) 128/9 kQ to the left (c) 160/9 kQ to the left (d) 160/9 kQ to the right (e) 128/9 kQ to the right

(a) kq^{2} / r (b) -kq^{2} / 6r (c) kq^{2} / 4r^{2} (d) -kq^{2} / 4r^{2} (e) kq^{2} / r^{2}

Consider the three positive charges in the configuration shown.

How much electrostatic potential energy does this system have?

(a) U = 23.0 kQ^{2} / d (b) U = 21.5 kQ^{2} / d (c) U = 0 (d) U = 14.5 kQ^{2} / d^{2} (e) U = -25.0 kQ^{2} / d

(a) 0.56d to the right of the 5Q charge (b) 0.56d to the left of the 5Q charge (c) d/2 to the right of the 5Q charge

Two small spheres with equal unknown mass are suspended by light-weight strings of length 12 cm. When a charge of +3 nC is placed on each sphere, each string makes an angle of 20° with the vertical in equilibrium.

What is the mass of each ball?

(a) 1.21 × 10^{-6} kg (b) 3.37 × 10^{-6} kg (c) 1.07 × 10^{-5} kg (d) 1.35 × 10^{-5} kg (e) 2.23 × 10^{-5} kg

(a) increase. (b) decrease. (c) remain the same.

Four capacitors are connected as shown below. A 15 V battery is centered in the circuit. Assume that all of the capacitors are fully charged and that no current is flowing.

What is the charge on one of the plates of the 4 μF capacitor?

(a) Q_{4} = 15 μC (b) Q_{4} = 30 μC (c) Q_{4} = 60 μC

(a) U_{tot} = 0.05 × 10^{-3} J (b) U_{tot} = 1.46 × 10^{-3} J (c) U_{tot} = 0.75 × 10^{-4} J (d) U_{tot} = 1.1 × 10^{-4} J (e) U_{tot} = 3.1 × 10^{-4} J

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 volts. Note the signs (+/-).

What is the sign (+/-) of the charge q_{2}?

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

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

(a) W = -4 J (b) W = -3 J (c) W = 0 J (d) W = +3 J (e) W = +4 J

Three capacitors are connected to a battery as shown in the diagram. The potential difference provided by the battery is 24 volts, while C_{1} = 8 μF, C_{2} = 6 μF and C_{3} = 4 μF.

What is Q_{1}, the charge on the capacitor C_{1}?

(a) Q_{1} = 6.0 × 10^{-5} C (b) Q_{1} = 8.4 × 10^{-5} C (c) Q_{1} = 10.8 × 10^{-5} C (d) Q_{1} = 14.4 × 10^{-5} C (e) Q_{1} = 19.2 × 10^{-5} C

(a) V_{3} = 4.8 V (b) V_{3} = 6.0 V (c) V_{3} = 9.6 V (d) V_{3} = 12.0 V (e) V_{3} = 14.4 V

Compare I_{2} (the current through R_{2}) with I_{3} (the current through R_{3}).

(a) I_{2} > I_{3} (b) I_{2} = I_{3} (c) I_{2} < I_{3}

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

(a) P = 1.95 W (b) P = 5.32 W (c) P = 11.9 W (d) P = 25.8 W (e) P = 30.8 W

(a) I_{2} = 0.232 A (b) I_{2} = 0.387 A (c) I_{2} = 0.459 A (d) I_{2} = 0.521 A (e) I_{2} = 0.692 A

Five resistors and three batteries are connected, as shown. Define the currents I_{1} through I_{4} with the directions given by the arrows.

Which one of these equations is valid?

(a) I_{1} + I_{2} + I_{3} - I_{4} = 0 (b) I_{1} + I_{2} + I_{3} + I_{4} = 0 (c) I_{1} - I_{2} - I_{3} - I_{4} = 0

(a) V_{A} - I_{1}R_{1} + I_{4}R_{4} = 0 (b) V_{C} + I_{2}R_{2} - V_{B} + I_{2}R_{5} - I_{3}R_{3} = 0 (c) V_{C} - I_{4}R_{4} + I_{3}R_{3} = 0

In the circuit shown, a switch can connect the top plate of the capacitor to either point A or point B. Assume that the switch was originally left at B for a very long time so that the capacitor is initially uncharged. Then at time t = 0, the switch is flipped over to connect to point A.

What is the current through the battery immediately after the switch is moved to position A?

(a) I(0+) = 0 (b) I(0+) = V_{b} / 40 (c) I(0+) = V_{b} / 20 (d) I(0+) = V_{b} / 10 (e) I(0+) = V_{b} / 5

(a) I = 0 (b) I = V_{b} / 40 (c) I = V_{b} / 20 (d) I = V_{b} / 10 (e) I = V_{b} / 5

(a) t_{A} < t_{B} (b) t_{A} = t_{B} (c) t_{A} > t_{B}

A doped semiconductor has a resistivity of ρ = 10^{-3} Wm. If a 1 micrometer thick slab of this material is to be cut into a resistor equaling 100 W, what dimensions should be chosen? (Note: the figure shown is not necessarily to scale.)

(a) w = 10 μm and L = 1 μm (b) w = 1 μm and L = 1 μm (c) w = 1 μm and L = 100 μm (d) w = 0.1 μm and L = 100 μm (e) w = 100 μm and L = 1 μm

A circuit consisting of resistors and a battery is shown. The battery voltage is V = 12 volts. The resistances shown in the diagram are all in ohms.

The magnitude of the current I through the leftmost 4 ohm resistor is:

(a) 2.0 A (b) 3.0 A (c) 3.4 A (d) 6.0 A (e) 9.0 A

(a) 2.0 ohms (b) 4.0 ohms (c) 6.7 ohms (d) 8.0 ohms (e) 16.0 ohms

(a) 1 A (b) 2 A (c) 3 A (d) 4 A (e) 12 A

(a) 12 watts (b) 24 watts (c) 36 watts (d) 48 watts (e) 144 watts