Exam II solutions

Exam II solutions - PH 132 Exam 2 Sprirg 2005 Student Name...

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Unformatted text preview: PH 132 Exam 2 Sprirg 2005 Student Name SOL (fr {0 M 5 Student Number Labeecitation Section Number (11,...,35) Instructions: 1. 2. 3. Fill out all information above. Write your name on each page. Clearly indicate your final answers for all multiple-choice questions in the Space provided. Present neat and orderly solutions to each problem. Clearly indicate your method of solution by including equations used for each part. Final answers should be circled or boxed. Be sure to include appropriate units with all answers. Assume the reference potential at infinity is zero unless specified otherwise. Multiple Choice Problem 1 Problem 2 Total Multiple Choice (2 pts. each) “D N n at In; .1: | to (a LII-J | l 10V 20V 30V 40V 50V 1) What is the direction of the electric field associated with the surfaces? A) Rightward; B) Leftward; C) Upward; D) Downward; E) Into the page; F) Out of the page. Answer B 2) Rank the paths according to the work you do in moving each charge, greatest first. (Note that sometimes the work is positive and sometimes it is negative.) want. 31’ You‘- 3) 1,3,2; m 20 5 C) 2,1,3; w, = (-eysov—iov = W0 t: ED; N3, = (e) (‘IDV-‘z-W) = 3-D e F) 3:2:1: N5: (“WOW An”) = wAgswer__F.__ . 3) What is the net electric potentiai at the origin due to the three charges positioned as shown? Each charge resides at a distance a away from the origin. A) 0; B) — 39-, a C) 4:3; 0 D) ii; a E) 391. Answer b a 4) How much electrostatic potential energy is stored by the assembled charge distribution in the previous roblem'? B) _k29'. " stews-66' a ’ Samar race). 2 W :0 C) 49—, I __ «i q“; :32 " "22 (kg—:1 \ D) kb’ : Z - 3 a2 3 a; (L751 4» Lg} E) 162i Answer B w'f'of = wl 4'sz +N5 a”; * 7;: 5) The following figure shows three pairs of parallel plates with a separation distance of either d or (W, and the electric potential of each plate. The electric field between the plates is uniform and perpendicular to the plates. Rank the pairs according to the magnitude of the electric field between the plates, greatest first: :r'usl' r256 : -30V +30V —1 -3V Ex' _.' I FDR. EAOH, K O 2:: N a) I 5' A) a, b, c; V -V; = - '55.; “0° Part} B) a, c, b; 5 p C) b,a,c; Q .39V .39V .-: - ,: va D) be Ca 3; -mV qoov E) 0,3,1); A E E= 221’ 9 F) c, b, a; é “VWV'” ("3"?) = '"E‘L "4' E: 13’." Answer 6) When the potential difference V across a parallel plate capacitor is doubled, the capacitance C and the charge q, respectivel : Z 2 VC A) decreases, decreases; B) decreases, increases; a I, “germT Cugmfwagfomafl-‘A C) decreases, remains the same; a . . o D) Increases, increases; ‘5 ,3 I}: V 4‘ 731:5“ a 1‘ _ E) increases, decreases; F) remains the same, increases. Answer E 7) A slab of copper is inserted into a parallel plate capacitor of plate area A and plate separation d, as shown. The slab has the same area A but thickness df4. After the slab is introduced, the capacitance: “M AT As :1," GUKQWfi-S l“ C = . C. = I 5 7V; 2. 5. q A) increases by a factor ofA’; ‘1’; B) increases by a factor of 153 33/5 C) decreases by a factor of M; 34! A :g D) decreases by a factor of 5/6 Answer 8) A Tungsten resistor is connected to a battery that provides a constant potential difference. A hot plate is used to heat the resistor. Note that the temperature coefficient of resistivity for Tungsten is positive. What will happen to the conductivity and current density, respectively, as a result of this proc A) decreases, decreases; . B) decreases, increases; C) increases, decreases; D) increases, increases. - Answer A 9) The following figure shows a portion of a circuit with multiple intersecting wires. What are the magnitude and direction of the current in the lowest wire? A) 2 A upward; B) 2 A downward; C) 4 A upward; D) 4 A downward. Answer_£_ 10) In the following figure, with R1 = R2 = R3, the power dissipated by R3 is times the power dissipated by R}. A) 1K4; B) 1f2; C) 2; D) 4. Answer b BONUS: Assume that one end of a 4.0 ,u F capacitor is connected to point a and the other end 4 VOLTAGE: £59105 LOOP; \\-/’_Vs = 0 L99? 2. ‘YI-PVB "Vz'Vg = 0 L092 3 \/l "V; =0 Problem 1 Consider the following circuit with five fully charged parallel-plate capacitors. Assume that each capacitor has no dielectric material between its plates. a) Find the equivalent capacitance of this circuit. (2 pts.) b) Find the charge on each capacitor and the potential déflerence across each capacitor. (12 pts.) c) Find the magnitude of the potential difl‘erence between points a and b. (2 pts.) 6 (1) Which capacitor stores the most enery? How much does it store? A piece of plastic with a dielectric constant of 1.5 is inserted between the plates of this capacitor. Find the energy j stored by this capacitor after it recharges. (4 pts.) ‘ is connected to point b. What is the new equivalent capacitance of the circuit? (3 pts.) Problem 2 Consider the following circuit: Note that the directions for the currents have been chosen for you. R2 a) Find 1., 12, and I; and indicate whether or not the assumed current directions are correct? ( [2 pts.) b) Find the power dissipated in each resistor. (4 pts.) c) Find the power delivered to or by each battery. You must indicate “delivered to” or “delivered by” for each. Which battery (if any) is being charged? (3 pts.) LOOP R955 0) 3+ 2.1: ® ’2- 123m: _ .. '- — ‘= C3 "hP 1. -"-7 ———-! “LI :- 3 El IJRI *5: 1:12 +4323 £3 ' 3 Loo? “‘5 (A Lap? RULE (3-3 .. z—r g3_za]a3 -3332“, = c: wris- RUG, Nab Inn: Q: 31-21; +3; 3 2-1]; 12"53 '3Il to (.99? real-'5 (3" £3— 91—3 =° 59w??- ‘. ...
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Exam II solutions - PH 132 Exam 2 Sprirg 2005 Student Name...

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