Ex1_F08 - Physics 241 Fall 2008 Exam 1 October 1, 2008...

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Unformatted text preview: Physics 241 Fall 2008 Exam 1 October 1, 2008 Giving information to or receiving information from another person while taking this exam is cheating. To intentionally do anything that would cauSe the level of your knowledge of the material to be misrepresented is cheating. Anyone found to be cheating will receive an F for the course and their names will be forwarded to the Dean of Students. Physics 241, Exam 1 Equation Sheet N 2 ‘ 2 k=9-109 C”: k=4l so =9.1(I‘2 NC 2 1eV= 1.6-10“"J 6:16-10"? 71'8 m ¢=jE.fidA hid/4:9 szvb—Vaz— E-di dU=—17‘-df F=qE S S 80 a dv—fi-gu ~E-df v=£‘i V: 3‘1 Ex——d—V E “fl Ez——§—‘: qo r 1r“t ' dx y dy dz a I a! d 1 2 1 3:19: 1/:ij (3:9 C=80A V-Q— U=—g—=—QV=iCV2 Ar r v of 3A 2C 2 2 2 9 O J'cos(9)a’8:sin(6) Isin(9)d9=—cos(6) 3291 d—r=1n(r) jrd9=r9 r r r 2 r d = d =— J r I” I?“ F 2 Question 1 What is the magnitude of the electric field at point P? 1 2Q2 (a) 47:80 7 1 Q_2 d (b) 47:80 d2 (C) I JEQ ' _ 47:80 62 r—T—F I Q P W" 1 — 2 47580 d (d) (e)13 2 47:80 d Question 2 What is the electric potential difference at point P? a) 1 471780 d 1 9. (b) 427:80 d2 1 2_<22 (C) 47:60 0! 1 i 42:8G JEd 1 2 (e) Q 47:50 cl—2 (d) Question 3 In the diagram, which two points are closest to being at the same potential? (a) A and D (b) B and C (c) B and D (d) A and C (e) Potential is not defined here Question 4 A large negative charge —Q is located in the vicinity of points A and B. Suppose a positive charge +q is moved at constant speed from A to B by an external agent. Along which of the paths shown in the figure will the work done by the field be the greatest? (a) path 1 (b) path 2 (c) path 3 (d) path 4 (6) work is the same aiong all four paths. Question 5 The electric charge on a conductor is (a) uniformly distributed throughout the volume. (b) confined to the surface and is uniformly distributed. (c) mostly on the outer surface, but is not uniformly distributed. (d) entirely on the surface and is distributed according to the shape of the object. . (e) dispersed throughout the volume of the object and distributed according to the object’s shape. Question 6 In the figure, which best represents the field lines due to two spheres with equal and opposite charges? Question 7 Two identical conducting spheres, 1 and 2, carry equal amounts of charge and are fixed a distance apart that is large compared with their diameters (shown in part a). The spheres repel each other with an electrical force of F. Suppose now that a third identical sphere 3, having an insulating handle and initially uncharged, is touched first to sphere 1(shown in part b), then to sphere 2 (shown in part c), and finally removed (shown in part (1). Find the force between spheres l and 2 now. (a); (nil: «2»ng @ng (e) same F Question 8 The nucleus of an iron atom has a radius of 4 - 10'15m and contains 26 protons. What is the magnitude of the electrostatic force between two protons separated by one radius? (a) 1.410'6N (b) 14 N (c) 5.210'4N (d) 3.6102N (e) 3.6105N Question 9 Use Gauss’s Law to find the magnitude of the electric field at a point B a distance R from an infinitely long straight Wire. The wire has a uniform charge density 1. per unit length. P (a) E: 1 AR2 27:80 1 - R (b) E: 2E8 AR ' (c) E: 1 mm) 47580 1 A (d) E* 47580 R2 1 5L (6) E— 21:8 l1" Question 10 Find the electric potential due to a rod of lengthfl at point P, with uniform charge density 11 , as shown in the Figure. )1 471780 1 (b—a)/'L A (b) 42:80 62 77 z x9 2 ——-—+—m x (c) 1 33(9) ' “flag. (a) 1n(b/a) 47:80 a 1 M d ( ) 47:80 (b—a) l M (e) 47:80 (b ~— a)2 Question 11 A conducting shell carries a total charge of +4 LLC. A point charge A of +3 11C .is inside the shell; a point charge B of -2 [1C is outside the shell. What is the total charge on the outer shell of the conductor? (a) +2 itC (b) +1 tLC (c) +5 [1C ((1) -5 itC (e) +7 tLC Question 12 A plate carrying a uniform positive charge lies on the x—y plane away from the z-axis, as shown in the Figure. Which of the following graphs describes the electric potential on the z-axis? Note: The z—axis does not pass through the charge distribution. Question 13 Each side of a metal plate has a surface area of 0.1 m2. The total charge on the plate is +10 nC, or +5 nC on each surface. It is placed in a uniform electric field of 104 V/mgwith both surfaces perpendicular to the electric field. What are the final charges on each surface? Q (a) -9 nC +9 nC , l I (b) —9 HC +l9nC E. i (c) —4 nC +14 nC w_____, m, (d) —5 nC +9 nC (e) -3.5 nC +8.5 nC 1 ————-¥ ———-> plate Question 14 A flat sheet of paper of area 0.25 m2 is oriented so that the plane of the sheet is at an angle of 30° (as shown in the diagram) to a uniform electric field of magnitude 14 N/C. What is the magnitude of the electric flux through the sheet? (a) 3.0 Nm2/C (b) 1.8 Nm2/C (c) 0 Mr M (d) 3.5 Nm2/C _._? (e) 14 NmZ/C ___..,.. _______,_., Question 15 What is the equivalent capacitance of the circuit? (a) 2 pF (b) 6 ,uF I I ’22,; (0) 9m? Ml (d) 12m . (e) 24;”: - . ‘ - )1 ,5; F a 5,” F Question 16 A triangular conductor is placed in an originally uniform electric field. Which picture best represents the static eg uipotential lines near the conductor? Question 17 A point charge q is located a distance a from the center of a sphere of radius 2a. A charge Q is distributed uniformly throughout the volume of the sphere. What is the magnitude of the electrostatic force between the point charge q and the sphere? (a) F: 47:80 (611—? (b) F = (C) F 216711290 [ti—(22 (d) F 232%] El; (e) F: 36:38 (it—(3 Question 18 Find the magnitude of the electric field at the center of the square in the figure if q=8nC and a: 0.1m. (a) 3.6 . 103N/C. (b) 5.1 . 103N/C (c) 7.2 - 103N/C (d) 1.4 . 104N/C (e) 2.2 . 104N/C Question 19 A thin glass rod is bent into a semicircle of radius r. The rod has a uniform charge per unit length +1 on the upper half and - It on the low half. Find the magnitude of the electric field at B. (a) 0 22. (b) k; A (c) k——— 2r 4k 2» (d) ‘3‘: (e) 2k? Question 20 The electric potential varies along the x-axis as shown in the graph. Of the intervals shown, determine the interval in which Ex has its greatest value. (a) 15 V/m (b) 12 V/m '- (c) 7V/m E (d) 6V/m ,l. v (e) 3 Wm H‘- 7 II ‘ m an" ’ fl . E l allllll ' ...
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This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue.

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Ex1_F08 - Physics 241 Fall 2008 Exam 1 October 1, 2008...

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