Sample Exam 5 - Skip Problems 1-3

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1 Smple Exm 5 - Skip Problems 1-3 Physics 121 Common Exm 2: Fll 2010 Nme (Print): 4 igit I: Section: Honors Code Pledge: As n NJIT student I, pledge to comply with the provisions of the NJIT Acdemic Honor Code. I ssert tht I hve not violted the NJIT Acdemic Honor Code. Instructions: First, write your nme nd section number on both the Scntron form nd this exm question book. There re 18 multiple choice questions on this exm, ll worth the sme mount. Sixteen nswers correct yields score of 100%. Questions 17 nd 18 my be hrder thn the others. For most problems tht require clcultions you need should show how you got your nswers on this exm book, using the bck if needed. Instructors my ssume tht nswers with no work re rndom guesses nd indicte no understnding. Circle your choices on the exm pper nd lso nswer ech question on the Scntron crd using #2 pencil. Use the formul sheet (lst exm pge) nd no other informtion sources of ny kind for reference. It is the sme s the one mde vilble on the course web site. Clcultors re llowed but shring is not. If you hve questions or need something cll your proctor or instructor. As you know, NJIT hs zero-tolernce policy for ethics code violtions. Turn off ll cell phones, pgers, or similr electronic devices. 1. A point chrge of 10 nno-coulombs is locted t the center of cube. Ech of the six fces of the cube is 25 cm. by 25 cm. in size. Wht is the totl electric flux through the surfce of the cube? A) 8.85 x N m 2 /C B) 1130 N m 2 /C C) 188 N m 2 /C ) 0.0 N m 2 /C E) 94.2 N m 2 /C 2. The circulr surfce shown in the sketch hs rdius of 10 cm. It is immersed in uniform electric field with mgnitude 120N/C. The field lines mke 45 o ngle with the vector norml to the surfce, s shown in the sketch. Wht is the electric flux through the surfce in N.m 2 /C: A) 7.1 x 10-3 B) 2.7 C) 3.8 ) E) o E 3. A positive chrge Q = 25 nc is plced inside the cvity of n egg shped, electriclly neutrl conducting shell s shown. How much chrge will be induced on the inner nd outer surfces of the shell? A. Q inner = 25 C. Q outer = 0 C B. Q inner = 0 nc. Q outer = +25 nc C. Q inner = -25 nc. Q outer = 0 C. Q inner = - 25 nc. Q outer = +25 nc E. Q inner = 25 nc. Q outer = -25 nc Q Pge 1 of 7

2 4. Four point chrges re locted t the corners of dimond-shped prllelogrm s shown in the sketch. The vlue of Q = 20 µc. The length of ech side of the figure is = 30 cm, with n 60 0 ngle locted s shown. The potentil t infinity is the zero reference level. Find n expression for the electric potentil V t point P, the center of the dimond shpe. Note: k e is the constnt 1 / 4πε 0 A) V = 0 B) V = 2k e Q /.sqrt(3) C) V = -4k e Q / ) V = -k e Q /.sqrt(3) E) V = -2k e Q / +Q - 2Q P -2Q +2Q 5. Find the electric field 0.3 cm wy from n infinitely long thin chrged line with liner chrge density λ = 2.0 µc/m. A. 12 x 10 6 V/m B. 12 x 10 7 V/m C. 4.5 x 10 5 V/m. 9 x 10 9 V/m E. 4.5 x 10 6 V/m 6. The equi-potentil surfces ner n infinite chrged sheet re plnes. If the potentil difference between pir of equipotentils tht re 8 meters prt is 1200 volts, wht is the mgnitude of the electric field between the sheets? A) 1.7 x 10-3 V/m B) 300 V/m C) 150 V/m ) 2400 V/m E) 1.7 x V/m Pge 2 of 7

3 7. A metl sphere is chrged to potentil of 300 volts. Its rdius is 2 meters. The potentil t point 1 meter from the center of the sphere is: A) 300 V. B) -100 V. C) 300 V. ) 0 V. E) 100 V. 8. An electron is moved through displcement x prllel to the direction of uniform electric field. uring this displcement: E A) the potentil energy of the electron nd the electric potentil do not chnge. B) the potentil energy of the electron increses, the electric potentil increses. C) the potentil energy of the electron increses, the electric potentil decreses. ) the potentil energy of the electron decreses, the electric potentil decreses. E) the potentil energy of the electron decreses, the electric potentil increses 9. The cpcitor in the sketch hs cpcitnce of 24.0 µf nd is initilly unchrged. The bttery mintins potentil difference of 3.0 V. How much totl chrge flows out of the bttery until the cpcitor is fully chrged (the current stops flowing)? A) 3.20 µc B) 8.00 µc C) 72.0 µc ) 12,000 µc E) 30.0 µc 10. A prllel plte cpcitor being designed is supposed to hve cpcitnce of 400 pf (1 pf = F = 10-6 µf). It will be filled with mteril whose dielectric constnt is close to 1.5 (glss). The distnce between pltes will be 0.3mm. Approximtely, wht should the re of the pltes be? A) 1.10 m 2 B) m 2. C) m 2. ) m 2. E) 0.9 m 2. Pge 3 of 7

4 11. Three cpcitors re connected in the series/prllel rrngement shown in the sketch. Suppose C 1 = 30µF, C 2 = 30µF, nd C 3 = 15µF. The potentil difference cross the combintion V b = 40 V. The equivlent cpcitnce between points nd b is closest to: b C 3 C 1 A) 15 µf B) 30 µf C) 7.5 µf ) 45 µf E) 12 µf C In problem 11, clculte the voltge cross cpcitor C 2 (in volts) A) 60 B) 40 C) 10 ) 20 E) 6x Two wires mde of the sme mteril re joined end-to-end nd potentil difference is mintined cross the combintion, from to b in the sketch. The thin wire hs cross sectionl re A/3 nd length L. The ftter wire hs re A nd length 2L. Which of the following quntities re the sme for both wires: 1. The resistivity of ech wire 2. The resistnce of ech wire 3. The current density inside ech wire 4. The current through ech wire 5. The potentil difference cross ech wire 2L Are A L b Are A/3 A) 1, 2, nd 3 B) 1, 2, 4, nd 5 C) 1 only ) 2 only E) 1 nd 4 only Pge 4 of 7

14. In the circuit shown in the sketch, switches S 1 nd S 2 re initilly open. Cpcitor C 1 = 30.0 nf is then chrged by closing switch S 1 which connects it to the bttery whose EMF E = 90 V.

5 14. In the circuit shown in the sketch, switches S 1 nd S 2 re initilly open. Cpcitor C 1 = 30.0 nf is then chrged by closing switch S 1 which connects it to the bttery whose EMF E = 90 V. Switch S 1 is then opened, thereby disconnecting C 1 from the bttery. Switch S 2 is then closed, thereby connecting the chrged cpcitor C 1 to the unchrged 15.0 nf cpcitor C 2. Find the finl potentil difference cross cpcitors C 1 nd C 2. (Hint: fter being disconnected, the totl chrge on the combintion C 1, C 2 remins constnt). E A. 60 V B. 30 V C. 4 V. 10 V E. 120 V 15. For the previous problem, the finl chrge on cpcitor C 1 is closest to: A) 2.0 µc B) 0.8 nc C) 0.2 µc ) 1.2 nc E) 1.8 µc 16. Assume tht the btteries in the figure hve negligible internl resistnce. Assume tht the current flows counterclockwise. Find the mgnitude of the current in the circuit nd the power dissipted in resistor R 1. A) i = 0.67 A, P 1 = 2.7 wtts B) i = 1.33 A, P 1 = 5.4 wtts C) i = 1.5 A, P 1 = 24 wtts ) i = 0.67 A, P 1 = 1.8 wtts E) i = 1.5 A, P 1 = 9 wtts E 2 = 8 V E 1 = 16 V Pge 5 of 7

6 Extr Credit: 17. The sketch shows edge views of two prllel conducting sheets with identicl positive chrges Q = 4 µc. on ech. The re of ech plte re is 2 m 2. Wht is the electric field E IN midwy between the pltes; lso, wht is E P t point P, which is 1 mm bove the upper plte s shown? Hint: The dshed line Gussin surfces my be helpful. A) E IN = 0, E P = 5.65 x 10 4 V/m B) E IN = 0, E P = 2.26 x 10 5 V/m C) E IN = 1.1 x 10 5 V/m, E P = zero ) E IN = 0, E P = 1.1 x 10 5 V/m E) E IN = 0, E P = 0 P d d 18. The figure shows plstic rod of length L = 2.5 m, with non-uniform liner chrge density λ = α x with α=10-3 C/m 2. The rod is lying on the x xis. Assuming V = 0 t infinity, find the electric potentil (in volts) t the left end of the rod in other words, t the origin. Select the closest nswer. A) Zero B) 2.7 x volts C) 2.25 x 10 7 volts ) 1.35 x 10 8 volts E) Infinity Pge 6 of 7

7 ANSWER KEY: Fll 2010 Physics 121 Common Exm 2, Version 1. B 2. B E 5. A 6. C 7. A 8. C 9. C B E 14. A 15. E B 18. C Pge 7 of 7

Physics 121 Sample Common Exam 1 NOTE: ANSWERS ARE ON PAGE 8. Instructions:

Physics 121 Sample Common Exam 1 NOTE: ANSWERS ARE ON PAGE 8. Instructions: Physics 121 Smple Common Exm 1 NOTE: ANSWERS ARE ON PAGE 8 Nme (Print): 4 Digit ID: Section: Instructions: Answer ll questions. uestions 1 through 16 re multiple choice questions worth 5 points ech. You