Phy 102 2010 Exam 1

Phy 102 2010 Exam 1 - nremerlglolng Physics 102 Exam 1...

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Unformatted text preview: nremerlglolng Physics 102 Exam 1 February 8, 2010 Dr. Sharon T. Zane I In order to obtain full credit for problems 16 and 17, you must show your assumptions and work clearly and iegibly. They are worth 20 points each. For problems 1—15, place your letter answer on this sheet below. Problems 1-15 are worth 4 points each. You may be asked to show your photo ID. upon submitting the exam. .. r - a (9 , ‘- MC 1:116]? “ XL gfifihocl “A "g. - Qr~—’—l—‘—'_"L_'_> Jr “7L 5‘ . "L Q :- ffiflq—fl O “(0‘0 1)"? 1." MC V L'lmo'gt) 1. Two point charges of magnitude + 7.00 11C and - 9.00 11C are placed along the x- : axis at x= 0 cm and x= 40.0 cm, respectively. Where must a third charge , be .9 ( 9W0 3 placed along the x-axis so that it does not experience any net force because _of the \) a)0200m b)2.99m (m d)-2.99m e)0.187m 2. The equipctential surfaces between the two point charges are shown 1n the figure below with the value of potential marked for each line. If the distance between points A and B is 2.5 cm what is the intensity of the electric field between these two points? 9 31%;: 2v KW 1.6V 1.4V /1.2v /1.ov /aav [\gw“ @6 Wm A 3 f /' ! Vim g 10 Wm ‘39) ‘3‘ ,3“ : ”EL“ {1“ at x \M g 3. A parallel plate capacitor with plate separation of 4.0 cm has a plate area of 6.0 X 10 2 m2. What IS the capacitance of this capacitor if a dielectric material with a [5 Q OK dielectric constant of 2. 4 IS placed between the plates? -12 -14 -14 n :9}. - Eels ’ a)3.7><10 F 3.?X10 F c)16><10 F 1v \l'fl'q N” d)32><101“F 2X10'12F (X 1' \f V“ e 4. A styrofoam ball of mass 0.120 g is placed 111 an electric field -' \f 9 pointing downward. What charge must be placed on the ball for 1 . _ - a) -16.0 nC b) -l8.0 nC c) -57.2 nC d) -125 nC @196 nC .oUt‘N' G; U C 5. You are given a copper bar of dimensions 3 cm X 5 cm x 8 cm and asked to attach Cl” \3 leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure a) cmXScm. b)3cm><80m. c)50m><8cn1. G000: -—--~ Any pair of faces produces the same resistance. £0 L” .. ”LO .— \/L—F-1<'/ZI __ _- N ll... __ l % [EC \ l: ._ Q3000 1" __ 19L l {0001 Jr ‘2 t lfll : ‘3‘}, _ jjlir- . - 11’ ‘ 1.. ‘5‘ / Y _.... \ | “A if” ‘5 r liar 41" 1, riff... 3%" Q . 9 - 1 flaw firm 2/1614 «nuns itfi‘i‘uto H" v, «cw-7mm... w"-N.---°~2w-rtwaw-twwmmwuqm-mww — mm 6. The figure below shows four Gaussian surfaces surrounding a distribution of charges. Which Gaussian surfaces have no electric flux through thern? y '7. 1%.ch moved from a negative to a positive plate of a parallel plate - W W .. W W... W 9‘ difference between p s offlns c 'a)5ov b)81V c)ssv d)23V ' 0v 5‘ 8. 'I‘wopointcharges,initially2.00mapart,experiencea1.90-Nforce Iftheyare % “a mgfimumsepamflmmwhatistheelecnicmenthem? j” 1 9. Acapacitor consists ofasetoftwo parallel plates ofsreaAseparatedbya distanced. Thiscspacitorisconnectedtoabaflerythatmaintainsaconstantpotenfial difference between the plates. Ifthe een the lates led, the E» ‘66 ' magnitude of the electrical cum stored on the camitor will CIT-1f ' a)doub1_e. b) quadruple. ' c)becutinhalf. mammalian. e) not change. _ - _ I \ V 10. _Anegativecharge, iffree, triestomove @h mhigh potmtialto low potential. @from low potential to high potential. c towardinfinity. )awayfi-ominfinity._ ' e)’ in the direction of the electric field. 11. The lines of the electric field will contact a conducting surface 'panlleltothemn'fsce b)ata45° angletothesurfaceduetc symmetry. c)’Iheydonotcontactfliesurface,butarebentawayfiomit. ' d)i1trightanglestcthesurface. -e)noneofthese Y) I. \ .. ' Y1 \10' \uo \. _J ”H"... 12. The tun sten lament of a light bulb has a resistivi lp = 5.6 xltl‘8 Q - m. If the filament i 27 cm long, what is the resistance of afimbbfiéfitmg at the" standard ho 'sélfilH—vo tage of 120 V when lit (hot . .;_ a) 1.2 Q b) 144 9 c) 120 Q ‘ ' d) none ofthese " 13. What is the diameter of the tungsten filament of problem 12? (3)12 11111 b) 5.8 1.1m c) 33 pm d) 0.11 nm 1. 14. The danger(s) of a grain silo is(_are) [attendance question] a) the dust is flammable b) the dust is explosive c risk of suffocation d) the dust is poisonous c) all of these a, b, and c 15. The radius of the second Bohr orbit of the hydrogen atom is r2 = 2.1 16 x1 0'10 m . The speed of an electron in this orbit is f ' a) 1.20x1012mls .7.47x103°mls c)1.09x106mls d) 2.18x106mfs e)noneofthese -8 __‘ KL 1 K, \Q’ g ‘1’ J \ , LVO "I, - \9 w- 0 I O J." '11 dwkljrw (L3 {:22 Q1 _ \Jt {9/ l>< '00 " —-/ Qv —, {LO \ a%\t’z’fijcm it \3: , , a 5.653.”) ’ , ’3, 3 SWJQL’L’J‘ L (‘3’ a ‘1’ iLiUl-r' P.‘ ‘11!“ iW/u' V1; ’ o .. .49. 1 7:1“) ., 3’ Q " \0 Q" 9, b‘tfiw .. Li I) “1Q <3 w“? " \uu :: / \ 1,34) q ’4 /q, lulu lav)” \yhl \f- 2 .--—d- [L :‘YLK'L \‘T— j- Q— P?- : a 04‘0 (FL __ “1 lFZ-o’}: I 1093-1 :- TL (3 _o\ 1’ 1'0” 11: l?— (:S'1%lFL-ullf; rLQ’iVJ 11* —Q r) - Ill-SCH“O 16. Three point charges of values +1.0 C, +2.0 C, and +3.0 C are located at the corners of an equilateral triangle of sides 1.0 m. It is desired to find the work required to move these charges inward to the corners of an equilateral triangle of smaller side 0.50 m, centered the same as the larger triangle (see diagram). a). Calculate the potential energy of the three charges at the comers of the larger triangle. +1 0 C b). Imagine the charges having moved in to the corners of the smaller triangle and calculate the potential energy of this new configuration. c). How much work was required by some +2.0 C I +3 0 C external agent to move these three charges ' inward to the smaller triangle? 1.: ML: 17. The electric field between the plates of a parallel-plate capec' ishorizontal, uniform, and has a magnitude E. A sm bject with a charge 0 4. 00 MC )1; attached to string. The tension in the string is .75 ,and the angle it makes with the vertical IS f. 0° . 014 N1 _ mass (- W W O m an Old W a) What is the ghaI’g'e of the object? M3 M b) What IS the magnitude of the electric field? ..-—---'"" ...
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