Physics 313 Practice Test Page 1. University Physics III Practice Test II

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1 Physics 313 Pactice Test Page 1 Univesity Physics III Pactice Test II This pactice test should give you a ough idea of the fomat and oveall level of the Physics 313 exams. The actual exams will have diffeent questions and poblems, and may cove a diffeent selection of topics. Individual questions and poblems on the actual exams may be eithe hade o easie than those in this pactice test. Assume that all numbes ae significant to 3 figues. Fomulas and constants: F = qe E = 1 4"# 0 Q 2 ˆ E da = q enc # k = 1 Nm 2 = 8.99 $10 9 4"# 0 C 2 " 0 m electon = 9.11"10 #31 kg e = q electon =1.60 "10 #19 C "V = # $ E d s V = " k dq Q = VC V = IR U = 1 2 Q "V P = IV E = " #V ˆ i " #V ˆ j " #V k ˆ #x #y #z

2 Physics 313 Pactice Test Page 2 1. A thin, unifomly chaged ing of adius R and total chage Q is in the xy-plane, centeed on the oigin as shown. Point P is located on the z axis at (0, 0, z). (a) By diect integation, find the potential V (0,0,z) at point P as a function of z. y dq x R P (0, 0, z) z (b) Using the potential function V (0,0,z) that you found in pat (a), detemine the components of the electic field E (0,0,z) at point P.

3 Physics 313 Pactice Test Page 3 (2) (a) I build 4 cicuits (A, B, C, and D) out of esistos and capacitos as shown. These cicuits ae all built out of identical capacitos and identical esistos, but I don t know the specific values of R and C. At t=0, a potential V is put acoss each of the cicuits (sepaately) and held fo a long time. Ae the following statements Tue o False? At t = 0, the initial cuent though one of the esistos in cicuit C is half the cuent though the esisto in cicuit A. The final chage on each of the capacitos in cicuits A and C will be the same. The final chages on the individual capacitos in cicuit D will be 3 times that of cicuit A. Ultimately, the potential diffeence acoss each individual capacito in cicuit C will be 3 times the potential acoss each capacito in cicuit D (b) A seies RC cicuit is made up of a 200. µf capacito, a 400. kω esisto and a 12.0V battey with an intenal esistance of 10.0 kω. At t =0.00 sec, a switch is closed, completing the cicuit and stating to chage the (initially unchaged) capacito. (i) Calculate the initial teminal voltage of the battey. (ii) How many seconds does it take fo the instantaneous powe dissipated by the esisto to fall to 50.0% of its initial value?

4 Physics 313 Pactice Test Page 4 (3) (Pat 1) The following ae actual answes given by Physics 313 students. Wite the lettes of the sentences that coectly explain why chage is unifomly distibuted on the oute suface of an isolated spheical conducto. (Note: GL stands fo Gauss s Law) A. Due to GL the chage cannot be contained within the gaussian suface. B. GL says the chage enclosed must equal zeo, and it is evenly distibuted since the chages epel. C. Because it is static, chage cannot move, and the fathest away fom each othe the chage can get is on the suface. D. Conductos distibute chage evenly. E. GL says E = 0 since othewise the conductos would spead the chage and would no longe be electostatic. F. Like chages epel, pushing the chage though the whole of the mateial. G. The electic field inside the metal must be zeo, and the chage is evenly distibuted. H. Because the total chage inside is zeo. The gaussian suface on the inside pushes the chages to the suface. I. GL says so! J. Since like chages epel, and electons move feely in a conducto, the chages move as fa fom each othe as possible. K. If it wee not evenly distibuted, thee would be a epulsive foce and E would not be zeo. (Pat 2) A 10 µf capacito is chaged by connecting it to a 12 V souce. A 20 µf capacito is sepaately chaged to 15 V. (a) Calculate the chage on each capacito and the enegy stoed in each capacito. The capacitos ae now disconnected fom thei souces and connected to each othe with positive plate to positive plate, and negative plate to negative plate. (b) Find the effective capacitance of this combination. (c) Detemine the potential diffeence acoss this combination. (d) What is the total enegy stoed in this combination? (e) Suppose the expeiment is epeated but the capacitos ae instead connected positive to negative and negative to positive. How do you expect the answes to pats (c) and (d) to change and why?

5 Physics 313 Pactice Test Page 5 (4) Fo the following cicuit, find the thee cuents i1, i2, i3. Use the cuents as defined on the figue. Calculate V a V b. PART II ON NEXT PAGE

6 Physics 313 Pactice Test Page 6 1b. Each of the esistos below has a value of 150 Ω. What is the effective esistance of the cicuit?

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