EXTRA CREDIT Electric Field and Forces c. The pin will move toward the top plate when the voltage is either negative or positive.

Transcription

1 EXTRA CREDIT T receive credit fr these questins, yu must input yur ansers n the LMS site. As, fr this set f questins, yu i be given ny ne pprtunity t prvide yur anser, s make sure yu have crrecty sved the prbem befre submitting yur anser. Sme questins have ny ne anser and sme have mre than ne r, at east, cud have mre than ne. The ay the questins are asked shud te yu hat is the case. 1. Eectric Fied and Frces A parae pate capacitr, ith fixed pates, is mdified as shn. A he is dried in the bttm pate and a bt is passed thrugh the he. A nut is screed nt the end utside f the capacitr making a pin ith a stp n either end f it. Thus, the pin is free t mve ang the directin indicated by the arr, but cannt mve fuy int r ut f the E fied regin f the capacitr. The high vtage surce driving the capacitr is sinusida, s that the tp pate aternates beteen a psitive and negative vtage. The bttm pate is grunded and the pin is eectricay cnnected t the bttm pate. ~ V(t) Which f the fing statements is true abut this cnfiguratin? a. There is n frce n the pin s it i nt mve. b. The pin i mve tard the tp pate hen the vtage is psitive and tard the bttm pate hen the vtage is negative. c. The pin i mve tard the tp pate hen the vtage is either negative r psitive. d. The pin i mve tard the bttm pate hen the vtage is either negative r psitive. e. The pin i mve tard the tp pate hen the vtage is negative and tard the bttm pate hen the vtage is psitive. Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009 1

2 . Sinky Inductr A sinky is used t create an inductr. A arge current is passed thrugh the ci. Since the sinky is very fexibe, the indings f the ci can mve if they experience any frce. Assume that the sinky is straight, ike the inductr shn at the right. Which f the fing statements are true abut this current-carrying inductr? a. There is n frce, s the shape f the sinky i nt change. b. The ength f the ci i increase. c. The ength f the ci i decrease. d. The radius f the ci i increase e. The radius f the ci i decrease. 3. Idea Parae Pate Transmissin Line A square crss-sectin parae pate transmissin ine is t be treated as idea. That is the equiptentias are a straight ines, as are the fied ines (n fringing). Assuming that the insuatr is a simpe dieectric ith permittivity, hich f the fing is true abut this ine? a. The characteristic impedance is Z b. The characteristic impedance is Z c. The characteristic impedance is Z d. The characteristic impedance is Z e. The characteristic impedance is Z 50 Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009

3 4. Resistance An dd experiment is perfrmed t determine the effect f cnductr shape n resistance. The shapes cnsidered are the 6 capita etters. The t eectrdes are fat and just tuch the tp and bttm f each etter, respectivey. Which f the fing statements are true? ABCDEFGHIJKLMNOPQRSTUVWXYZ a. The resistance f I is greater than the resistance f any ther ve. b. The resistance f E is greater than the resistance f F. c. The resistance f A is greater than the resistance f V. d. The resistance f R is ess than the resistance f P r I. e. The cmbined resistance f EE is greater than the cmbined resistance f ME. 5. Transmissin Lines Transients A 0V DC surce (battery), ith an interna impedance f 1 Ohm is cnnected t a 100m ng transmissin ine at time t = 0. The characteristic impedance f the transmissin ine is 50 Ohms and the vecity f prpagatin is u = x10 8 m/s. There is n ad n the ine (pen circuit). Which f the fing statements are true? a. The vtage at the ad is zer at time t = 0. b. The vtage at the ad is 0V at time t. c. The vtage at the ad is 9.8V at time t. d. The vtage at the ad is 9.8V at time t 500 ns e. The vtage at the ad is 19.6V at time t 500 ns 6. Transmissin Line Steady State Fr a sinusida vtage ave prpagating dn a ssess 50 Ohm transmissin ine, it is fund that 80% f the per prpagating tard the ad resistance is dissipated in the ad. This cud happen fr at east t different resistive ads. Fr hich f the fing i this be the case? a. RL 5 r R L 00 b. R L 333. r RL 75 c. R L 556. r R L 450 d. R L 8. r R L 897 e. RL 19 r R L Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009 3

4 7. Unifrm Pane Wave Prpagatin in Lssess r Lssy Media A unifrm pane ave (average per density = 1000 W per square meter) is incident nrmay n the bundary f a ssy medium fr hich the cmpex reative permittivity is r 8 j008.. What is the apprximate refected per density and the per density absrbed as heat in the ssy medium? That is, hich f the fing ansers is the csest t the actua ansers? a. S 700 W refected m and S 300 W absrbed m b. S 337 W refected m and S 663 W absrbed m c. S 8 W refected m and S 77 W absrbed m d. S W m and W refected 400 S absrbed 600 m e. S W m and W refected 300 S absrbed 700 m 8. Magnetic Circuit A magnetic circuit is cnfigured as shn. A egs f the circuit are frmed using square crss-sectin magnetic cre materias. N turns f ire are rapped arund eg. The permeabiity f the vertica egs v is nt the same as the permeabiity f the hriznta egs h. A vertica egs have the same dimensins as d a hriznta egs Which f the fing statements are true? a. The magnetic fux in eg is equa t the magnetic fux in eg 6 and eg 7. b. The magnetic fux in eg 1 is equa t the magnetic fux in eg 5. c. The tta magnetic fux eaving any nde in the magnetic circuit is zer d. The magnetic fux in eg 1 is three times the magnetic fux in egs 3, 4 and 5. e. The magnetic fux in eg 3 is equa t the magnetic fux in eg 5. Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009 4

5 9. Materia Prperties and Pane Waves A arge sab f materia is cnfigured using a magnetic insuatr. That is, the materia is a gd insuatr, but as has magnetic prperties. Fr the purpses f this prbem, e i assume that the sab is infinitey thick, s e d nt have t be cncerned abut refectins ff f the back surface. The permeabiity is and the permittivity is. The frmer can be up t 1000 times greater than free space hie the atter can be up t 10 times greater, fr this prbem. Fr a questins, assume there is sme kind f materia in regin s that ny regin 1 is free space. E x H y z Which f the fing statements are true? a. The intrinsic impedance f regin (the sab materia) is aays b. The intrinsic impedance f regin (the sab materia) can be either r, but nt. c. The intrinsic impedance f regin (the sab materia) is aays d. The intrinsic impedance f regin (the sab materia) can be either r. e. The intrinsic impedance f regin (the sab materia) can be 30 times greater than. 10. Sving Lapace s and/r Pissn s Equatins A spherica she f unifrm surface charge density s is cated at r a. This charge is surrunded by a fating cnducting she in the regin a r 3a If the vtage is referenced t zer at r, hat is the vaue f the ptentia at the rigin r = 0? sa a. 3 7sa b. 9 Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009 5

6 c. d. e. 5sa 6 sa 6 sa Using Ampere s La t find Magnetic Fieds An infinitey ng, straight, cyindrica ire, diameter = a, carries a current I. Which f the fing statements are true? a. The magnetic fux density B is zer n the axis f the ire. b. There is n magnetic fux inside the ire. c. The magnetic fux per unit ength inside the ire is nn-zer and finite. d. The magnetic fux per unit ength utside the ire is infinite e. The magnetic fux per unit ength utside the ire is nn-zer and finite f. The magnetic fux utside the ire is zer 1. Faraday s La A sing set is cnstructed f meta as shn be. The chains that hd up the seat are as meta. Assume that the persn in the sing has a vtmeter in their ap (that can measure bth AC and DC) cnnected t the ends f the chains here they attach t the seat. The chains as make gd eectrica cntact t the hriznta pipe frm hich they are suspended. Which f the fing statements are true? a. The vtage seen i aays be zer. b. The vtage seen can never be zer. c. The vtage i be peridic in time and sma. d. The genera directin f the earth s fied can be determined by nting hether the vtage is increasing r decreasing hie singing frard r backard, respectivey. e. The intensity f the vtage i vary ith the directin f the hriznta pipe (shn ith the arr abve). f. The intensity f the vtage i nt vary ith the catin f the sing. Fieds and Waves I Extra Credit Fa 009 K. A. Cnnr December 009 6