142 Exam 1 Fall 2011 - NAME 2 A pair of parallel plates are separated by a distance of 0.050 m There is vacuum between the plates The plates are

142 Exam 1 Fall 2011 - NAME 2 A pair of parallel plates are...

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NAME: -a (T- 2. Apairofparallel platesareseparatedby adistanceof0.050m.Thereisvacuum betweentheplates.Theplatesareconnectedto avoltage source.Thevoltagedifferencebetweenthe twoplatesisunknown.A freeelectronat thecenterof theplateshas anaccelerationof2.813xl015m/s2.Hint:Ineachof thefollowing questionsyouwill needtocombineatleasttwodifferentprinciplesorexpressions. Nonecan besolvedin oneshot.a)Findtheunknown voltagedifferencebetweentheplates.Themassof theelectronis inyourhelppage.(10points)vssrrtrf/^'vsurfacecharge densityoneach plate.(10points) c)Findtheenergy densityof theelectricfieldbetweentheplates whenthesurfacechargedensityofeach plateis 2.(10points)O
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NAME: 3. For thecircuit showninFigure below,theammeterto the right ofpointAreads8.0 A andthecurrentflows from A to Bthroughthe 0.5 Qresistor.Thecurrentin theammeteron theleftis10.0A and flows from D to A. TheresistancebetweenD and A is1.0Q, and theresistance betweenA and C is 3.0 Q. The emf of thebatteriesareunknown.Thepolarityofthebatteriesare asshownin the figure(longer side representthehigher potential terminal.)Thecurrentin the3Qresistorisunknown (denotedby I) but itsdirectionisgivenas ahint.Thebatteriesand the
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