NAME ___________________________________PHY 2049 – Physics for Scientists and Engineers - IIDr, J. B. BindellFebruary 11, 1825OLD EXAMINATION #1Instructions: PRINT your name on EACH page of this examination. It is imperative thatyou are very clear in what you are doing. Use short descriptive sentences to state whatyou are doing. Be sure to show units in stated results. Carrying units through acalculation is often a good check of your work but not essential as long as they arecorrect at the end. Answers that cannot be read will be considered to be incorrect. Goodluck!Constants: k 8.99 x 109 Nm2/C208.85 x 10-12 C2/Nm2Problem #1 (40 points)In Figure 21-43, two tiny conducting balls of identical mass m andidentical charge q hang from non-conducting threads of length L.Assume that is so small that tan can be replaced by itsapproximate equal, sin which for small angles ~Using a free body diagram, find an algebraic expression for thedistance of separation “x”. Additional space has been provided onthe next page.1NAME ___________________________________(Problem #1 – additional space.)2NAME ___________________________________Problem #2 (30 points)(A WebAssign Question) An electric field given by E = 2.0 i - 3(y2 + 8.0) j pierces the Gaussian cube shown in the diagram. (E is in newtons per coulomb and x is in meters.) What is the electric flux through the following surfaces? (a) the top faceN · m2/C(b) the bottom faceN · m2/C(c) the left faceN · m2/C(d) the back faceN · m2/C(e) the net electric flux through the cubeN · m2/C 3NAME ___________________________________Problem #3 (30 Points)Recall that the electric field from an infinite sheet of charge was found to be .Consider an array of three infinite sheets of charge, all parallel to each other. Each of thesheets is perpendicular to the x axis. The x-coordinate for the three sheets and theircharge densities are a follows:SheetNumberx-coordinateElectric Field(FILL IN)1 -2,0 meters +2,0 C/m22 0 meters -2.0 C/m23 +4.0 meters -4.0 C/m2(a) Calculate and sketch a graph of the electric field in each of the four regionsindicated in the diagram. You can plot the graph directly on the diagram. Place theresults of your calculation directly in the table.(b) What would the force be on a 3C particle placed at x=3 meters?I II III IVx= -2 x=0
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