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Physics 224 - Test #2 March 2, 2009 Name___________________________________________________ Total Problem 1: _____________/25 Total Problem 2: _____________/25 Total Problem 3: _____________/25 Total Problem 4: _____________/25 Total Problem 5: _____________/25 Total Problem 6: _____________/25 Total Points:__________________________/125 Percentage Score: ______________________ % ***You will answer only 5 of the 6 problems for exam credit; your choice. All problems require you to show all the steps in obtaining the answer or to provide clear and complete descriptions/explanations. This includes, but is not limited to, defining all variables, showing the equations to be used, explaining a concept and including units with all values listed. All problems are worth up to 25 points each. Good Luck!!!! **In addition, the sixth problem may be completed for extra credit! Please be sure to indicate which one of the problems you're using for extra credit.....otherwise the five lowest scored problems will be used to determine your grade and you will NOT receive extra credit for the remaining problem!! 1) Shown below is a DC circuit that contains two switches. Each switch is resistance-less when closed. All of the connecting wires should be considered to have zero resistance. All of the resistors shown are identical. The circuit contains an ideal ammeter (A) used to measure the current in the circuit. The diagram shows the switches open. Below the diagram are four different switch configurations for the circuit. Of the switch configurations shown, which one will produce the largest reading on the ammeter? 2) The following diagrams show three separate situations involving charges on metal spheres that are initially in contact. The positively charged rod is brought up to the same distance from each set of metal spheres. The spheres are then separated simultaneously from each other using the insulating handles. Finally the charged rod is removed. After the rod is removed which rank the spheres from most positive to most negative? 3) The capacitor in the figure has a crosssectional area Ao and a distance between plates y. The thickness of each metal plate is t. A battery with voltage Vo is connected across the plates of the capacitor. There is nothing between the plates of the capacitor. For each modification listed below, state whether the capacitance increases, decreases, or remains the same. Modification 1. Increase the distance y 2. Increase the area Ao 3. Increase the plate thickness t 4. Insert a dielectric material between the plates 5. Increase the battery voltage Vo Effect on capacitance Increases Decreases Remains Same 4) Two equal and opposite charges are fixed in space at the locations shown. Seven points are labeled A - G in the vicinity of these charges. For each pair of points, decide whether the electric potential at point 1 is greater than, less than, or equal to the electric potential at point 2. Assume that the electric potential is zero far away from the charges. Point 1 Point 2 A C A B A D A F A E B C B D B E F G D E Electric Potential (> or < or =) Explanation 5) In each case below, small charged particles are fixed on grids having the same spacing. Each charge q is identical, and all other charges have a magnitude that is an integer multiple of Q. Rank the magnitude of the force on the charge labeled q due to the other charge(s) in its grid. Be sure to illustrate the force vector(s) on q as part of your explanation. 6) Using loop and junction rules only, list all the possible associated current and voltage equations related to the figure below. BONUS: If both batteries are 1 V and all of the resistors are 1 W. What are the unknown currents in the problem above?