final3-sum11 - August 5, 2011 PHY 2049 Summer 2011 Final...

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August 5, 2011 PHY 2049 Summer 2011 Final exam 1. In the circuit shown all capacitors are 4.0 μ F and the power supply is 12V. The potential drop (in V) across the capacitor labeled q is: (A) 4.8 (B) 12 (C) 3.6 (D) 7.2 (E) 20 The lower branch is directly across the battery and therefore is subject to the full potential difference. Its equivalent capacitance is 2.4 μ C. The charge on the first capacitor is then 2.4 X 12 = 28.8 μ C . The potential difference across the first capacitor is 28.8/4 = 7.2V. The potential differnce across q then is 12 -7.2 = 4.8V. 2. In the multi-loop circuit shown, the current through the 2.0k resistor is (in mA) (A) 1.2 (B) 0.4 (C) 2.4 (D) 0.8 (E) Not enough information Suppose that the currents in the left and right branches are I 1 and I 2 , both in mA and going up. Through the middle branch, it must be (I 1 +I 2 ) in mA and going down. The loop on the left gives 6 – 6I 1 – 2(I 1 +I 2 ) = 0. The loop on the right gives 6-6I 2 – 2(I 1 +I 2 ) = 0. Add the two equations and you get, 12 – 10(I 1 +I 2 ) = 0 or (I 1 +I 2 ) = 1.2A. 3. A non-uniform electric field given by ~E = (5.5ˆi - 2.1ˆj + (4.6z 2 - 3)ˆk) N/C pierces a cube with sides 3 m, as shown in the figure. The cube has its rear corner at the origin. What is the total charge inside the cube? (A) +3.3 nC (B) -3.3 nC (C) +1.5 nC (D) -1.5 nC (E) None of these A cube has sides with normals along the Cartesian axes. The total flux being the same on the sides with normals along x and y (except for their signs) will vanish. Only the sides up and down will contribute and they give, Φ = q/ ε o = 3 2 [4.6x3 2 ] ==> q = 3.3 nC. 4. The capacitances of the four capacitors shown in Fig. 25-52 are given in terms of a certain quantity C . In ratio to C, what is the equivalent capacitance between points A and B ? ( Hint: First imagine that a battery is connected between those two points; then reduce the circuit to an equivalent capacitance.).
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(A) 0.82
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This note was uploaded on 12/05/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.

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final3-sum11 - August 5, 2011 PHY 2049 Summer 2011 Final...

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