Solution sample final - Problem 1 a) Find the current in...

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Problem 1 a) Find the current in each resistance in the circuit below, the battery has negligible internal resistance (10 points). b) If the battery is replaced by a charged 1F capacitance what fraction of the charge will remain after 1 sec (10 points)? 3 6v 2 4 2 a) The three resistances are in parallel. The effective resistance R e is 1111 0.8 224 e e R R =++ = Ω The total resistance of the circuit = 3+0.8 = 3.8 The current from the battery and through the 3 resistance is given by 6 1.58 3.8 e V I A R ε == = The potential V across each of the parallel resistances is the same and by Kirchoff’s voltage law is 1 6 1.58 3 1.26 VI R V =− ×= The current through each 2 resistance is thus 1.26 0.63 2 V A = And through the 4 resistance is 1.26 0.32 4 V A = b) The charge as a function of time is given by 0 t RC QQ e = The resistance in the time constant is the equivalent resistance of the whole circuit =3.8 The time constant RC=3.8 s The fraction of charge remaining after 1 sec is 1 3.8 0.77 = e
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University of Minnesota School of Physics and Astronomy Physics 1302, Spring 2007 Final Examination: Multiple Choice Problems 1. What is the energy stored in an electric field of magnitude 1.0 x 10 5 V/m that uniformly fills a cube 10.0 cm on a side? (a) 0.47 x 10 -5 J (b) 0.96 x 10 -5 J (c) 1.3 x 10 -5 J (d) 4.4 x 10 -5 J (e) 8.3 x 10 -5 J 2. A loop of wire is placed in the horizontal plane in a magnetic field. The field points vertically upward and the magnitude of the field is increasing at a uniform rate. Which of the following statements is true?
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Solution sample final - Problem 1 a) Find the current in...

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