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Unformatted text preview: Physics 2Ba quiz 4 solutions (Dated: February 6, 2009 18:08) Problem 1 The figure shows an electric field in space: Which of the following electric potential graphs best describes this field? The correct answer is A . The electric field is given by E =- V and since the electric field is uniform and points in the negative x-direction, it only has an x component. E x is negative and so the potential must have a positive slope since E x =- dV dx . Problem 2 In the circuit shown in the figure the capacitance C 1 is twice as large as the capacitance C 2 . Initially, the switch has been in position A for a long time. The switch is then flipped to position B. A long time after the swicthed is flipped, the charge in the capacitor C 2 A) is zero B) is equal to the charge in capacitor C 1 C) is half the charge in capacitor C 1 D) is twice the charge in capacitor C 1 E) none of the above The correct answer is C . You might be tempted to think that C 1 and C 2 are in series, but they are not since there is a net charge between the plates of the capacitors. They are in fact in parallel as they are connected across each other and therefore they have the same voltage. Denote the common voltage across C 1 and C 2 by V (note this will not be the same voltage as the battery). The charge that started on C 1 will now redistributed between the the capacitors after the switch is thrown. For each capacitor, the charge is Q 1 = C 1 V = 2 C 2 V (since C 1 = 2 C 2 ) Q 2 = C 2 V (1) 2...
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This note was uploaded on 03/28/2009 for the course PHYS 2b taught by Professor Schuller during the Winter '08 term at UCSD.
- Winter '08
- Electric Potential