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Unformatted text preview: Physics 2B Quiz 2 Summer Session I 2009 Version 0 Name: PID: Quiz ID: READ FIRST: Make sure to write/fill in your scantron form your name, quiz ID and the test version. e 1 . 6 10- 19 C , k 9 . 10 9 Nm 2 / C 2 , 8 . 9 10- 12 C 2 / Nm 2 , Z dx x- a = ln | x- a | Unless otherwise specified, assume potential is zero at infinity. 1. An electron move in the- x direction 0 . 5m through an electric field ~ E = 2 . 5 x N / C. What is the change in potential energy? Solution: The potential difference is: V =- ~ E ~ l = 1 . 25V. An electron carries charge- e , So the change in potential energy is U = q V =- 1 . 25 eV. A. -1.25 eV B. 1.25 eV C. 1.25 J D. -1.25 J 2. At each of the four corners of a square is a 2 nC charge. The side of the square is 1.41 m. What is electric potential at the center of the square? Solution: The center is the same distance away from each charges: 1 . 41 / 2 1 (m). Calculate the potential using principle of superposition: = 4 kq d 4 9 10 9 J m C 2 2 10- 9 C 1m = 72V A. 72 V B. 36 V C. 18 V D. 144 V 3. How much energy is needed to assemble four 2 nC charges to form a square of side 1.41 cm? Solution: Each charge see three other charges: two at distance 1.41 cm, one at distance 2 cm. So the total energy is just four times the energy to move the last charge in placewith the factor of 1 / 2 to take into account double-counting.2 to take into account double-counting....
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This note was uploaded on 07/26/2009 for the course PHYS 2b taught by Professor Schuller during the Summer '08 term at UCSD.
- Summer '08