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Unformatted text preview: Solution for Homework 9 Computing Potential Difference Solution to Homework Problem 9.1(Direction of Charge Moving in a Potential) Problem: A positive charge is place at the point A in the figure at the right. Select the direction the charge will move if released at point A . Select One of the Following: (a) + x (b) x (c) + y (dAnswer) y (e) The charge will not move. 10V 3V 1V A x y Solution A positive charge will move to lower potential and will therefore move in the y direction. Total Points for Problem: 3 Points Solution to Homework Problem 9.2(Work Along Various Paths) Problem: Refer to the figure below. Which path, 1 , 2 or 3 , from point A to point B requires the most work to move a + Q charge from A to B ? Select One of the Following: (a) Path 1 (b) Path 2 (c) Path 3 (dAnswer) They all require the same amount of work. 1 +Q +Q 1 2 3 B A Solution (d)  They all require the same amount of work. The energy of the system changes by the same net amount in any case. Electric potential is path independant. Total Points for Problem: 3 Points Solution to Homework Problem 9.3(Velocity of Electron Escaping Hydrogen) Problem: An electron and a proton are on average 5 10 11 m apart in a hydrogen atom. Suppose (disasterously) the electrons charge changed sign and the atom blew apart. The charge of an electron is 1 . 6 10 19 C and the mass of an electron is 9 . 11 10 31 kg . How fast would the electron be going after it was very far from the proton. You may assume the proton is stationary. Neglect any relativistic effects. Select One of the Following: (a) 3 10 8 m s (bAnswer) 3 10 6 m s (c) 9 10 12 m s (d) 4 10 18 m s (e) 4 10 3 m s Solution 2 The potential energy of the electron/proton system is the work to assemble it, U = q V = kq 2 r = k (1 . 6 10 19 C) 2 5 10 11 m = 4 . 61 10 18 J All this potential energy is converted into kinetic energy once the electron is far from the proton. U = 1 2 mv 2 or solving for the velocity v = radicalbigg 2 U m = radicalBigg 2(3 10 6 m s ) 9 . 11 10 31 kg = 3 10 6 m s Total Points for Problem: 3 Points Solution to Homework Problem 9.4(Electric Potential Along xaxis) Problem: A region of space contains an electric field vector E = x x where = 300 N Cm . The field points in the negative x direction. Compute the potential difference, V ab (including the appropriate sign) between the point a = 1m and the point b = 2m along the xaxis....
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 Spring '08
 Stewart
 Physics, Charge, Work

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