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Unformatted text preview: CHAPTER 24 Electric Potential 1* A uniform electric field of 2 kN/C is in the x direction. A positive point charge Q = 3 C is released from rest at the origin. ( a ) What is the potential difference V (4 m) V (0)? ( b ) What is the change in the potential energy of the charge from x = 0 to x = 4 m? ( c ) What is the kinetic energy of the charge when it is at x = 4 m? ( d ) Find the potential V ( x ) if V ( x ) is chosen to be ( d ) zero at x = 0, ( e ) 4 kV at x = 0, and ( f ) zero at x = 1 m. ( a ) Use Equ. 242 b ; V = E x ( b ) U = q V ( c ) Use energy conservation ( d ), ( e ), ( f ) Use Equ. 242 b V = 8 kV U = 24 mJ K = 24 mJ ( d ) V ( x ) = (2 kV/m) x ; ( e ) V ( x ) = 4 kV (2 kV/m) x ; ( f ) V ( x ) = 2 kV (2 kV/m) x 2 An infinite plane of surface charge density = +2.5 C/m 2 is in the yz plane. ( a ) What is the magnitude of the electric field in newtons per coulomb? In volts per meter? What is the direction of E for positive values of x ? ( b ) What is the potential difference V b V a when point b is at x = 20 cm and point a is at x = 50 cm? ( c ) How much work is required by an outside agent to move a test charge q = + 1 .5 nC from point a to point b ? ( a ) E x = /2 ( b ) V = E x x ( c ) W = U = q V E x = (2.5 1 6 /2 8.85 1 1 2 ) N/C = 1 4 1 kN/C V b V a = ( 1 4 1 0.3) kV = 42.4 kV W = (42.4 1 3 1 .5 1 9 ) J = 63.6 J 3 Two large parallel conducting plates separated by 1 0 cm carry equal and opposite surface charge densities such that the electric field between them is uniform. The difference in potential between the plates is 500 V. An electron is released from rest at the negative plate. ( a ) What is the magnitude of the electric field between the plates? Is the positive or negative plate at the higher potential? ( b ) Find the work done by the electric field on the electron as the electron moves from the negative plate to the positive plate. Express your answer in both electron volts and joules. ( c ) What is the change in potential energy of the electron when it moves from the negative plate to the positive plate? What is its kinetic energy when it reaches the positive plate? ( a ) E is uniform; E = V / x (b) W = q V E = 500/0. 1 V/m = 5 kV/m; high V at the positive plate W = 500 1 .6 1 1 9 J = 8 1 1 7 J = 500 eV Chapter 24 Electric Potential (c) U = W ; K = W U = 500 eV; K = 500 eV 4 Explain the distinction between electric potential and electrostatic potential energy. The difference is analogous to that between gravitational potential and gravitational potential energy....
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This homework help was uploaded on 04/09/2008 for the course PHYS 161,260,27 taught by Professor Staff during the Spring '08 term at Maryland.
 Spring '08
 staff
 Charge, Electric Potential

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