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Unformatted text preview: Potential Potential Energy of Point Charges RHJansen Potential Energy
m1 r 1 2 U g =  m2 q1 r q2 12 UE = 1 2 Wg =  12 WE = The easiest zero point is infinity RHJansen Example 1
12 WE = Determine the work required to bring a 2.0 C charge at infinity to a point that is 50 cm from a 4.0 C charge. 12 12 WE =  0
WE = ( 9 109 )
6 6 ( 2.0 10 ) ( 4.0 10 ) ( 0.50 )
6 6 ( 2.0 10 ) ( 4.0 10 )  ( 9 109 ) 6 6 ( 2.0 10 ) ( 4.0 10 ) ( ) WE = ( 9 109 ) WE = 0.144 ( 0.50 ) 0 RHJansen Potential Energy of Multiple Charges UE = 12 2 3 13 UE = + + 12 23 13
q2 r q1 r r q3 12 2 3 13 UE = + + 12 23 13
Potential energy can be positive or negative. The sign on the charge matters. RHJansen Example 2 Three 4 C charges located at the vertices of an equilateral triangle with sides 20 cm separate so the distance doubles. Determine the work done in this process. q2 r r r q3 q1 2r q3 2r q2 2r q1 W = E . Subtract initial energy from final energy. WE = + +  + + 2 2 2 3 3 3 WE =  =  = 2.16 2 RHJansen Potential Energy is Related to Force
The relationship is given in the work formula. W = U = For every integral formula there is a corresponding derivative formula (and vice versa). F= W = F= Don't forget about work energy theorem. This is true for all force and energy pairs. Let's look at the long range field forces of gravity and electricity. RHJansen Potential Energy is Related to Force
W = F= WE = Wg = Fg = FE = FE = U g = Fg = U E = RHJansen ...
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This note was uploaded on 07/21/2009 for the course PHYSICS 7B taught by Professor Packard during the Spring '08 term at University of California, Berkeley.
 Spring '08
 Packard
 Physics, Charge, Energy, Potential Energy, Work

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