# The potential energy would decrease if the charge

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Unformatted text preview: g the three charges in infinitely far away? A) 0 Q2 1 B) ∆U = +1 4πε 0 d Q2 1 C) ∆U = −1 4πε d 0 2 Q1 ∆ D) U = +2 4πε d 0 Q2 1 E) ∆U = −2 4πε d 0 Q BB d d d Q 1 Q2 W = ∑ Wi = + 4πε 0 d Q 1 Q2 ∆U = − 4πε 0 d Work to bring in first charge: W1 = 0 Work to bring in second charge : Work to bring in third charge : 29 1 Q2 W2 = + 4πε 0 d 1 Q2 1 Q2 W3 = + − =0 4πε 0 d 4πε 0 d Preflight 4 Preflight 4 40 30 20 10 0 A B C D Adding a charge will add both a positive term and a negative term to the potential energy equation. Those terms will cancel each other out and there will be no change equation. The potential energy would decrease if the charge were positive, yet increase if negative. 31 BB BB Preflight 6 Preflight 6 BB Which is right, C or D ? 40 Since the charges are opposite signs, there will be some radius1 and radius2 that the third charge can be placed at where the change in potential energy of the system is 0. 30 20 Bringing in another charge would either increase of decrease the total potential energy of the system. 10 0 34 C D Example BB A positive charge q is placed at x=0 and a negative charge ­2q is placed at x=d. At how many different places along the x axis could another positive charge be placed without changing the total potential energy of the system? q X=0 A) B) C) D) 37 0 1 2 3 -2q...
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## This document was uploaded on 02/13/2014.

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