13_Ch 15 College Physics ProblemCH15 Electric Forces and Electric Fields

13_Ch 15 College Physics ProblemCH15 Electric Forces and Electric Fields

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Electric Forces and Electric Fields 13 15.14 Assume that the third bead has charge Q and is located at 0 xd < < . Then the forces exerted on it by the +3 q charge and by the +1 q charge have magnitudes ( ) 3 2 3 e kQ q F x = and ( ) () 1 2 e kQ q F dx = respectively These forces are in opposite directions, so charge Q is in equilibrium if . This gives 3 FF = 1 ( ) 2 2 3 x −= , and solving for x , the equilibrium position is seen to be 0.634 11 3 d == + This is a position of stable equilibrium if 0 Q > . In that case, a small displacement from the equilibrium position produces a net force directed so as to move Q back toward the equilibrium position. 15.15 Consider the free-body diagram of one of the spheres given
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