1. Three similar metal spheres of the same radius and mass on insulated stands a

Question

1. Three similar metal spheres of the same radius and mass on insulated stands are initially charged as follows: sphere A has +6.0 nC charge, sphere B has –2.0 nC of charge, and sphere C is neutral. In this order, the spheres are touched for long enough for the charges to come to equilibrium and then separated again. Sphere A contacts B (and then separates.) Sphere A then touches C (and then separates.) Sphere C then touches B (and then separates.) After all this touching and separating, what is the charge on each sphere? Show that the total charge at the beginning and at the end has not changed (that is, that charge is conserved.)

Explanation / Answer

Initially :

Qa = 6 nC           , Qb = - 2nC              , Qc =0

Total charge = Qa + Qb +Qc = 6 -2 +0 = 4 nC

after touching A and B :

Qa = 6 + (-2) / 2 = 2 nC           , Qb = 2 nC           , Qc =0

after touching A and C :

Qa = 2 + (0) / 2 = 1 nC   , Qb = 2 nC           , Qc =1 nC

after touching B and C :

Qa = 1 nC , Qb = (2 + 1)/2 = 1.5 nC        , Qc = (2 + 1)/2 = 1.5 nC

Total charge = Qa + Qb +Qc = 1 +1.5 + 1.5 = 4 nC

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