Three identical conducting spheres are attached to insulating rods. Initially, s

Question

Three identical conducting spheres are attached to insulating rods. Initially, sphere A has a net charge of +2.0 C, and spheres B and C have no net charge. (a) Suppose now that sphere A is brought near sphere B, without touching. (Assume spheres A and B are far away from any other objects, including sphere C.) Is there an electrostatic force between spheres A and B? Explain why or why not. If there is a force, is it attractive or repulsive? (b) While sphere A is close to B but not touching, sphere C is touched to sphere B, then removed. Is there any net charge on spheres B or C? Explain why or why not. If there is a net charge on a sphere, is it positive or negative? Which sphere has more charge, or are they equal? Explain clearly. (c) Next, spheres B and C are grounded to remove any charge. Sphere C is moved far away. Sphere A (still having a charge of +2.0 C) is touched to sphere B (which is no longer grounded), and then taken away. How much charge is there on sphere B? How many electrons moved between spheres A and B, and in which direction?

Explanation / Answer

Given,

Qa = +2 C

a)There is an electrostatic force between A and B. Because an equal and opposite charge will be induced on sphere B. Since the charges on the spheres A and B is of opposite sign, the force between A and B will be attractive. [ Qb = -2 C ]

b) Since we learned in (a) that Qb = -2 C has been induced to B, so when C will be touched to B, and removed, it will get an oppsite amount of charge induces to C, so Qc = + 2 C. The charges on spehere are equal but opposite.

(c)Qb = -2 C ; we know charge on one electron = e = 1.6 x 10-19 C

N = -2 C / e = 2/1.6 x 10-19 = 1.25 x 1019 electrons

Hence, N = 1.25 x 1019 electrons.

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