Problem: A metal sphere is given a charge of – 3.0 x 10-6 C and a second identical sphere of
+2.0 x 10-6 C. The sphere are separated by a distance of 0.010 meter. (a) What is
the force between them? This is attractive or repulsive? (b) the sphere are brought
into contact with each other. What happen as a result of this contact? The sphere is
again separated by 0.010 m. what is now the force between them? Is this attractive
or repulsive force?
(a) We can find the force between the spheres from the Coulomb's law:
The magnitude of the electric force between the spheres is 540 N. Since the two charges are opposite in sign they will attract each other, therefore, the direction of the electric force is attractive (also, the sign minus indicates that the direction is attractive).
(b) When the spheres are brought into contact with each other, the charge will shared between the two spheres (each sphere has the same amount of charge):
(c) We can find the force between the spheres from the Coulomb's law:
The magnitude of the electric force between the spheres is 22.5 N. Since the two charges are both negatively charged they will repel each other, therefore, the direction of the electric force is repulsive (also, the sign plus indicates that the direction is repulsive).
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