Question

Two tiny conducting spheres are identical and  carry charges of 3.94 micro-Coulomb and -2.39 micro-Coulomb.They are separated by a distance of  5.89 cm.The spheres are brought into contact and then separated back to the original distance. Determine the magnitude of the force that each sphere now experiences, and state whether the force is attractive or repulsive.

Answer 1

Electrostatic force is given by,

F = k*q1*q2/d^2

k = 9*10^9

if spheres are brought into contact then total charge will equally distribute on each sphere

Qa1 = Qb1 = (Qa0 + Qb0)/2

given, Qa0 = initial charge on sphere 'a' = 3.94 C

Qb0 = initial charge on sphere 'b' = -2.39 C

then, Qa1 = Qb1 = (3.94-2.39)/2 = 0.775 C

Qa1 = 0.775 C

Qb1 = 0.775 C

r = distance between spheres = 5.89 cm = 0.0589 m

Now Force will be

F = 9*10^9*(0.775*10^-6)^2/0.0589^2

F = 1.558 N (since both sphere have positive charge so force will be repulsive.)

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