Question

what should be the charge on the sphere of radius 4 cm, so that when it is brought in contact with another sphere of radius 2 cm carrying charge 10*10-6 C , there is no transfer of charge

Answer 1

Charge always flow from high potential to low potential. If both sphere's potential shame there will be no flow of charge

Sphere of radius 2cm
V = Kq/r = (9 x 10^9 x 10 x 10^-6)/0.02
V = 4.5 x 10^6 v


Sphere of radius 4cm
Q = Vr/k
Q = (4.5 x 10^6 x 0.04)/9 x 10^9
Q = 2 x 10^-5