What should be the charge on a sphere of radius 2 cm so that when it is brought in contact with another sphere of radius 5 cm carrying a charge of 10μC, there is no transfer of charge between the spheres?
Their potential must be same for the charge transfer to occur .So
K×q1r1=K×q2r2
q1=(q2r2)×r1
q1=10×10−65×2
q1=4μC